EVALUATING THE SENSITIVITY OF A SUBSURFACE MULTICOMPONENT REACTIVE TRANSPORT MODEL WITH RESPECT TO TRANSPORT AND REACTION PARAMETERS

EPA Science Inventory

The input variables for a numerical model of reactive solute transport in groundwater include both transport parameters, such as hydraulic conductivity and infiltration, and reaction parameters that describe the important chemical and biological processes in the system. These pa...

TOUGHREACT: a new code of the TOUGH Family for Non-Isothermal multiphase reactive geochemical transport in variably saturated geologic media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Tianfu; Sonnenthal, Eric; Spycher, Nicolas

Coupled modeling of subsurface multiphase fluid and heat flow, solute transport and chemical reactions can be used for the assessment of acid mine drainage remediation, waste disposal sites, hydrothermal convection, contaminant transport, and groundwater quality. We have developed a comprehensive numerical simulator, TOUGHREACT, which considers non-isothermal multi-component chemical transport in both liquid and gas phases. A wide range of subsurface thermo-physical-chemical processes is considered under various thermohydrological and geochemical conditions of pressure, temperature, water saturation, and ionic strength. The code can be applied to one-, two- or three-dimensional porous and fractured media with physical and chemical heterogeneity.

Uranium transport in a crushed granodiorite: Experiments and reactive transport modeling

DOE PAGES

Dittrich, T. M.; Reimus, P. W.

2015-02-12

The primary objective of this study was to develop and demonstrate an experimental method to refine and better parameterize process models for reactive contaminant transport in aqueous subsurface environments and to reduce conservatism in such models without attempting to fully describe the geochemical system.

Debates—Stochastic subsurface hydrology from theory to practice: The relevance of stochastic subsurface hydrology to practical problems of contaminant transport and remediation. What is characterization and stochastic theory good for?

NASA Astrophysics Data System (ADS)

Fiori, A.; Cvetkovic, V.; Dagan, G.; Attinger, S.; Bellin, A.; Dietrich, P.; Zech, A.; Teutsch, G.

2016-12-01

The emergence of stochastic subsurface hydrology stemmed from the realization that the random spatial variability of aquifer properties has a profound impact on solute transport. The last four decades witnessed a tremendous expansion of the discipline, many fundamental processes and principal mechanisms being identified. However, the research findings have not impacted significantly the application in practice, for several reasons which are discussed. The paper discusses the current status of stochastic subsurface hydrology, the relevance of the scientific results for applications and it also provides a perspective to a few possible future directions. In particular, we discuss how the transfer of knowledge can be facilitated by identifying clear goals for characterization and modeling application, relying on recent recent advances in research in these areas.

BLT-EC (Breach, Leach and Transport-Equilibrium Chemistry) data input guide. A computer model for simulating release and coupled geochemical transport of contaminants from a subsurface disposal facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacKinnon, R.J.; Sullivan, T.M.; Kinsey, R.R.

1997-05-01

The BLT-EC computer code has been developed, implemented, and tested. BLT-EC is a two-dimensional finite element computer code capable of simulating the time-dependent release and reactive transport of aqueous phase species in a subsurface soil system. BLT-EC contains models to simulate the processes (container degradation, waste-form performance, transport, chemical reactions, and radioactive production and decay) most relevant to estimating the release and transport of contaminants from a subsurface disposal system. Water flow is provided through tabular input or auxiliary files. Container degradation considers localized failure due to pitting corrosion and general failure due to uniform surface degradation processes. Waste-form performancemore » considers release to be limited by one of four mechanisms: rinse with partitioning, diffusion, uniform surface degradation, and solubility. Transport considers the processes of advection, dispersion, diffusion, chemical reaction, radioactive production and decay, and sources (waste form releases). Chemical reactions accounted for include complexation, sorption, dissolution-precipitation, oxidation-reduction, and ion exchange. Radioactive production and decay in the waste form is simulated. To improve the usefulness of BLT-EC, a pre-processor, ECIN, which assists in the creation of chemistry input files, and a post-processor, BLTPLOT, which provides a visual display of the data have been developed. BLT-EC also includes an extensive database of thermodynamic data that is also accessible to ECIN. This document reviews the models implemented in BLT-EC and serves as a guide to creating input files and applying BLT-EC.« less

The Subsurface Flow and Transport Laboratory: A New Department of Energy User's Facility for Intermediate-Scale Experimentation

NASA Astrophysics Data System (ADS)

Wietsma, T. W.; Oostrom, M.; Foster, N. S.

2003-12-01

Intermediate-scale experiments (ISEs) for flow and transport are a valuable tool for simulating subsurface features and conditions encountered in the field at government and private sites. ISEs offer the ability to study, under controlled laboratory conditions, complicated processes characteristic of mixed wastes and heterogeneous subsurface environments, in multiple dimensions and at different scales. ISEs may, therefore, result in major cost savings if employed prior to field studies. A distinct advantage of ISEs is that researchers can design physical and/or chemical heterogeneities in the porous media matrix that better approximate natural field conditions and therefore address research questions that contain the additional complexity of processes often encountered in the natural environment. A new Subsurface Flow and Transport Laboratory (SFTL) has been developed for ISE users in the Environmental Spectroscopy & Biogeochemistry Facility in the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory (PNNL). The SFTL offers a variety of columns and flow cells, a new state-of-the-art dual-energy gamma system, a fully automated saturation-pressure apparatus, and analytical equipment for sample processing. The new facility, including qualified staff, is available for scientists interested in collaboration on conducting high-quality flow and transport experiments, including contaminant remediation. Close linkages exist between the SFTL and numerical modelers to aid in experimental design and interpretation. This presentation will discuss the facility and outline the procedures required to submit a proposal to use this unique facility for research purposes. The W. R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility, is sponsored by the U.S. Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

Understanding Subsurface Colloid Behavior: A New Visualization Technique and the Application of Geo-Centrifuge Modeling

NASA Astrophysics Data System (ADS)

Yoon, J. S.; Culligan, P. J.; Germaine, J. T.

2003-12-01

Subsurface colloid behavior has recently drawn attention because colloids are suspected of enhancing contaminant transport in groundwater systems. To better understand the processes by which colloids move through the subsurface, and in particular the vadose zone, a new technique that enables real-time visualization of colloid particles as they move through a porous medium has been developed. This visualization technique involves the use of laser induced fluorescent particles and digital image processing to directly observe particles moving through a porous medium consisting of soda-lime glass beads and water in a transparent experimental box of 10.0cm\\x9D27.9cm\\x9D2.38cm. Colloid particles are simulated using commercially available micron sized particles that fluoresce under argon-ion laser light. The fluorescent light given off from the particles is captured through a camera filter, which lets through only the emitted wavelength of the colloid particles. The intensity of the emitted light is proportional to the colloid particle concentration. The images of colloid movement are captured by a MagnaFire digital camera; a cooled CCD digital camera produced by Optronics. This camera enables real-time capture of images to a computer, thereby allowing the images to be processed immediately. The images taken by the camera are analyzed by the ImagePro software from Media Cybernetics, which contains a range of counting, sizing, measuring, and image enhancement tools for image processing. Laboratory experiments using the new technique have demonstrated the existence of both irreversible and reversible sites for colloid entrapment during uniform saturated flow in a homogeneous porous medium. These tests have also shown a dependence of colloid entrapment on velocity. Models for colloid transport currently available in the literature have proven to be inadequate predictors for the experimental observations, despite the simplicity of the system studied. To further extend the work, the visualization technique has been developed for use on the geo-centrifuge. The advantage that the geo-centrifuge has for investigating subsurface colloid behavior, is the ability to simulate unsaturated transport mechanisms under well simulated field moisture profiles and in shortened periods of time. A series of tests to investigate colloid transport during uniform saturated flow is being used to examine basic scaling laws for colloid transport under enhanced gravity. The paper will describe the new visualization technique, its use in geo-centrifuge testing and observations on scaling relationships for colloid transport during geo-centrifuge experiments. Although the visualization technique has been developed for investigating subsurface colloid behavior, it does have application in other areas of investigation, including the investigation of microbial behavior in the subsurface.

FATE AND TRANSPORT OF MTBE AND OTHER GASOLINE COMPONENTS

EPA Science Inventory

This book chapter reviews the processes and interactions that control the transport and fate of MTBE and TBA in the subsurface. It describes the transport and fate of vapors of MTBE in the unsaturated zone, the partitioning of MTBE from gasoline spills directly into water, and t...

MODELING MICROBIAL TRANSPORT IN SOIL AND GROUNDWATER: MICROBIOLOGISTS CAN ASSIST IN THE DEVELOPMENT OF MODELS OF CONTAMINANT TRANSPORT

EPA Science Inventory

A large body of literature describes the processes affecting the fate of microorganisms in the subsurface environment (i.e., soil and groundwater). The fate of microorganisms depends on two main components: survival and transport. other components must be considered when determin...

TRANSPORT AND SURVIVAL OF VIRUSES IN THE SUBSURFACE PROCESSES, EXPERIMENTS, AND SIMULATION MODELS

EPA Science Inventory

The remediation of ground water contaminated with waterborne pathogens, in particular with viruses, is based on their probable or actual ability to be transported from the source of origin to a point of withdrawal while maintaining the capacity to cause infections. The transport ...

Hydrology of the Bonneville Salt Flats, northwestern Utah, and simulation of ground-water flow and solute transport in the shallow-brine aquifer

USGS Publications Warehouse

Mason, James L.; Kipp, Kenneth L.

1998-01-01

This report describes the hydrologic system of the Bonneville Salt Flats with emphasis on the mechanisms of solute transport. Variable-density, three-dimensional computer simulations of the near-surface part of the ground-water system were done to quantify both the transport of salt dissolved in subsurface brine that leaves the salt-crust area and the salt dissolved and precipitated on the land surface. The study was designed to define the hydrology of the brine ground-water system and the natural and anthropogenic processes causing salt loss, and where feasible, to quantify these processes. Specific areas of study include the transport of salt in solution by ground-water flow and the transport of salt in solution by wind-driven ponds and the subsequent salt precipitation on the surface of the playa upon evaporation or seepage into the subsurface. In addition, hydraulic and chemical changes in the hydrologic system since previous studies were documented.

Discrete Fracture Network Modeling and Simulation of Subsurface Transport for the Topopah Springs and Lava Flow Aquifers at Pahute Mesa, FY 15 Progress Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makedonska, Nataliia; Kwicklis, Edward Michael; Birdsell, Kay Hanson

This progress report for fiscal year 2015 (FY15) describes the development of discrete fracture network (DFN) models for Pahute Mesa. DFN models will be used to upscale parameters for simulations of subsurface flow and transport in fractured media in Pahute Mesa. The research focuses on modeling of groundwater flow and contaminant transport using DFNs generated according to fracture characteristics observed in the Topopah Spring Aquifer (TSA) and the Lava Flow Aquifer (LFA). This work will improve the representation of radionuclide transport processes in large-scale, regulatory-focused models with a view to reduce pessimistic bounding approximations and provide more realistic contaminant boundarymore » calculations that can be used to describe the future extent of contaminated groundwater. Our goal is to refine a modeling approach that can translate parameters to larger-scale models that account for local-scale flow and transport processes, which tend to attenuate migration.« less

Implementation of gINT software at the Virginia Department of Transportation.

DOT National Transportation Integrated Search

2008-01-01

A set of software tools was developed to enable staff of the Virginia Department of Transportation (VDOT) and consultants to streamline processing of subsurface exploration data. Built around the gINT program (geotechnical database and graphics packa...

Seasonal Variability in Vadose zone biodegradation at a crude oil pipeline rupture site

USGS Publications Warehouse

Sihota, Natasha J.; Trost, Jared J.; Bekins, Barbara; Berg, Andrew M.; Delin, Geoffrey N.; Mason, Brent E.; Warren, Ean; Mayer, K. Ulrich

2016-01-01

Understanding seasonal changes in natural attenuation processes is critical for evaluating source-zone longevity and informing management decisions. The seasonal variations of natural attenuation were investigated through measurements of surficial CO2 effluxes, shallow soil CO2 radiocarbon contents, subsurface gas concentrations, soil temperature, and volumetric water contents during a 2-yr period. Surficial CO2 effluxes varied seasonally, with peak values of total soil respiration (TSR) occurring in the late spring and summer. Efflux and radiocarbon data indicated that the fractional contributions of natural soil respiration (NSR) and contaminant soil respiration (CSR) to TSR varied seasonally. The NSR dominated in the spring and summer, and CSR dominated in the fall and winter. Subsurface gas concentrations also varied seasonally, with peak values of CO2 and CH4 occurring in the fall and winter. Vadose zone temperatures and subsurface CO2 concentrations revealed a correlation between contaminant respiration and temperature. A time lag of 5 to 7 mo between peak subsurface CO2 concentrations and peak surface efflux is consistent with travel-time estimates for subsurface gas migration. Periods of frozen soils coincided with depressed surface CO2 effluxes and elevated CO2 concentrations, pointing to the temporary presence of an ice layer that inhibited gas transport. Quantitative reactive transport simulations demonstrated aspects of the conceptual model developed from field measurements. Overall, results indicated that source-zone natural attenuation (SZNA) rates and gas transport processes varied seasonally and that the average annual SZNA rate estimated from periodic surface efflux measurements is 60% lower than rates determined from measurements during the summer.

Dynamics of nonreactive solute transport in the permafrost environment

NASA Astrophysics Data System (ADS)

Svyatskiy, D.; Coon, E. T.; Moulton, J. D.

2017-12-01

As part of the DOE Office of Science Next Generation Ecosystem Experiment, NGEE-Arctic, researchers are developing process-rich models to understand and predict the evolution of water sources and hydrologic flow pathways resulting from degrading permafrost. The sources and interaction of surface and subsurface water and flow paths are complex in space and time due to strong interplay between heterogeneous subsurface parameters, the seasonal to decadal evolution of the flow domain, climate driven melting and release of permafrost ice as a liquid water source, evolving surface topography and highly variable meteorological data. In this study, we seek to characterize the magnitude of vertical and lateral subsurface flows in a cold, wet tundra, polygonal landscape characteristic of the Barrow Peninsula, AK. To better understand the factors controlling water flux partitioning in these low gradient landscapes, NGEE researchers developed and are applying the Advanced Terrestrial Simulator (ATS), which fully couples surface and subsurface flow and energy processes, snow distribution and atmospheric forcing. Here we demonstrate the integration of a new solute transport model within the ATS, which enables the interpretation of applied and natural tracer experiments and observations aimed at quantifying water sources and flux partitioning. We examine the role of ice wedge polygon structure, freeze-thaw processes and soil properties on the seasonal transport of water within and through polygons features, and compare results to tracer experiments on 2D low-centered and high-centered transects corresponding to artificial as well as realistic topographical data from sites in polygonal tundra. These simulations demonstrate significant difference between flow patterns between permafrost and non-permafrost environments due to active layer freeze-thaw processes.

NIGHTHAWK - A Program for Modeling Saturated Batch and Column Experiments Incorporating Equilibrium and Kinetic Biogeochemistry

EPA Science Inventory

NIGHTHAWK simulates the fate and transport of biogeochemically reactive contaminants in the saturated subsurface. Version 1.2 supports batch and one- dimensional advective-dispersive-reactive transport involving a number of biogeochemical processes, including: microbially-mediate...

ITE CHARACTERIZATION TO SUPPORT CONCEPTUAL MODEL DEVELOPMENT FOR SUBSURFACE RADIONUCLIDE TRANSPORT

EPA Science Inventory

Remediation of radionuclide contaminants in ground water often begins with the development of conceptual and analytical models that guide our understanding of the processes controlling radionuclide transport. The reliability of these models is often predicated on the collection o...

Review on subsurface colloids and colloid-associated contaminant transport in saturated porous media.

PubMed

Kanti Sen, Tushar; Khilar, Kartic C

2006-02-28

In this review article, the authors present up-to-date developments on experimental, modeling and field studies on the role of subsurface colloidal fines on contaminant transport in saturated porous media. It is a complex phenomenon in porous media involving several basic processes such as colloidal fines release, dispersion stabilization, migration and fines entrapment/plugging at the pore constrictions and adsorption at solid/liquid interface. The effects of these basic processes on the contaminant transport have been compiled. Here the authors first present the compilation on in situ colloidal fines sources, release, stabilization of colloidal dispersion and migration which are a function of physical and chemical conditions of subsurface environment and finally their role in inorganic and organic contaminants transport in porous media. The important aspects of this article are as follows: (i) it gives not only complete compilation on colloidal fines-facilitated contaminant transport but also reviews the new role of colloidal fines in contaminant retardation due to plugging of pore constrictions. This plugging phenomenon also depends on various factors such as concentration of colloidal fines, superficial velocity and bead-to-particle size ratio. This plugging-based contaminant transport can be used to develop containment technique in soil and groundwater remediation. (ii) It also presents the importance of critical salt concentration (CSC), critical ionic strength for mixed salt, critical shear stressor critical particle concentration (CPC) on in situ colloidal fines release and migration and consequently their role on contaminant transport in porous media. (iii) It also reviews another class of colloidal fines called biocolloids and their transport in porous media. Finally, the authors highlight the future research based on their critical review on colloid-associated contaminant transport in saturated porous media.

Transport of Chemical Vapors from Subsurface Sources to Atmosphere as Affected by Shallow Subsurface and Atmospheric Conditions

NASA Astrophysics Data System (ADS)

Rice, A. K.; Smits, K. M.; Hosken, K.; Schulte, P.; Illangasekare, T. H.

2012-12-01

Understanding the movement and modeling of chemical vapor through unsaturated soil in the shallow subsurface when subjected to natural atmospheric thermal and mass flux boundary conditions at the land surface is of importance to applications such as landmine detection and vapor intrusion into subsurface structures. New, advanced technologies exist to sense chemical signatures at the land/atmosphere interface, but interpretation of these sensor signals to make assessment of source conditions remains a challenge. Chemical signatures are subject to numerous interactions while migrating through the unsaturated soil environment, attenuating signal strength and masking contaminant source conditions. The dominant process governing movement of gases through porous media is often assumed to be Fickian diffusion through the air phase with minimal or no quantification of other processes contributing to vapor migration, such as thermal diffusion, convective gas flow due to the displacement of air, expansion/contraction of air due to temperature changes, temporal and spatial variations of soil moisture and fluctuations in atmospheric pressure. Soil water evaporation and interfacial mass transfer add to the complexity of the system. The goal of this work is to perform controlled experiments under transient conditions of soil moisture, temperature and wind at the land/atmosphere interface and use the resulting dataset to test existing theories on subsurface gas flow and iterate between numerical modeling efforts and experimental data. Ultimately, we aim to update conceptual models of shallow subsurface vapor transport to include conditionally significant transport processes and inform placement of mobile sensors and/or networks. We have developed a two-dimensional tank apparatus equipped with a network of sensors and a flow-through head space for simulation of the atmospheric interface. A detailed matrix of realistic atmospheric boundary conditions was applied in a series of experiments. Water saturation, capillary pressure, air and soil temperature, and relative humidity were continuously monitored. Aqueous TCE was injected into the tank below the water table and allowed to volatilize. TCE concentration exiting the tank head space was measured through interval sampling by direct injection into a gas chromatograph. To quantify the transient concentration of TCE vapor in the soil pore space a novel use of Solid Phase Micro-Extraction (SPME) was developed. Results from our numerical simulations were compared with the experimental data, which demonstrated the importance of considering the interaction of the atmosphere with the subsurface in conceptualization and numerical model development. Results also emphasize that soil saturation and transient sorption have a significant effect on vapor transport through the vadose zone. Follow-up tests and detailed analyses are still underway. Additional applications of this work include carbon sequestration leakage, methane contamination in the shallow subsurface and environmental impact of hydraulic fracturing.

TRANSPORT AND FATE OF CONTAMINANTS IN THE SUBSURFACE

EPA Science Inventory

This publication is based on a series of t.technology Transfer seminars that were conducted in 1987 and 1988. The document provides an overview of many of the issues associated with the physical, chemical and biological processes that control contaminant transport in the subsurfa...

Holocene evolution of the North Atlantic subsurface transport

NASA Astrophysics Data System (ADS)

Repschläger, Janne; Garbe-Schönberg, Dieter; Weinelt, Mara; Schneider, Ralph

2017-04-01

Previous studies suggested that short-term freshening events in the subpolar gyre can be counterbalanced by advection of saline waters from the subtropical gyre and thus stabilize the Atlantic Meridional Overturning Circulation (AMOC). However, little is known about the inter-gyre transport pathways. Here, we infer changes in surface and subsurface transport between the subtropical and polar North Atlantic during the last 11 000 years, by combining new temperature and salinity reconstructions obtained from combined δ18O and Mg / Ca measurements on surface and subsurface dwelling foraminifera with published foraminiferal abundance data from the subtropical North Atlantic, and with salinity and temperature data from the tropical and subpolar North Atlantic. This compilation implies an overall stable subtropical warm surface water transport since 10 ka BP. In contrast, subsurface warm water transport started at about 8 ka but still with subsurface heat storage in the subtropical gyre. The full strength of intergyre exchange was probably reached only after the onset of northward transport of warm saline subsurface waters at about 7 ka BP, associated with the onset of the modern AMOC mode. A critical evaluation of different potential forcing mechanisms leads to the assumption that freshwater supply from the Laurentide Ice Sheet was the main control on subtropical to subpolar ocean transport at surface and subsurface levels.

Simulating pathways of subsurface oil in the Faroe-Shetland Channel using an ocean general circulation model.

PubMed

Main, C E; Yool, A; Holliday, N P; Popova, E E; Jones, D O B; Ruhl, H A

2017-01-15

Little is known about the fate of subsurface hydrocarbon plumes from deep-sea oil well blowouts and their effects on processes and communities. As deepwater drilling expands in the Faroe-Shetland Channel (FSC), oil well blowouts are a possibility, and the unusual ocean circulation of this region presents challenges to understanding possible subsurface oil pathways in the event of a spill. Here, an ocean general circulation model was used with a particle tracking algorithm to assess temporal variability of the oil-plume distribution from a deep-sea oil well blowout in the FSC. The drift of particles was first tracked for one year following release. Then, ambient model temperatures were used to simulate temperature-mediated biodegradation, truncating the trajectories of particles accordingly. Release depth of the modeled subsurface plumes affected both their direction of transport and distance travelled from their release location, and there was considerable interannual variability in transport. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Capabilities of seismic and georadar 2D/3D imaging of shallow subsurface of transport route using the Seismobile system

NASA Astrophysics Data System (ADS)

Pilecki, Zenon; Isakow, Zbigniew; Czarny, Rafał; Pilecka, Elżbieta; Harba, Paulina; Barnaś, Maciej

2017-08-01

In this work, the capabilities of the Seismobile system for shallow subsurface imaging of transport routes, such as roads, railways, and airport runways, in different geological conditions were presented. The Seismobile system combines the advantages of seismic profiling using landstreamer and georadar (GPR) profiling. It consists of up to four seismic measuring lines and carriage with a suspended GPR antenna. Shallow subsurface recognition may be achieved to a maximum width of 10.5 m for a distance of 3.5 m between the measurement lines. GPR measurement is performed in the axis of the construction. Seismobile allows the measurement time, labour and costs to be reduced due to easy technique of its installation, remote data transmission from geophones to accompanying measuring modules, automated location of the system based on GPS and a highly automated method of seismic wave excitation. In this paper, the results of field tests carried out in different geological conditions were presented. The methodologies of acquisition, processing and interpretation of seismic and GPR measurements were broadly described. Seismograms and its spectrum registered by Seismobile system were compared to the ones registered by Geode seismograph of Geometrix. Seismic data processing and interpretation software allows for the obtaining of 2D/3D models of P- and S-wave velocities. Combined seismic and GPR results achieved sufficient imaging of shallow subsurface to a depth of over a dozen metres. The obtained geophysical information correlated with geological information from the boreholes with good quality. The results of performed tests proved the efficiency of the Seismobile system in seismic and GPR imaging of a shallow subsurface of transport routes under compound conditions.

Subsurface conditions in hydrothermal vents inferred from diffuse flow composition, and models of reaction and transport

NASA Astrophysics Data System (ADS)

Larson, B. I.; Houghton, J. L.; Lowell, R. P.; Farough, A.; Meile, C. D.

2015-08-01

Chemical gradients in the subsurface of mid-ocean ridge hydrothermal systems create an environment where minerals precipitate and dissolve and where chemosynthetic organisms thrive. However, owing to the lack of easy access to the subsurface, robust knowledge of the nature and extent of chemical transformations remains elusive. Here, we combine measurements of vent fluid chemistry with geochemical and transport modeling to give new insights into the under-sampled subsurface. Temperature-composition relationships from a geochemical mixing model are superimposed on the subsurface temperature distribution determined using a heat flow model to estimate the spatial distribution of fluid composition. We then estimate the distribution of Gibb's free energies of reaction beneath mid oceanic ridges and by combining flow simulations with speciation calculations estimate anhydrite deposition rates. Applied to vent endmembers observed at the fast spreading ridge at the East Pacific Rise, our results suggest that sealing times due to anhydrite formation are longer than the typical time between tectonic and magmatic events. The chemical composition of the neighboring low temperature flow indicates relatively uniform energetically favorable conditions for commonly inferred microbial processes such as methanogenesis, sulfate reduction and numerous oxidation reactions, suggesting that factors other than energy availability may control subsurface microbial biomass distribution. Thus, these model simulations complement fluid-sample datasets from surface venting and help infer the chemical distribution and transformations in subsurface flow.

Soil Carbon Dioxide Production and Surface Fluxes: Subsurface Physical Controls

NASA Astrophysics Data System (ADS)

Risk, D.; Kellman, L.; Beltrami, H.

Soil respiration is a critical determinant of landscape carbon balance. Variations in soil temperature and moisture patterns are important physical processes controlling soil respiration which need to be better understood. Relationships between soil respi- ration and physical controls are typically addressed using only surface flux data but other methods also exist which permit more rigorous interpretation of soil respira- tion processes. Here we use a combination of subsurface CO_{2} concentrations, surface CO_{2} fluxes and detailed physical monitoring of the subsurface envi- ronment to examine physical controls on soil CO_{2} production at four climate observatories in Eastern Canada. Results indicate that subsurface CO_{2} produc- tion is more strongly correlated to the subsurface thermal environment than the surface CO_{2} flux. Soil moisture was also found to have an important influence on sub- surface CO_{2} production, particularly in relation to the soil moisture - soil profile diffusivity relationship. Non-diffusive profile CO_{2} transport appears to be im- portant at these sites, resulting in a de-coupling of summertime surface fluxes from subsurface processes and violating assumptions that surface CO_{2} emissions are the result solely of diffusion. These results have implications for the study of soil respiration across a broad range of terrestrial environments.

Impacts of preferential flow on coastal groundwater-surface water interactions: The heterogeneous volcanic aquifer of Hawaii

NASA Astrophysics Data System (ADS)

Geng, X.; Kreyns, P.; Koneshloo, M.; Michael, H. A.

2017-12-01

Groundwater flow and salt transport processes are important for protection of coastal water resources and ecosystems. Geological heterogeneity has been recognized as a key factor affecting rates and patterns of groundwater flow and the evolution of subsurface salinity distributions in coastal aquifers. The hydrogeologic system of the volcanic Hawaiian Islands is characterized by lava flows that can form continuous, connected geologic structures in subsurface. Understanding the role of geological heterogeneity in aquifer salinization and water exchange between aquifers and the ocean is essential for effective assessment and management of water resources in the Hawaii islands. In this study, surface-based geostatistical techniques were adopted to generate geologically-realistic, statistically equivalent model realizations of the hydrogeologic system on the Big Island of Hawaii. The density-dependent groundwater flow and solute transport code SEAWAT was used to perform 3D simulations to investigate subsurface flow and salt transport through these random realizations. Flux across the aquifer-ocean interface, aquifer salinization, and groundwater flow pathways and associated transit times were quantified. Numerical simulations of groundwater pumping at various positions in the aquifers were also conducted, and associated impacts on saltwater intrusion rates were evaluated. Results indicate the impacts of continuous geologic features on large-scale groundwater processes in coastal aquifers.

IMPACT OF REDOX DISEQUILIBRIA ON CONTAMINANT TRANSPORT AND REMEDIATION IN SUBSURFACE SYSTEMS

EPA Science Inventory

Partitioning to mineral surfaces exerts significant control on inorganic contaminant transport in subsurface systems. Remedial technologies for in-situ treatment of subsurface contamination are frequently designed to optimize the efficiency of contaminant partitioning to solid s...

Application of model abstraction techniques to simulate transport in soils

USDA-ARS?s Scientific Manuscript database

Successful understanding and modeling of contaminant transport in soils is the precondition of risk-informed predictions of the subsurface contaminant transport. Exceedingly complex models of subsurface contaminant transport are often inefficient. Model abstraction is the methodology for reducing th...

Simulating oil droplet dispersal from the Deepwater Horizon spill with a Lagrangian approach

USGS Publications Warehouse

North, Elizabeth W.; Schlag, Zachary; Adams, E. Eric; Sherwood, Christopher R.; He, Ruoying; Hyun, Hoon; Socolofsky, Scott A.

2011-01-01

An analytical multiphase plume model, combined with time-varying flow and hydrographic fields generated by the 3-D South Atlantic Bight and Gulf of Mexico model (SABGOM) hydrodynamic model, were used as input to a Lagrangian transport model (LTRANS), to simulate transport of oil droplets dispersed at depth from the recent Deepwater Horizon MC 252 oil spill. The plume model predicts a stratification-dominated near field, in which small oil droplets detrain from the central plume containing faster rising large oil droplets and gas bubbles and become trapped by density stratification. Simulated intrusion (trap) heights of ∼ 310–370 m agree well with the midrange of conductivity-temperature-depth observations, though the simulated variation in trap height was lower than observed, presumably in part due to unresolved variability in source composition (percentage oil versus gas) and location (multiple leaks during first half of spill). Simulated droplet trajectories by the SABGOM-LTRANS modeling system showed that droplets with diameters between 10 and 50 μm formed a distinct subsurface plume, which was transported horizontally and remained in the subsurface for >1 month. In contrast, droplets with diameters ≥90 μm rose rapidly to the surface. Simulated trajectories of droplets ≤50 μm in diameter were found to be consistent with field observations of a southwest-tending subsurface plume in late June 2010 reported by Camilli et al. [2010]. Model results suggest that the subsurface plume looped around to the east, with potential subsurface oil transport to the northeast and southeast. Ongoing work is focusing on adding degradation processes to the model to constrain droplet dispersal.

The Role of Subsurface Properties on Transport of Water and Trace Gases: 1D Simulations at Selected Mars Landing Sites.

NASA Astrophysics Data System (ADS)

Karatekin, O.; Gloesener, E.; Dehant, V. M. A.

2017-12-01

In this work, water ice stability and water vapour transport through porous martian subsurface are studied using a 1D diffusive model. The role of adsorption on water transfer in martian conditions is investigated as well as the range of parameters that have the largest effect on gas transport. In addition, adsorption kinetics is considered to examine its influence on the water vapor exchange between the subsurface and the atmosphere. As methane has been detected in the martian atmosphere, the subsurface model is then used to study methane diffusion in the CH4/CO2/H2O system from variable depths under the surface. The results of subsurface gas transport at selected locations/landing sites are shown and implications for present/future observations are discussed.

Conceptual Model of Iodine Behavior in the Subsurface at the Hanford Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Truex, Michael J.; Lee, Brady D.; Johnson, Christian D.

The fate and transport of 129I in the environment and potential remediation technologies are currently being studied as part of environmental remediation activities at the Hanford Site. A conceptual model describing the nature and extent of subsurface contamination, factors that control plume behavior, and factors relevant to potential remediation processes is needed to support environmental remedy decisions. Because 129I is an uncommon contaminant, relevant remediation experience and scientific literature are limited. Thus, the conceptual model also needs to both describe known contaminant and biogeochemical process information and to identify aspects about which additional information needed to effectively support remedy decisions.more » this document summarizes the conceptual model of iodine behavior relevant to iodine in the subsurface environment at the Hanford site.« less

THE ONSITE ON-LINE CALCULATORS AND TRAINING FOR SUBSURFACE CONTAMINANT TRANSPORT SITE ASSESSMENT

EPA Science Inventory

EPA has developed a suite of on-line calculators called "OnSite" for assessing transport of environmental contaminants in the subsurface. The purpose of these calculators is to provide methods and data for common calculations used in assessing impacts from subsurface contaminatio...

Final technical report for project titled Quantitative Characterization of Cell Aggregation/Adhesion as Predictor for Distribution and Transport of Microorganisms in Subsurface Environment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gu, April Z.; Wan, Kai-tak

This project aims to explore and develop enabling methodology and techniques for nano-scale characterization of microbe cell surface contact mechanics, interactions and adhesion quantities that allow for identification and quantification of indicative properties related to microorganism migration and transport behavior in porous media and in subsurface environments. Microbe transport has wide impact and therefore is of great interest in various environmental applications such as in situ or enhanced subsurface bioremediation,filtration processes for water and wastewater treatments and protection of drinking water supplies. Although great progress has been made towards understanding the identities and activities of these microorganisms in the subsurface,more » to date, little is known of the mechanisms that govern the mobility and transport of microorganisms in DOE’s contaminated sites, making the outcomes of in situ natural attenuation or contaminant stability enhancement unpredictable. Conventionally, movement of microorganisms was believed to follows the rules governing solute (particle) transport. However, recent studies revealed that cell surface properties, especially those pertaining to cell attachment/adhesion and aggregation behavior, can cause the microbe behavior to deviate from non-viable particles and hence greatly influence the mobility and distribution of microorganisms in porous media.This complexity highlights the need to obtain detailed information of cell-cell and cell-surface interactions in order to improve and refine the conceptual and quantitative model development for fate and transport of microorganisms and contaminant in subsurface. Traditional cell surface characterization methods are not sufficient to fully predict the deposition rates and transport behaviors of microorganism observed. A breakthrough of methodology that would allow for quantitative and molecular-level description of intrinsic cell surface properties indicative for cell-surface interactions is essential for the field. To tackle this, we have developed a number of new Bio-nanomechanical techniques, including reflection interference contrast microscopy (RICM) and bio-AFM (Atomic Force Microscopy), for cell adhesion-detachment measurement of the long-range surface interactions, in combination with mathematical modeling, which would allow us to characterize the mechanical behavior from single cell to multi-cell aggregate, critical thresholds for large scale coaggregation and transportation of cells and aggregates in the presence of long range inter-surface forces etc. Although some technical and mathematical challenges remain, the preliminary results promise great breakthrough potential. In this study, we investigated the cellular surface characteristics of representative bio-remediating microorganisms relevant to DOE IFRC (Integrated Field-Scale Subsurface Research Challenges) sites and their transport behaviors in porous media, aiming to draw a groundbreaking correlation between the micro-scale genetic and biological origin-based cell surface properties, the consequent mechanical adhesion and aggregation behaviors, and the macro-scale microbial mobility and retention in porous media, which are unavailable in the literature. The long-term goal is to significantly improve the mechanistic and quantitative understanding of microbial mobility, sorption, and transport within reactive transport models as needed to manipulate subsurface contaminant fate and transport predictions.« less

Two-Relaxation-Time Lattice Boltzmann Method and its Application to Advective-Diffusive-Reactive Transport

DOE PAGES

Yan, Zhifeng; Yang, Xiaofan; Li, Siliang; ...

2017-09-05

The lattice Boltzmann method (LBM) based on single-relaxation-time (SRT) or multiple-relaxation-time (MRT) collision operators is widely used in simulating flow and transport phenomena. The LBM based on two-relaxation-time (TRT) collision operators possesses strengths from the SRT and MRT LBMs, such as its simple implementation and good numerical stability, although tedious mathematical derivations and presentations of the TRT LBM hinder its application to a broad range of flow and transport phenomena. This paper describes the TRT LBM clearly and provides a pseudocode for easy implementation. Various transport phenomena were simulated using the TRT LBM to illustrate its applications in subsurface environments.more » These phenomena include advection-diffusion in uniform flow, Taylor dispersion in a pipe, solute transport in a packed column, reactive transport in uniform flow, and bacterial chemotaxis in porous media. Finally, the TRT LBM demonstrated good numerical performance in terms of accuracy and stability in predicting these transport phenomena. Therefore, the TRT LBM is a powerful tool to simulate various geophysical and biogeochemical processes in subsurface environments.« less

Two-relaxation-time lattice Boltzmann method and its application to advective-diffusive-reactive transport

NASA Astrophysics Data System (ADS)

Yan, Zhifeng; Yang, Xiaofan; Li, Siliang; Hilpert, Markus

2017-11-01

The lattice Boltzmann method (LBM) based on single-relaxation-time (SRT) or multiple-relaxation-time (MRT) collision operators is widely used in simulating flow and transport phenomena. The LBM based on two-relaxation-time (TRT) collision operators possesses strengths from the SRT and MRT LBMs, such as its simple implementation and good numerical stability, although tedious mathematical derivations and presentations of the TRT LBM hinder its application to a broad range of flow and transport phenomena. This paper describes the TRT LBM clearly and provides a pseudocode for easy implementation. Various transport phenomena were simulated using the TRT LBM to illustrate its applications in subsurface environments. These phenomena include advection-diffusion in uniform flow, Taylor dispersion in a pipe, solute transport in a packed column, reactive transport in uniform flow, and bacterial chemotaxis in porous media. The TRT LBM demonstrated good numerical performance in terms of accuracy and stability in predicting these transport phenomena. Therefore, the TRT LBM is a powerful tool to simulate various geophysical and biogeochemical processes in subsurface environments.

Two-Relaxation-Time Lattice Boltzmann Method and its Application to Advective-Diffusive-Reactive Transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Zhifeng; Yang, Xiaofan; Li, Siliang

The lattice Boltzmann method (LBM) based on single-relaxation-time (SRT) or multiple-relaxation-time (MRT) collision operators is widely used in simulating flow and transport phenomena. The LBM based on two-relaxation-time (TRT) collision operators possesses strengths from the SRT and MRT LBMs, such as its simple implementation and good numerical stability, although tedious mathematical derivations and presentations of the TRT LBM hinder its application to a broad range of flow and transport phenomena. This paper describes the TRT LBM clearly and provides a pseudocode for easy implementation. Various transport phenomena were simulated using the TRT LBM to illustrate its applications in subsurface environments.more » These phenomena include advection-diffusion in uniform flow, Taylor dispersion in a pipe, solute transport in a packed column, reactive transport in uniform flow, and bacterial chemotaxis in porous media. Finally, the TRT LBM demonstrated good numerical performance in terms of accuracy and stability in predicting these transport phenomena. Therefore, the TRT LBM is a powerful tool to simulate various geophysical and biogeochemical processes in subsurface environments.« less

Characterization of Nano-scale Aluminum Oxide Transport through Porous Media

NASA Astrophysics Data System (ADS)

Norwood, S.; Reynolds, M.; Miao, Z.; Brusseau, M. L.; Johnson, G. R.

2011-12-01

Colloidal material (including that in the nanoparticle size range) is naturally present in most subsurface environments. Mobilization of these colloidal materials via particle disaggregation may occur through abrupt changes in flow rate and/or via chemical perturbations, such as rapid changes in ionic strength or solution pH. While concentrations of natural colloidal materials in the subsurface are typically small, those concentrations may be greatly increased at contaminated sites such as following the application of metal oxides for groundwater remediation efforts. Additionally, while land application of biosolids has become common practice in the United States as an alternative to industrial fertilizers, biosolids have been shown to contain a significant fraction of organic and inorganic nano-scale colloidal materials such as oxides of iron, titanium, and aluminum. Given their reactivity and small size, there are many questions concerning the potential migration of nano-scale colloidal materials through the soil column and their potential participation in the facilitated transport of contaminants, such as heavy metals and emerging pollutants. The purpose of this study was to investigate the transport behavior of aluminum oxide (Al2O3) nanoparticles through porous media. The impacts of pH, ionic strength, pore-water velocity (i.e., residence time), and aqueous-phase concentration on transport was investigated. All experiments were conducted with large injection pulses to fully characterize the impact of long-term retention and transport behavior relevant for natural systems wherein multiple retention processes may be operative. The results indicate that the observed nonideal transport behavior of the nano-scale colloids is influenced by multiple retention mechanisms/processes. Given the ubiquitous nature of these nano-scale colloids in the environment, a clear understanding of their transport and fate is necessary in further resolving the potential for facilitated transport of toxins through the subsurface and into our surface and groundwater bodies.

Retention and transport of nutrients in a third-order stream in northwestern California; hyporheic processes

USGS Publications Warehouse

Triska, F.J.; Kennedy, V.C.; Avanzino, R.J.; Zellweger, G.W.; Bencala, K.E.

1989-01-01

Chloride and nitrate were coinjected into the surface waters of a third-order stream for 20 d to exmaine solute retention, and the fate of nitrate during subsurface transport. A series of wells (shallow pits) 0.5-10 m from the adjacent channel were sampled to estimate the lateral interflow of water. Two subsurface return flows beneath the wetted channel were also examined. Results indicated that the capacity of the hyporheic zone for transient solute storage and as potential biological habitat varies with channel morphology, bed roughness, and permeability. A conceptual model that considers the groundwater-stream water interface as the fluvial boundary is proposed. -from Authors

Three-dimensional vapor intrusion modeling approach that combines wind and stack effects on indoor, atmospheric, and subsurface domains.

PubMed

Shirazi, Elham; Pennell, Kelly G

2017-12-13

Vapor intrusion (IV) exposure risks are difficult to characterize due to the role of atmospheric, building and subsurface processes. This study presents a three-dimensional VI model that extends the common subsurface fate and transport equations to incorporate wind and stack effects on indoor air pressure, building air exchange rate (AER) and indoor contaminant concentration to improve VI exposure risk estimates. The model incorporates three modeling programs: (1) COMSOL Multiphysics to model subsurface fate and transport processes, (2) CFD0 to model atmospheric air flow around the building, and (3) CONTAM to model indoor air quality. The combined VI model predicts AER values, zonal indoor air pressures and zonal indoor air contaminant concentrations as a function of wind speed, wind direction and outdoor and indoor temperature. Steady state modeling results for a single-story building with a basement demonstrate that wind speed, wind direction and opening locations in a building play important roles in changing the AER, indoor air pressure, and indoor air contaminant concentration. Calculated indoor air pressures ranged from approximately -10 Pa to +4 Pa depending on weather conditions and building characteristics. AER values, mass entry rates and indoor air concentrations vary depending on weather conditions and building characteristics. The presented modeling approach can be used to investigate the relationship between building features, AER, building pressures, soil gas concentrations, indoor air concentrations and VI exposure risks.

Hyporheic flow and transport processes: mechanisms, models, and biogeochemical implications

USGS Publications Warehouse

Boano, Fulvio; Harvey, Judson W.; Marion, Andrea; Packman, Aaron I.; Revelli, Roberto; Ridolfi, Luca; Anders, Wörman

2014-01-01

Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed."

Hyporheic flow and transport processes: Mechanisms, models, and biogeochemical implications

NASA Astrophysics Data System (ADS)

Boano, F.; Harvey, J. W.; Marion, A.; Packman, A. I.; Revelli, R.; Ridolfi, L.; Wörman, A.

2014-12-01

Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed.

Plant-based plume-scale mapping of tritium contamination in desert soils

USGS Publications Warehouse

Andraski, Brian J.; Stonestrom, David A.; Michel, R.L.; Halford, K.J.; Radyk, J.C.

2005-01-01

Plant-based techniques were tested for field-scale evaluation of tritium contamination adjacent to a low-level radioactive waste (LLRW) facility in the Amargosa Desert, Nevada. Objectives were to (i) characterize and map the spatial variability of tritium in plant water, (ii) develop empirical relations to predict and map subsurface contamination from plant-water concentrations, and (iii) gain insight into tritium migration pathways and processes. Plant sampling [creosote bush, Larrea tridentata (Sessé & Moc. ex DC.) Coville] required one-fifth the time of soil water vapor sampling. Plant concentrations were spatially correlated to a separation distance of 380 m; measurement uncertainty accounted for <0.1% of the total variability in the data. Regression equations based on plant tritium explained 96 and 90% of the variation in root-zone and sub-root-zone soil water vapor concentrations, respectively. The equations were combined with kriged plant-water concentrations to map subsurface contamination. Mapping showed preferential lateral movement of tritium through a dry, coarse-textured layer beneath the root zone, with concurrent upward movement through the root zone. Analysis of subsurface fluxes along a transect perpendicular to the LLRW facility showed that upward diffusive-vapor transport dominates other transport modes beneath native vegetation. Downward advective-liquid transport dominates at one endpoint of the transect, beneath a devegetated road immediately adjacent to the facility. To our knowledge, this study is the first to document large-scale subsurface vapor-phase tritium migration from a LLRW facility. Plant-based methods provide a noninvasive, cost-effective approach to mapping subsurface tritium migration in desert areas.

MOBILIZATION AND CHARACTERIZATION OF COLLOIDS GENERATED FROM CEMENT LEACHATES MOVING THROUGH A SRS SANDY SEDIMENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, D.; Roberts, K.; Kaplan, D.

Naturally occurring mobile colloids are ubiquitous and are involved in many important processes in the subsurface zone. For example, colloid generation and subsequent mobilization represent a possible mechanism for the transport of contaminants including radionuclides in the subsurface environments. For colloid-facilitated transport to be significant, three criteria must be met: (1) colloids must be generated; (2) contaminants must associate with the colloids preferentially to the immobile solid phase (aquifer); and (3) colloids must be transported through the groundwater or in subsurface environments - once these colloids start moving they become 'mobile colloids'. Although some experimental investigations of particle release inmore » natural porous media have been conducted, the detailed mechanisms of release and re-deposition of colloidal particles within natural porous media are poorly understood. Even though this vector of transport is known, the extent of its importance is not known yet. Colloid-facilitated transport of trace radionuclides has been observed in the field, thus demonstrating a possible radiological risk associated with the colloids. The objective of this study was to determine if cementitious leachate would promote the in situ mobilization of natural colloidal particles from a SRS sandy sediment. The intent was to determine whether cementitious surface or subsurface structure would create plumes that could produce conditions conducive to sediment dispersion and mobile colloid generation. Column studies were conducted and the cation chemistries of influents and effluents were analyzed by ICP-OES, while the mobilized colloids were characterized using XRD, SEM, EDX, PSD and Zeta potential. The mobilization mechanisms of colloids in a SRS sandy sediment by cement leachates were studied.« less

Physical controls and predictability of stream hyporheic flow evaluated with a multiscale model

USGS Publications Warehouse

Stonedahl, Susa H.; Harvey, Judson W.; Detty, Joel; Aubeneau, Antoine; Packman, Aaron I.

2012-01-01

Improved predictions of hyporheic exchange based on easily measured physical variables are needed to improve assessment of solute transport and reaction processes in watersheds. Here we compare physically based model predictions for an Indiana stream with stream tracer results interpreted using the Transient Storage Model (TSM). We parameterized the physically based, Multiscale Model (MSM) of stream-groundwater interactions with measured stream planform and discharge, stream velocity, streambed hydraulic conductivity and porosity, and topography of the streambed at distinct spatial scales (i.e., ripple, bar, and reach scales). We predicted hyporheic exchange fluxes and hyporheic residence times using the MSM. A Continuous Time Random Walk (CTRW) model was used to convert the MSM output into predictions of in stream solute transport, which we compared with field observations and TSM parameters obtained by fitting solute transport data. MSM simulations indicated that surface-subsurface exchange through smaller topographic features such as ripples was much faster than exchange through larger topographic features such as bars. However, hyporheic exchange varies nonlinearly with groundwater discharge owing to interactions between flows induced at different topographic scales. MSM simulations showed that groundwater discharge significantly decreased both the volume of water entering the subsurface and the time it spent in the subsurface. The MSM also characterized longer timescales of exchange than were observed by the tracer-injection approach. The tracer data, and corresponding TSM fits, were limited by tracer measurement sensitivity and uncertainty in estimates of background tracer concentrations. Our results indicate that rates and patterns of hyporheic exchange are strongly influenced by a continuum of surface-subsurface hydrologic interactions over a wide range of spatial and temporal scales rather than discrete processes.

Transport and Retention of Concentrated Oil-in-Water Emulsions in Sandy Porous Media

NASA Astrophysics Data System (ADS)

Muller, K.; Esahani, S. G.; Steven, C. C.; Ramsburg, A.

2015-12-01

Oil-in-water emulsions are widely employed to promote biotic reduction of contaminants; however, emulsions can also be used to encapsulate and deliver active ingredients required for long-term subsurface treatment. Our research focuses on encapsulating alkalinity-releasing particles in oil-in-water emulsions for sustained control of subsurface pH. Typical characteristics of these emulsions include kinetically stable for >20 hr; 20% soybean oil; 1 g/mL density; 8-10 cP viscosity; and 1.5 μm droplet d50, with emulsions developed for favorable subsurface delivery. The viscosity of the oil-in-water emulsions was found to be a function of oil content. Ultimately we aim to model both emulsion delivery and alkalinity release (from retained emulsion droplets) to provide a description of pH treatment. Emulsion transport and retention was investigated via a series of 1-d column experiments using varying particle size fractions of Ottawa sand. Emulsions were introduced for approximately two pore volumes followed by a flush of background solution (approx. ρ=1 g/mL; μ=1cP). Emulsion breakthrough curves exhibit an early fall on the backside of the breakthrough curve along with tailing. Deposition profiles are found to be hyper-exponential and unaffected by extended periods of background flow. Particle transport models established for dilute suspensions are unable to describe the transport of the concentrated emulsions considered here. Thus, we explore the relative importance of additional processes driving concentrated droplet transport and retention. Focus is placed on evaluating the role of attachment-detachment-straining processes, as well as the influence of mixing from both viscous instabilities and variable water saturation due to deposited mass.

Seasonal load restriction tool : Clarus regional demonstrations.

DOT National Transportation Integrated Search

2011-01-01

State transportation agencies have wanted to improve : the techniques that lead to the decisions to impose and : subsequently lift restrictions on selected roads that are prone : to road damage due to subsurface freezing/thawing processes. : The Seas...

Sediment detachment and transport processes associated with internal erosion of soil pipes: Often overlooked processes of gully erosion

USDA-ARS?s Scientific Manuscript database

Subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping. The development of perched water tables...

Comparison of measured and simulated concentrations of 133Xe in the shallow subsurface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Christine M.; Biegalski, Steven R.; Lowre

2018-09-01

Radioactive isotopes of the noble gases xenon and argon are considered primary indicators of an underground nuclear explosion. However, high atmospheric concentrations from other anthropogenic sources may lead to an elevation in the underground levels of these gases, particularly in times of increasing atmospheric pressure. In 2014, a week long sampling campaign near Canadian Nuclear Laboratories in the Ottawa River Valley resulted in first of their kind measurements of atmospheric 133Xe that had been pressed into the subsurface. In an effort to better understand this imprinting process, a second follow-up sampling campaign was conducted in the same location in 2016.more » The results of the second sampling campaign, where samples were collected at depths of 1 and 2 meters over a 14 day period and measured for their 133Xe concentration, are presented here. Gas transport and sample concentrations were predicted using the Subsurface Transport over Multiple Phases (STOMP) simulator. These results are examined and compared to the corresponding experimental results.« less

Comparison of measured and simulated concentrations of 133 Xe in the shallow subsurface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, C.; Biegalski, S. R.; Lowrey, J. D.

Radioactive isotopes of the noble gases xenon and argon are considered primary indicators of an underground nuclear explosion. However, high atmospheric concentrations from other anthropogenic sources may lead to an elevation in the underground levels of these gases, particularly in times of increasing atmospheric pressure. In 2014, a week long sampling campaign near Canadian Nuclear Laboratories in the Ottawa River Valley resulted in first of their kind measurements of atmospheric 133Xe that had been pressed into the subsurface. In an effort to better understand this imprinting process, a second follow-up sampling campaign was conducted in the same location in 2016.more » The results of the second sampling campaign, where samples were collected at depths of 1 and 2 meters over a 14 day period and measured for their 133Xe concentration, are presented here. Gas transport and sample concentrations were predicted using the Subsurface Transport over Multiple Phases (STOMP) simulator. These results are examined and compared to the corresponding experimental results.« less

PFLOTRAN-E4D: A parallel open source PFLOTRAN module for simulating time-lapse electrical resistivity data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Timothy C.; Hammond, Glenn E.; Chen, Xingyuan

Time-lapse electrical resistivity tomography (ERT) is finding increased application for remotely monitoring processes occurring in the near subsurface in three-dimensions (i.e. 4D monitoring). However, there are few codes capable of simulating the evolution of subsurface resistivity and corresponding tomographic measurements arising from a particular process, particularly in parallel and with an open source license. Herein we describe and demonstrate an electrical resistivity tomography module for the PFLOTRAN subsurface flow and reactive transport simulation code, named PFLOTRAN-E4D. The PFLOTRAN-E4D module operates in parallel using a dedicated set of compute cores in a master-slave configuration. At each time step, the master processesmore » receives subsurface states from PFLOTRAN, converts those states to bulk electrical conductivity, and instructs the slave processes to simulate a tomographic data set. The resulting multi-physics simulation capability enables accurate feasibility studies for ERT imaging, the identification of the ERT signatures that are unique to a given process, and facilitates the joint inversion of ERT data with hydrogeological data for subsurface characterization. PFLOTRAN-E4D is demonstrated herein using a field study of stage-driven groundwater/river water interaction ERT monitoring along the Columbia River, Washington, USA. Results demonstrate the complex nature of subsurface electrical conductivity changes, in both the saturated and unsaturated zones, arising from river stage fluctuations and associated river water intrusion into the aquifer. Furthermore, the results also demonstrate the sensitivity of surface based ERT measurements to those changes over time.« less

PFLOTRAN-E4D: A parallel open source PFLOTRAN module for simulating time-lapse electrical resistivity data

DOE PAGES

Johnson, Timothy C.; Hammond, Glenn E.; Chen, Xingyuan

2016-09-22

Time-lapse electrical resistivity tomography (ERT) is finding increased application for remotely monitoring processes occurring in the near subsurface in three-dimensions (i.e. 4D monitoring). However, there are few codes capable of simulating the evolution of subsurface resistivity and corresponding tomographic measurements arising from a particular process, particularly in parallel and with an open source license. Herein we describe and demonstrate an electrical resistivity tomography module for the PFLOTRAN subsurface flow and reactive transport simulation code, named PFLOTRAN-E4D. The PFLOTRAN-E4D module operates in parallel using a dedicated set of compute cores in a master-slave configuration. At each time step, the master processesmore » receives subsurface states from PFLOTRAN, converts those states to bulk electrical conductivity, and instructs the slave processes to simulate a tomographic data set. The resulting multi-physics simulation capability enables accurate feasibility studies for ERT imaging, the identification of the ERT signatures that are unique to a given process, and facilitates the joint inversion of ERT data with hydrogeological data for subsurface characterization. PFLOTRAN-E4D is demonstrated herein using a field study of stage-driven groundwater/river water interaction ERT monitoring along the Columbia River, Washington, USA. Results demonstrate the complex nature of subsurface electrical conductivity changes, in both the saturated and unsaturated zones, arising from river stage fluctuations and associated river water intrusion into the aquifer. Furthermore, the results also demonstrate the sensitivity of surface based ERT measurements to those changes over time.« less

Impacts of microtopographic snow redistribution and lateral subsurface processes on hydrologic and thermal states in an Arctic polygonal ground ecosystem: a case study using ELM-3D v1.0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bisht, Gautam; Riley, William J.; Wainwright, Haruko M.

Microtopographic features, such as polygonal ground, are characteristic sources of landscape heterogeneity in the Alaskan Arctic coastal plain. In this study, we analyze the effects of snow redistribution (SR) and lateral subsurface processes on hydrologic and thermal states at a polygonal tundra site near Barrow, Alaska. We extended the land model integrated in the E3SM to redistribute incoming snow by accounting for microtopography and incorporated subsurface lateral transport of water and energy (ELM-3D v1.0). Multiple 10-year-long simulations were performed for a transect across a polygonal tundra landscape at the Barrow Environmental Observatory in Alaska to isolate the impact of SRmore » and subsurface process representation. When SR was included, model predictions better agreed (higher R 2, lower bias and RMSE) with observed differences in snow depth between polygonal rims and centers. The model was also able to accurately reproduce observed soil temperature vertical profiles in the polygon rims and centers (overall bias, RMSE, and R 2 of 0.59°C, 1.82°C, and 0.99, respectively). The spatial heterogeneity of snow depth during the winter due to SR generated surface soil temperature heterogeneity that propagated in depth and time and led to ~ 10 cm shallower and ~ 5 cm deeper maximum annual thaw depths under the polygon rims and centers, respectively. Additionally, SR led to spatial heterogeneity in surface energy fluxes and soil moisture during the summer. Excluding lateral subsurface hydrologic and thermal processes led to small effects on mean states but an overestimation of spatial variability in soil moisture and soil temperature as subsurface liquid pressure and thermal gradients were artificially prevented from spatially dissipating over time. The effect of lateral subsurface processes on maximum thaw depths was modest, with mean absolute differences of ~ 3 cm. Our integration of three-dimensional subsurface hydrologic and thermal subsurface dynamics in the E3SM land model will facilitate a wide range of analyses heretofore impossible in an ESM context.« less

Impacts of microtopographic snow redistribution and lateral subsurface processes on hydrologic and thermal states in an Arctic polygonal ground ecosystem: a case study using ELM-3D v1.0

DOE PAGES

Bisht, Gautam; Riley, William J.; Wainwright, Haruko M.; ...

2018-01-08

Microtopographic features, such as polygonal ground, are characteristic sources of landscape heterogeneity in the Alaskan Arctic coastal plain. In this study, we analyze the effects of snow redistribution (SR) and lateral subsurface processes on hydrologic and thermal states at a polygonal tundra site near Barrow, Alaska. We extended the land model integrated in the E3SM to redistribute incoming snow by accounting for microtopography and incorporated subsurface lateral transport of water and energy (ELM-3D v1.0). Multiple 10-year-long simulations were performed for a transect across a polygonal tundra landscape at the Barrow Environmental Observatory in Alaska to isolate the impact of SRmore » and subsurface process representation. When SR was included, model predictions better agreed (higher R 2, lower bias and RMSE) with observed differences in snow depth between polygonal rims and centers. The model was also able to accurately reproduce observed soil temperature vertical profiles in the polygon rims and centers (overall bias, RMSE, and R 2 of 0.59°C, 1.82°C, and 0.99, respectively). The spatial heterogeneity of snow depth during the winter due to SR generated surface soil temperature heterogeneity that propagated in depth and time and led to ~ 10 cm shallower and ~ 5 cm deeper maximum annual thaw depths under the polygon rims and centers, respectively. Additionally, SR led to spatial heterogeneity in surface energy fluxes and soil moisture during the summer. Excluding lateral subsurface hydrologic and thermal processes led to small effects on mean states but an overestimation of spatial variability in soil moisture and soil temperature as subsurface liquid pressure and thermal gradients were artificially prevented from spatially dissipating over time. The effect of lateral subsurface processes on maximum thaw depths was modest, with mean absolute differences of ~ 3 cm. Our integration of three-dimensional subsurface hydrologic and thermal subsurface dynamics in the E3SM land model will facilitate a wide range of analyses heretofore impossible in an ESM context.« less

Impacts of microtopographic snow redistribution and lateral subsurface processes on hydrologic and thermal states in an Arctic polygonal ground ecosystem: a case study using ELM-3D v1.0

NASA Astrophysics Data System (ADS)

Bisht, Gautam; Riley, William J.; Wainwright, Haruko M.; Dafflon, Baptiste; Yuan, Fengming; Romanovsky, Vladimir E.

2018-01-01

Microtopographic features, such as polygonal ground, are characteristic sources of landscape heterogeneity in the Alaskan Arctic coastal plain. Here, we analyze the effects of snow redistribution (SR) and lateral subsurface processes on hydrologic and thermal states at a polygonal tundra site near Barrow, Alaska. We extended the land model integrated in the E3SM to redistribute incoming snow by accounting for microtopography and incorporated subsurface lateral transport of water and energy (ELM-3D v1.0). Multiple 10-year-long simulations were performed for a transect across a polygonal tundra landscape at the Barrow Environmental Observatory in Alaska to isolate the impact of SR and subsurface process representation. When SR was included, model predictions better agreed (higher R2, lower bias and RMSE) with observed differences in snow depth between polygonal rims and centers. The model was also able to accurately reproduce observed soil temperature vertical profiles in the polygon rims and centers (overall bias, RMSE, and R2 of 0.59 °C, 1.82 °C, and 0.99, respectively). The spatial heterogeneity of snow depth during the winter due to SR generated surface soil temperature heterogeneity that propagated in depth and time and led to ˜ 10 cm shallower and ˜ 5 cm deeper maximum annual thaw depths under the polygon rims and centers, respectively. Additionally, SR led to spatial heterogeneity in surface energy fluxes and soil moisture during the summer. Excluding lateral subsurface hydrologic and thermal processes led to small effects on mean states but an overestimation of spatial variability in soil moisture and soil temperature as subsurface liquid pressure and thermal gradients were artificially prevented from spatially dissipating over time. The effect of lateral subsurface processes on maximum thaw depths was modest, with mean absolute differences of ˜ 3 cm. Our integration of three-dimensional subsurface hydrologic and thermal subsurface dynamics in the E3SM land model will facilitate a wide range of analyses heretofore impossible in an ESM context.

A composite numerical model for assessing subsurface transport of oily wastes and chemical constituents

NASA Astrophysics Data System (ADS)

Panday, S.; Wu, Y. S.; Huyakorn, P. S.; Wade, S. C.; Saleem, Z. A.

1997-02-01

Subsurface fate and transport models are utilized to predict concentrations of chemicals leaching from wastes into downgradient receptor wells. The contaminant concentrations in groundwater provide a measure of the risk to human health and the environment. The level of potential risk is currently used by the U.S. Environmental Protection Agency to determine whether management of the wastes should conform to hazardous waste management standards. It is important that the transport and fate of contaminants is simulated realistically. Most models in common use are inappropriate for simulating the migration of wastes containing significant fractions of nonaqueous-phase liquids (NAPLs). The migration of NAPL and its dissolved constituents may not be reliably predicted using conventional aqueous-phase transport simulations. To overcome this deficiency, an efficient and robust regulatory assessment model incorporating multiphase flow and transport in the unsaturated and saturated zones of the subsurface environment has been developed. The proposed composite model takes into account all of the major transport processes including infiltration and ambient flow of NAPL, entrapment of residual NAPL, adsorption, volatilization, degradation, dissolution of chemical constituents, and transport by advection and hydrodynamic dispersion. Conceptually, the subsurface is treated as a composite unsaturated zone-saturated zone system. The composite simulator consists of three major interconnected computational modules representing the following components of the migration pathway: (1) vertical multiphase flow and transport in the unsaturated zone; (2) areal movement of the free-product lens in the saturated zone with vertical equilibrium; and (3) three-dimensional aqueous-phase transport of dissolved chemicals in ambient groundwater. Such a composite model configuration promotes computational efficiency and robustness (desirable for regulatory assessment applications). Two examples are presented to demonstrate the model verification and a site application. Simulation results obtained using the composite modeling approach are compared with a rigorous numerical solution and field observations of crude oil saturations and plume concentrations of total dissolved organic carbon at a spill site in Minnesota, U.S.A. These comparisons demonstrate the ability of the present model to provide realistic depiction of field-scale situations.

Optimization of subsurface flow and associated treatment processes.

DOT National Transportation Integrated Search

2006-02-01

The Louisiana Department of Transportation and Development has long been interested in low maintenance waste treatment systems that can be used to treat small flows in situations where skilled operators are not available. The purpose of this project ...

PFLOTRAN-E4D: A parallel open source PFLOTRAN module for simulating time-lapse electrical resistivity data

NASA Astrophysics Data System (ADS)

Johnson, Timothy C.; Hammond, Glenn E.; Chen, Xingyuan

2017-02-01

Time-lapse electrical resistivity tomography (ERT) is finding increased application for remotely monitoring processes occurring in the near subsurface in three-dimensions (i.e. 4D monitoring). However, there are few codes capable of simulating the evolution of subsurface resistivity and corresponding tomographic measurements arising from a particular process, particularly in parallel and with an open source license. Herein we describe and demonstrate an electrical resistivity tomography module for the PFLOTRAN subsurface flow and reactive transport simulation code, named PFLOTRAN-E4D. The PFLOTRAN-E4D module operates in parallel using a dedicated set of compute cores in a master-slave configuration. At each time step, the master processes receives subsurface states from PFLOTRAN, converts those states to bulk electrical conductivity, and instructs the slave processes to simulate a tomographic data set. The resulting multi-physics simulation capability enables accurate feasibility studies for ERT imaging, the identification of the ERT signatures that are unique to a given process, and facilitates the joint inversion of ERT data with hydrogeological data for subsurface characterization. PFLOTRAN-E4D is demonstrated herein using a field study of stage-driven groundwater/river water interaction ERT monitoring along the Columbia River, Washington, USA. Results demonstrate the complex nature of subsurface electrical conductivity changes, in both the saturated and unsaturated zones, arising from river stage fluctuations and associated river water intrusion into the aquifer. The results also demonstrate the sensitivity of surface based ERT measurements to those changes over time. PFLOTRAN-E4D is available with the PFLOTRAN development version with an open-source license at https://bitbucket.org/pflotran/pflotran-dev.

Experimental quantification of solute transport through the vadose zone under dynamic boundary conditions with dye tracers and optical methods.

NASA Astrophysics Data System (ADS)

Cremer, Clemens; Neuweiler, Insa

2017-04-01

Knowledge of subsurface solute transport processes is vital to investigate e.g. groundwater contamination, nutrient uptake by plant roots and to implement remediation strategies. Beside field measurements and numerical simulations, physical laboratory experiments represent a way to establish process understanding and furthermore validate numerical schemes. Atmospheric forcings, such as erratically varying infiltration and evaporation cycles, subject the shallow subsurface to local and temporal variations in water content and associated hydraulic conductivity of the prevailing porous media. Those variations in material properties can cause flow paths to differ between upward and downward flow periods. Thereby, the unsaturated subsurface presents a highly complicated, dynamic system. Following an extensive systematical numerical investigation of flow and transport through bimodal, unsaturated porous media under dynamic boundary conditions (Cremer et al., 2016), we conduct physical laboratory experiments in a 22 cm x 8 cm x 1 cm flow cell where we introduce structural heterogeneity in the form sharp material interfaces between different porous media. In all experiments, a constant pressure head is implemented at the lower boundary, while cyclic infiltration-evaporation phases are applied at the soil surface. As a reference case a stationary infiltration with a rate corresponding to the cycle-averaged infiltration rate is applied. By initial application of dye tracers, solute transport within the domain is visualized such that transport paths and redistribution processes can be observed in a qualitative manner. Solute leaching is quantified at the bottom outlet, where breakthrough curves are obtained via spectroscopy. Liquid and vapor flow in and out of the domain is obtained from multiple balances. Thereby, the interplay of material structural heterogeneity and alternating flow (transport) directions and flow (transport) paths is investigated. Results show lateral transport through the material interface which differs between the stationary (unilateral) and dynamic cases (bilateral). This qualitative observation is confirmed by breakthrough curves for dynamic experiments which generally show the trend of faster initial breakthrough and increased tailing when compared to stationary infiltration results. Literature Cremer, C.J.M., I. Neuweiler, M. Bechtold, J. Vanderborght (2016): Solute Transport in Heterogeneous Soil with Time-Dependent Boundary Conditions, Vadose Zone Journal 15 (6) DOI: 10.2136/vzj2015.11.0144

MODELING THREE-DIMENSIONAL SUBSURFACE FLOW, FATE AND TRANSPORT OF MICROBES AND CHEMICALS (3DFATMIC)

EPA Science Inventory

A three-dimensional model simulating the subsurface flow, microbial growth and degradation, microbial-chemical reaction, and transport of microbes and chemicals has been developed. he model is designed to solve the coupled flow and transport equations. asically, the saturated-uns...

Effect of flow on bacterial transport and biofilm formation in saturated porous media

NASA Astrophysics Data System (ADS)

Rusconi, R.

2016-12-01

Understanding the transport of bacteria in saturated porous media is crucial for many applications ranging from the management of pumping wells subject to bio-clogging to the design of new bioremediation schemes for subsurface contamination. However, little is known about the spatial distribution of bacteria at the pore scale, particularly when small-scale heterogeneities - always present even in seemingly homogeneous aquifers - lead to preferential pathways for groundwater flow. In particular, the coupling of flow and motility has recently been shown to strongly affect bacterial transport1, and this leads us to predict that subsurface flow may strongly affect the dispersal of bacteria and the formation of biofilms in saturated aquifers. I present here microfluidic experiments combined with numerical simulations to show how the topological features of the flow correlate with bacterial concentration and promote the attachment of bacteria to specific regions of the pore network, which will ultimately influence the formations of biofilms. These results highlight the intimate link between small-scale biological processes and transport in porous media.

Assessing conceptual models for subsurface reactive transport of inorganic contaminants

USGS Publications Warehouse

Davis, James A.; Yabusaki, Steven B.; Steefel, Carl; Zachara, John M.; Curtis, Gary P.; Redden, George D.; Criscenti, Louise J.; Honeyman, Bruce D.

2004-01-01

In many subsurface situations where human health and environmental quality are at risk (e.g., contaminant hydrogeology petroleum extraction, carbon sequestration, etc.),scientists and engineers are being asked by federal agency decision-makers to predict the fate of chemical species under conditions where both reactions and transport are processes of first-order importance.In 2002, a working group (WG) was formed by representatives of the U.S. Geological Survey, Environmental Protection Agency, Department of Energy Nuclear Regulatory Commission, Department of Agriculture, and Army Engineer Research and Development Center to assess the role of reactive transport modeling (RTM) in addressing these situations. Specifically the goals of the WG are to (1) evaluate the state of the art in conceptual model development and parameterization for RTM, as applied to soil,vadose zone, and groundwater systems, and (2) prioritize research directions that would enhance the practical utility of RTM.

A stochastic approach for model reduction and memory function design in hydrogeophysical inversion

NASA Astrophysics Data System (ADS)

Hou, Z.; Kellogg, A.; Terry, N.

2009-12-01

Geophysical (e.g., seismic, electromagnetic, radar) techniques and statistical methods are essential for research related to subsurface characterization, including monitoring subsurface flow and transport processes, oil/gas reservoir identification, etc. For deep subsurface characterization such as reservoir petroleum exploration, seismic methods have been widely used. Recently, electromagnetic (EM) methods have drawn great attention in the area of reservoir characterization. However, considering the enormous computational demand corresponding to seismic and EM forward modeling, it is usually a big problem to have too many unknown parameters in the modeling domain. For shallow subsurface applications, the characterization can be very complicated considering the complexity and nonlinearity of flow and transport processes in the unsaturated zone. It is warranted to reduce the dimension of parameter space to a reasonable level. Another common concern is how to make the best use of time-lapse data with spatial-temporal correlations. This is even more critical when we try to monitor subsurface processes using geophysical data collected at different times. The normal practice is to get the inverse images individually. These images are not necessarily continuous or even reasonably related, because of the non-uniqueness of hydrogeophysical inversion. We propose to use a stochastic framework by integrating minimum-relative-entropy concept, quasi Monto Carlo sampling techniques, and statistical tests. The approach allows efficient and sufficient exploration of all possibilities of model parameters and evaluation of their significances to geophysical responses. The analyses enable us to reduce the parameter space significantly. The approach can be combined with Bayesian updating, allowing us to treat the updated ‘posterior’ pdf as a memory function, which stores all the information up to date about the distributions of soil/field attributes/properties, then consider the memory function as a new prior and generate samples from it for further updating when more geophysical data is available. We applied this approach for deep oil reservoir characterization and for shallow subsurface flow monitoring. The model reduction approach reliably helps reduce the joint seismic/EM/radar inversion computational time to reasonable levels. Continuous inversion images are obtained using time-lapse data with the “memory function” applied in the Bayesian inversion.

Coupling a three-dimensional subsurface flow and transport model with a land surface model to simulate stream-aquifer-land interactions (CP v1.0)

NASA Astrophysics Data System (ADS)

Bisht, Gautam; Huang, Maoyi; Zhou, Tian; Chen, Xingyuan; Dai, Heng; Hammond, Glenn E.; Riley, William J.; Downs, Janelle L.; Liu, Ying; Zachara, John M.

2017-12-01

A fully coupled three-dimensional surface and subsurface land model is developed and applied to a site along the Columbia River to simulate three-way interactions among river water, groundwater, and land surface processes. The model features the coupling of the Community Land Model version 4.5 (CLM4.5) and a massively parallel multiphysics reactive transport model (PFLOTRAN). The coupled model, named CP v1.0, is applied to a 400 m × 400 m study domain instrumented with groundwater monitoring wells along the Columbia River shoreline. CP v1.0 simulations are performed at three spatial resolutions (i.e., 2, 10, and 20 m) over a 5-year period to evaluate the impact of hydroclimatic conditions and spatial resolution on simulated variables. Results show that the coupled model is capable of simulating groundwater-river-water interactions driven by river stage variability along managed river reaches, which are of global significance as a result of over 30 000 dams constructed worldwide during the past half-century. Our numerical experiments suggest that the land-surface energy partitioning is strongly modulated by groundwater-river-water interactions through expanding the periodically inundated fraction of the riparian zone, and enhancing moisture availability in the vadose zone via capillary rise in response to the river stage change. Meanwhile, CLM4.5 fails to capture the key hydrologic process (i.e., groundwater-river-water exchange) at the site, and consequently simulates drastically different water and energy budgets. Furthermore, spatial resolution is found to significantly impact the accuracy of estimated the mass exchange rates at the boundaries of the aquifer, and it becomes critical when surface and subsurface become more tightly coupled with groundwater table within 6 to 7 meters below the surface. Inclusion of lateral subsurface flow influenced both the surface energy budget and subsurface transport processes as a result of river-water intrusion into the subsurface in response to an elevated river stage that increased soil moisture for evapotranspiration and suppressed available energy for sensible heat in the warm season. The coupled model developed in this study can be used for improving mechanistic understanding of ecosystem functioning and biogeochemical cycling along river corridors under historical and future hydroclimatic changes. The dataset presented in this study can also serve as a good benchmarking case for testing other integrated models.

Coupling a three-dimensional subsurface flow and transport model with a land surface model to simulate stream–aquifer–land interactions (CP v1.0)

DOE PAGES

Bisht, Gautam; Huang, Maoyi; Zhou, Tian; ...

2017-12-12

A fully coupled three-dimensional surface and subsurface land model is developed and applied to a site along the Columbia River to simulate three-way interactions among river water, groundwater, and land surface processes. The model features the coupling of the Community Land Model version 4.5 (CLM4.5) and a massively parallel multiphysics reactive transport model (PFLOTRAN). The coupled model, named CP v1.0, is applied to a 400 m × 400 m study domain instrumented with groundwater monitoring wells along the Columbia River shoreline. CP v1.0 simulations are performed at three spatial resolutions (i.e., 2, 10, and 20 m) over a 5-year periodmore » to evaluate the impact of hydroclimatic conditions and spatial resolution on simulated variables. Results show that the coupled model is capable of simulating groundwater–river-water interactions driven by river stage variability along managed river reaches, which are of global significance as a result of over 30 000 dams constructed worldwide during the past half-century. Our numerical experiments suggest that the land-surface energy partitioning is strongly modulated by groundwater–river-water interactions through expanding the periodically inundated fraction of the riparian zone, and enhancing moisture availability in the vadose zone via capillary rise in response to the river stage change. Meanwhile, CLM4.5 fails to capture the key hydrologic process (i.e., groundwater–river-water exchange) at the site, and consequently simulates drastically different water and energy budgets. Furthermore, spatial resolution is found to significantly impact the accuracy of estimated the mass exchange rates at the boundaries of the aquifer, and it becomes critical when surface and subsurface become more tightly coupled with groundwater table within 6 to 7 meters below the surface. Inclusion of lateral subsurface flow influenced both the surface energy budget and subsurface transport processes as a result of river-water intrusion into the subsurface in response to an elevated river stage that increased soil moisture for evapotranspiration and suppressed available energy for sensible heat in the warm season. The coupled model developed in this study can be used for improving mechanistic understanding of ecosystem functioning and biogeochemical cycling along river corridors under historical and future hydroclimatic changes. The dataset presented in this study can also serve as a good benchmarking case for testing other integrated models.« less

Coupling a three-dimensional subsurface flow and transport model with a land surface model to simulate stream–aquifer–land interactions (CP v1.0)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bisht, Gautam; Huang, Maoyi; Zhou, Tian

A fully coupled three-dimensional surface and subsurface land model is developed and applied to a site along the Columbia River to simulate three-way interactions among river water, groundwater, and land surface processes. The model features the coupling of the Community Land Model version 4.5 (CLM4.5) and a massively parallel multiphysics reactive transport model (PFLOTRAN). The coupled model, named CP v1.0, is applied to a 400 m × 400 m study domain instrumented with groundwater monitoring wells along the Columbia River shoreline. CP v1.0 simulations are performed at three spatial resolutions (i.e., 2, 10, and 20 m) over a 5-year period to evaluate themore » impact of hydroclimatic conditions and spatial resolution on simulated variables. Results show that the coupled model is capable of simulating groundwater–river-water interactions driven by river stage variability along managed river reaches, which are of global significance as a result of over 30 000 dams constructed worldwide during the past half-century. Our numerical experiments suggest that the land-surface energy partitioning is strongly modulated by groundwater–river-water interactions through expanding the periodically inundated fraction of the riparian zone, and enhancing moisture availability in the vadose zone via capillary rise in response to the river stage change. Meanwhile, CLM4.5 fails to capture the key hydrologic process (i.e., groundwater–river-water exchange) at the site, and consequently simulates drastically different water and energy budgets. Furthermore, spatial resolution is found to significantly impact the accuracy of estimated the mass exchange rates at the boundaries of the aquifer, and it becomes critical when surface and subsurface become more tightly coupled with groundwater table within 6 to 7 meters below the surface. Inclusion of lateral subsurface flow influenced both the surface energy budget and subsurface transport processes as a result of river-water intrusion into the subsurface in response to an elevated river stage that increased soil moisture for evapotranspiration and suppressed available energy for sensible heat in the warm season. The coupled model developed in this study can be used for improving mechanistic understanding of ecosystem functioning and biogeochemical cycling along river corridors under historical and future hydroclimatic changes. The dataset presented in this study can also serve as a good benchmarking case for testing other integrated models.« less

Coupling a three-dimensional subsurface flow and transport model with a land surface model to simulate stream–aquifer–land interactions (CP v1.0)

DOE PAGES

Bisht, Gautam; Huang, Maoyi; Zhou, Tian; ...

2017-01-01

A fully coupled three-dimensional surface and subsurface land model is developed and applied to a site along the Columbia River to simulate three-way interactions among river water, groundwater, and land surface processes. The model features the coupling of the Community Land Model version 4.5 (CLM4.5) and a massively parallel multiphysics reactive transport model (PFLOTRAN). The coupled model, named CP v1.0, is applied to a 400 m × 400 m study domain instrumented with groundwater monitoring wells along the Columbia River shoreline. CP v1.0 simulations are performed at three spatial resolutions (i.e., 2, 10, and 20 m) over a 5-year period to evaluate themore » impact of hydroclimatic conditions and spatial resolution on simulated variables. Results show that the coupled model is capable of simulating groundwater–river-water interactions driven by river stage variability along managed river reaches, which are of global significance as a result of over 30 000 dams constructed worldwide during the past half-century. Our numerical experiments suggest that the land-surface energy partitioning is strongly modulated by groundwater–river-water interactions through expanding the periodically inundated fraction of the riparian zone, and enhancing moisture availability in the vadose zone via capillary rise in response to the river stage change. Meanwhile, CLM4.5 fails to capture the key hydrologic process (i.e., groundwater–river-water exchange) at the site, and consequently simulates drastically different water and energy budgets. Furthermore, spatial resolution is found to significantly impact the accuracy of estimated the mass exchange rates at the boundaries of the aquifer, and it becomes critical when surface and subsurface become more tightly coupled with groundwater table within 6 to 7 meters below the surface. Inclusion of lateral subsurface flow influenced both the surface energy budget and subsurface transport processes as a result of river-water intrusion into the subsurface in response to an elevated river stage that increased soil moisture for evapotranspiration and suppressed available energy for sensible heat in the warm season. The coupled model developed in this study can be used for improving mechanistic understanding of ecosystem functioning and biogeochemical cycling along river corridors under historical and future hydroclimatic changes. The dataset presented in this study can also serve as a good benchmarking case for testing other integrated models.« less

Coupling a three-dimensional subsurface flow and transport model with a land surface model to simulate stream–aquifer–land interactions (CP v1.0)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bisht, Gautam; Huang, Maoyi; Zhou, Tian

A fully coupled three-dimensional surface and subsurface land model is developed and applied to a site along the Columbia River to simulate three-way interactions among river water, groundwater, and land surface processes. The model features the coupling of the Community Land Model version 4.5 (CLM4.5) and a massively parallel multiphysics reactive transport model (PFLOTRAN). The coupled model, named CP v1.0, is applied to a 400 m × 400 m study domain instrumented with groundwater monitoring wells along the Columbia River shoreline. CP v1.0 simulations are performed at three spatial resolutions (i.e., 2, 10, and 20 m) over a 5-year periodmore » to evaluate the impact of hydroclimatic conditions and spatial resolution on simulated variables. Results show that the coupled model is capable of simulating groundwater–river-water interactions driven by river stage variability along managed river reaches, which are of global significance as a result of over 30 000 dams constructed worldwide during the past half-century. Our numerical experiments suggest that the land-surface energy partitioning is strongly modulated by groundwater–river-water interactions through expanding the periodically inundated fraction of the riparian zone, and enhancing moisture availability in the vadose zone via capillary rise in response to the river stage change. Meanwhile, CLM4.5 fails to capture the key hydrologic process (i.e., groundwater–river-water exchange) at the site, and consequently simulates drastically different water and energy budgets. Furthermore, spatial resolution is found to significantly impact the accuracy of estimated the mass exchange rates at the boundaries of the aquifer, and it becomes critical when surface and subsurface become more tightly coupled with groundwater table within 6 to 7 meters below the surface. Inclusion of lateral subsurface flow influenced both the surface energy budget and subsurface transport processes as a result of river-water intrusion into the subsurface in response to an elevated river stage that increased soil moisture for evapotranspiration and suppressed available energy for sensible heat in the warm season. The coupled model developed in this study can be used for improving mechanistic understanding of ecosystem functioning and biogeochemical cycling along river corridors under historical and future hydroclimatic changes. The dataset presented in this study can also serve as a good benchmarking case for testing other integrated models.« less

Using Bacterial Surrogates to Assess Pathogen Transport in the Subsurface: Laboratory and Field Indications of Co-Transport Considerations

NASA Astrophysics Data System (ADS)

Emelko, M.; Stimson, J. R.; McLellan, N. L.; Mesquita, M.

2009-12-01

Prediction of the transport and fate of colloids and nanoparticles in porous media environments remains challenging because factors such as experimental scale, subsurface heterogeneity, and variable flow paths and fluxes have made it difficult to relate laboratory outcomes to field performance. Moreover, field studies have been plagued with inadequate consideration of ground water flow, reliance on unproven “surrogate” parameters, non-detects at the extraction well, and limited sampling. Riverbank filtration (RBF) is an example of an application for which some predictive capacity regarding colloid transport is desirable. RBF is a relatively low-cost, natural water treatment technology in which surface water contaminants are removed or degraded as the infiltrating water flows from a surface source to abstraction wells. RBF has been used for water treatment for at least 200 years and its potential to provide a significant barrier to microorganisms has been demonstrated. Assignment of microbial treatment credits for RBF remains a regulatory challenge because strategies for demonstrating effective subsurface filtration of organisms are not standardized. The potential passage of Giardia lamblia and Cryptosporidium parvum through RBF systems is of particular regulatory concern because these pathogens are known to be resistant to conventional disinfection processes. The transport or relatively small, pathogenic viruses through RBF systems is also a common concern. To comply with the U.S. Long Term 2 Enhanced Surface Water Treatment Rule, utilities with sufficiently high levels of Cryptosporidium oocysts in their source water must amend existing treatment by choosing from a ‘‘toolbox’’ of technologies, including RBF. Aerobic bacterial spores have been evaluated and proposed by some as surrogates for evaluating drinking water treatment plant performance; they also have been proposed as potential surrogates for Cryptosporidium removal during subsurface filtration processes such as RBF. Here, duplicate column studies were conducted to evaluate the transport of nano- and micro-sized polystyrene micropsheres, aerobic spores of Bacillus subtilis, PR772 bacteriophage, and pathogenic Salmonella typhimurium bacteria in a well-sorted fine sand (d 50 = 0.6 mm). A field validation experiment investigating transport of 1.5 µm polystyrene micropsheres and aerobic spores in and RBF system comprised of unconsolidated silty sand, gravel, and boulders was conducted. The column studies demonstrated that the presence of the aerobic spores resulted in increased removal of 4.5 µm microspheres from< 2 log to ~4 log, and 1.5 µm microsphere removal from <0.5 log to ~1 log removal. Microscopic examination of the samples also revealed extensive clumping of microspheres and microorganisms during the experiments conducted with aerobic spores. A field trial during which microspheres and spores of B. subtilis were injected into the subsurface provided corroborating evidence of a co-transport effect of aerobic spores by demonstrating ~1.6 log increase in 1.5 µm microsphere removal in the presence of aerobic spores.

Effect of Selected Modeling Assumptions on Subsurface Radionuclide Transport Projections for the Potential Environmental Management Disposal Facility at Oak Ridge, Tennessee

DOE Office of Scientific and Technical Information (OSTI.GOV)

Painter, Scott L.

2016-06-28

The Department of Energy’s Office of Environmental Management recently revised a Remedial Investigation/ Feasibility Study (RI/FS) that included an analysis of subsurface radionuclide transport at a potential new Environmental Management Disposal Facility (EMDF) in East Bear Creek Valley near Oak Ridge, Tennessee. The effect of three simplifying assumptions used in the RI/FS analyses are investigated using the same subsurface pathway conceptualization but with more flexible modeling tools. Neglect of vadose zone dispersion was found to be conservative or non-conservative, depending on the retarded travel time and the half-life. For a given equilibrium distribution coefficient, a relatively narrow range of half-lifemore » was identified for which neglect of vadose zone transport is non-conservative and radionuclide discharge into surface water is non-negligible. However, there are two additional conservative simplifications in the reference case that compensate for the non-conservative effect of neglecting vadose zone dispersion: the use of a steady infiltration rate and vadose zone velocity, and the way equilibrium sorption is used to represent transport in the fractured material of the saturated aquifer. With more realistic representations of all three processes, the RI/FS reference case was found to either provide a reasonably good approximation to the peak concentration or was significantly conservative (pessimistic) for all parameter combinations considered.« less

Lattice Boltzmann-Based Approaches for Pore-Scale Reactive Transport

DOE PAGES

Yoon, Hongkyu; Kang, Qinjun; Valocchi, Albert J.

2015-07-29

Here an important geoscience and environmental applications such as geologic carbon storage, environmental remediation, and unconventional oil and gas recovery are best understood in the context of reactive flow and multicomponent transport in the subsurface environment. The coupling of chemical and microbiological reactions with hydrological and mechanical processes can lead to complex behaviors across an enormous range of spatial and temporal scales. These coupled responses are also strongly influenced by the heterogeneity and anisotropy of the geologic formations. Reactive transport processes can change the pore morphology at the pore scale, thereby leading to nonlinear interactions with advective and diffusive transport,more » which can strongly influence larger-scale properties such as permeability and dispersion.« less

Influence Of pH On The Transport Of Nanoscale Zinc Oxide In Saturated Porous Media

EPA Science Inventory

Widespread use of nanoscale zinc oxide (nZnO) in various fields causes subsurface environment contamination. Even though the transport of dissolved zinc ions in subsurface environments such as soils and sediments has been widely studied, the transport mechanism of nZnO in such e...

Three-Dimensional Subsurface Flow, Fate and Transport of Microbes and Chemicals (3DFATMIC) Model

EPA Pesticide Factsheets

This model simulates subsurface flow, fate and transport of contaminants that are undergoing chemical or biological transformations. The model is applicable to transient conditions in both saturated and unsaturated zones.

Two-Dimensional Subsurface Flow, Fate and Transport of Microbes and Chemicals (2DFATMIC) Model

EPA Pesticide Factsheets

This model simulates subsurface flow, fate, and transport of contaminants that are undergoing chemical or biological transformations. This model is applicable to transient conditions in both saturated and unsaturated zones.

Impacts of microtopographic snow-redistribution and lateral subsurface processeson hydrologic and thermal states in an Arctic polygonal ground ecosystem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bisht, Gautam; Riley, William J.; Wainwright, Haruko M.

Microtopographic features, such as polygonal ground, are characteristic sources of landscape heterogeneity in the Alaskan Arctic coastal plain. We analyze the effects of snow redistribution (SR) and lateral subsurface processes on hydrologic and thermal states at a polygonal tundra site near Barrow, Alaska. We extended the land model integrated in the ACME Earth System Model (ESM) to redistribute incoming snow by accounting for microtopography and incorporated subsurface lateral transport of water and energy (ALMv0-3D). Three 10-years long simulations were performed for a transect across polygonal tundra landscape at the Barrow Environmental Observatory in Alaska to isolate the impact of SRmore » and subsurface process representation. When SR was included, model results show a better agreement (higher R 2 with lower bias and RMSE) for the observed differences in snow depth between polygonal rims and centers. The model was also able to accurately reproduce observed soil temperature vertical profiles in the polygon rims and centers (overall bias, RMSE, and R 2 of 0.59°C, 1.82°C, and 0.99, respectively). The spatial heterogeneity of snow depth during the winter due to SR generated surface soil temperature heterogeneity that propagated in depth and time and led to ~10 cm shallower and ~5 cm deeper maximum annual thaw depths under the polygon rims and centers, respectively. Additionally, SR led to spatial heterogeneity in surface energy fluxes and soil moisture during the summer. Excluding lateral subsurface hydrologic and thermal processes led to small effects on mean states but an overestimation of spatial variability in soil moisture and soil temperature as subsurface liquid pressure and thermal gradients were artificially prevented from spatially dissipating over time. The effect of lateral subsurface processes on active layer depths was modest with mean absolute difference of ~3 cm. Finally, our integration of three-dimensional subsurface hydrologic and thermal subsurface dynamics in the ACME land model will facilitate a wide range of analyses heretofore impossible in an ESM context.« less

Impacts of microtopographic snow-redistribution and lateral subsurface processeson hydrologic and thermal states in an Arctic polygonal ground ecosystem

DOE PAGES

Bisht, Gautam; Riley, William J.; Wainwright, Haruko M.; ...

2018-01-08

Microtopographic features, such as polygonal ground, are characteristic sources of landscape heterogeneity in the Alaskan Arctic coastal plain. We analyze the effects of snow redistribution (SR) and lateral subsurface processes on hydrologic and thermal states at a polygonal tundra site near Barrow, Alaska. We extended the land model integrated in the ACME Earth System Model (ESM) to redistribute incoming snow by accounting for microtopography and incorporated subsurface lateral transport of water and energy (ALMv0-3D). Three 10-years long simulations were performed for a transect across polygonal tundra landscape at the Barrow Environmental Observatory in Alaska to isolate the impact of SRmore » and subsurface process representation. When SR was included, model results show a better agreement (higher R 2 with lower bias and RMSE) for the observed differences in snow depth between polygonal rims and centers. The model was also able to accurately reproduce observed soil temperature vertical profiles in the polygon rims and centers (overall bias, RMSE, and R 2 of 0.59°C, 1.82°C, and 0.99, respectively). The spatial heterogeneity of snow depth during the winter due to SR generated surface soil temperature heterogeneity that propagated in depth and time and led to ~10 cm shallower and ~5 cm deeper maximum annual thaw depths under the polygon rims and centers, respectively. Additionally, SR led to spatial heterogeneity in surface energy fluxes and soil moisture during the summer. Excluding lateral subsurface hydrologic and thermal processes led to small effects on mean states but an overestimation of spatial variability in soil moisture and soil temperature as subsurface liquid pressure and thermal gradients were artificially prevented from spatially dissipating over time. The effect of lateral subsurface processes on active layer depths was modest with mean absolute difference of ~3 cm. Finally, our integration of three-dimensional subsurface hydrologic and thermal subsurface dynamics in the ACME land model will facilitate a wide range of analyses heretofore impossible in an ESM context.« less

On the effects of subsurface parameters on evaporite dissolution (Switzerland)

NASA Astrophysics Data System (ADS)

Zidane, Ali; Zechner, Eric; Huggenberger, Peter; Younes, Anis

2014-05-01

Uncontrolled subsurface evaporite dissolution could lead to hazards such as land subsidence. Observed subsidences in a study area of Northwestern Switzerland were mainly due to subsurface dissolution (subrosion) of evaporites such as halite and gypsum. A set of 2D density driven flow simulations were evaluated along 1000 m long and 150 m deep 2D cross sections within the study area that is characterized by tectonic horst and graben structures. The simulations were conducted to study the effect of the different subsurface parameters that could affect the dissolution process. The heterogeneity of normal faults and its impact on the dissolution of evaporites is studied by considering several permeable faults that include non-permeable areas. The mixed finite element method (MFE) is used to solve the flow equation, coupled with the multipoint flux approximation (MPFA) and the discontinuous Galerkin method (DG) to solve the diffusion and the advection parts of the transport equation.

Murt user`s guide: A hybrid Lagrangian-Eulerian finite element model of multiple-pore-region solute transport through subsurface media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gwo, J.P.; Jardine, P.M.; Yeh, G.T.

Matrix diffusion, a diffusive mass transfer process,in the structured soils and geologic units at ORNL, is believe to be an important subsurface mass transfer mechanism; it may affect off-site movement of radioactive wastes and remediation of waste disposal sites by locally exchanging wastes between soil/rock matrix and macropores/fractures. Advective mass transfer also contributes to waste movement but is largely neglected by researchers. This report presents the first documented 2-D multiregion solute transport code (MURT) that incorporates not only diffusive but also advective mass transfer and can be applied to heterogeneous porous media under transient flow conditions. In this report, theoreticalmore » background is reviewed and the derivation of multiregion solute transport equations is presented. Similar to MURF (Gwo et al. 1994), a multiregion subsurface flow code, multiplepore domains as suggested by previous investigators (eg, Wilson and Luxmoore 1988) can be implemented in MURT. Transient or steady-state flow fields of the pore domains can be either calculated by MURF or by modelers. The mass transfer process is briefly discussed through a three-pore-region multiregion solute transport mechanism. Mass transfer equations that describe mass flux across pore region interfaces are also presented and parameters needed to calculate mass transfer coefficients detailed. Three applications of MURT (tracer injection problem, sensitivity analysis of advective and diffusive mass transfer, hillslope ponding infiltration and secondary source problem) were simulated and results discussed. Program structure of MURT and functions of MURT subroutiness are discussed so that users can adapt the code; guides for input data preparation are provided in appendices.« less

Final Technical Report: Viral Infection of Subsurface Microorganisms and Metal/Radionuclide Transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weber, Karrie A.; Bender, Kelly S.; Li, Yusong

Microbially mediated metabolisms have been identified as a significant factor either directly or indirectly impacting the fate and transport of heavy metal/radionuclide contaminants. To date microorganisms have been isolated from contaminated environments. Examination of annotated finished genome sequences of many of these subsurface isolates from DOE sites, revealed evidence of prior viral infection. To date the role that viruses play influencing microbial mortality and the resulting community structure which directly influences biogeochemical cycling in soils and sedimentary environments remains poorly understood. The objective of this exploratory study was to investigate the role of viral infection of subsurface bacteria and themore » formation of contaminant-bearing viral particles. This objective was approached by examining the following working hypotheses: (i) subsurface microorganisms are susceptible to viral infections by the indigenous subsurface viral community, and (ii) viral surfaces will adsorb heavy metals and radionuclides. Our results have addressed basic research needed to accomplish the BER Long Term Measure to provide sufficient scientific understanding such that DOE sites would be able to incorporate coupled physical, chemical and biological processes into decision making for environmental remediation or natural attenuation and long-term stewardship by establishing viral-microbial relationships on the subsequent fate and transport of heavy metals and radionuclides. Here we demonstrated that viruses play a significant role in microbial mortality and community structure in terrestrial subsurface sedimentary systems. The production of viral-like particles within subsurface sediments in response to biostimulation with dissolved organic carbon and a terminal electron acceptor resulted in the production of viral-like particles. Organic carbon alone did not result in significant viral production and required the addition of a terminal electron acceptor (nitrate), indicating that nutrients are not limiting viral production, but rather substrates that can be converted into energy for host metabolism. Our results also revealed that cell abundance was not correlated to the mineralization of organic carbon, but rather viruses were positively correlated with carbon mineralization. This is a result of viral-mediated cell lysis and demonstrates that viruses are sensitive indicators of microbial activity. Viruses as an indicator of microbial activity was not unique to batch culture studies as results obtained from an in situ field experiment conducted at the DOE Old Rifle Field site. This study revealed that viral abundance increased in response to the injection of oxygenated groundwater and influx of dissolved organic carbon whereas cell abundance changes were minimal. However, the extent to which viral-mediated cell lysis alters organic matter pools subsequently influencing microbial community structure and biogeochemical function remains a critical question in subsurface biogeochemical cycling. The production of significant numbers of viruses in groundwater has implications for nanoparticulate metal as well as carbon transport in groundwater. We have demonstrated that the virus surface is reactive and will adsorb heavy metals. Thus viruses can promote colloidal contaminant mobility. Interestingly, the presence of heavy metals has a positive effect on infectivity of the phage, increasing phage infection which could lead to further production of viruses. Together, the results indicate that the sorption of metals to the surface of viruses could not only contribute to nanoparticulate metal as well as carbon transport but could also enhance infectivity further contributing to cell lysis which could subsequently influence biogeochemical cycling. As more viruses infect host microbial populations the high concentration of metals would enhance infection, resulting in cell lysis, and decreasing the metabolically active host population while yielding greater numbers of viruses capable of transporting contaminats. Additional studies will be necessary to further establish the potential relationship(s) between viruses, cells, carbon, and metals/radionuclides to provide sufficient scientific understanding to incorporate coupled physical, chemical, and biological processes into agent based and reactive transport models.« less

Impact of Subsurface Heterogeneities on nano-Scale Zero Valent Iron Transport

NASA Astrophysics Data System (ADS)

Krol, M. M.; Sleep, B. E.; O'Carroll, D. M.

2011-12-01

Nano-scale zero valent iron (nZVI) has been applied as a remediation technology at sites contaminated with chlorinated compounds and heavy metals. Although laboratory studies have demonstrated high reactivity for the degradation of target contaminants, the success of nZVI in the field has been limited due to poor subsurface mobility. When injected into the subsurface, nZVI tends to aggregate and be retained by subsurface soils. As such nZVI suspensions need to be stabilized for increased mobility. However, even with stabilization, soil heterogeneities can still lead to non-uniform nZVI transport, resulting in poor distribution and consequently decreased degradation of target compounds. Understanding how nZVI transport can be affected by subsurface heterogeneities can aid in improving the technology. This can be done with the use of a numerical model which can simulate nZVI transport. In this study CompSim, a finite difference groundwater model, is used to simulate the movement of nZVI in a two-dimensional domain. CompSim has been shown in previous studies to accurately predict nZVI movement in the subsurface, and is used in this study to examine the impact of soil heterogeneity on nZVI transport. This work also explores the impact of different viscosities of the injected nZVI suspensions (corresponding to different stabilizing polymers) and injection rates on nZVI mobility. Analysis metrics include travel time, travel distance, and average nZVI concentrations. Improving our understanding of the influence of soil heterogeneity on nZVI transport will lead to improved field scale implementation and, potentially, to more effective remediation of contaminated sites.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aleman, S.E.

This report documents a finite element code designed to model subsurface flow and contaminant transport, named FACT. FACT is a transient three-dimensional, finite element code designed to simulate isothermal groundwater flow, moisture movement, and solute transport in variably saturated and fully saturated subsurface porous media.

Applying model abstraction techniques to optimize monitoring networks for detecting subsurface contaminant transport

USDA-ARS?s Scientific Manuscript database

Improving strategies for monitoring subsurface contaminant transport includes performance comparison of competing models, developed independently or obtained via model abstraction. Model comparison and parameter discrimination involve specific performance indicators selected to better understand s...

Contaminated environments in the subsurface and bioremediation: organic contaminants.

PubMed

Holliger, C; Gaspard, S; Glod, G; Heijman, C; Schumacher, W; Schwarzenbach, R P; Vazquez, F

1997-07-01

Due to leakages, spills, improper disposal and accidents during transport, organic compounds have become subsurface contaminants that threaten important drinking water resources. One strategy to remediate such polluted subsurface environments is to make use of the degradative capacity of bacteria. It is often sufficient to supply the subsurface with nutrients such as nitrogen and phosphorus, and aerobic treatments are still dominating. However, anaerobic processes have advantages such as low biomass production and good electron acceptor availability, and they are sometimes the only possible solution. This review will focus on three important groups of environmental organic contaminants: hydrocarbons, chlorinated and nitroaromatic compounds. Whereas hydrocarbons are oxidized and completely mineralized under anaerobic conditions in the presence of electron acceptors such as nitrate, iron, sulfate and carbon dioxide, chlorinated and nitroaromatic compounds are reductively transformed. For the aerobic often persistent polychlorinated compounds, reductive dechlorination leads to harmless products or to compounds that are aerobically degradable. The nitroaromatic compounds are first reductively transformed to the corresponding amines and can subsequently be bound to the humic fraction in an aerobic process. Such new findings and developments give hope that in the near future contaminated aquifers can efficiently be remediated, a prerequisite for a sustainable use of the precious-subsurface drinking water resources.

Reactive transport codes for subsurface environmental simulation

DOE PAGES

Steefel, C. I.; Appelo, C. A. J.; Arora, B.; ...

2014-09-26

A general description of the mathematical and numerical formulations used in modern numerical reactive transport codes relevant for subsurface environmental simulations is presented. The formulations are followed by short descriptions of commonly used and available subsurface simulators that consider continuum representations of flow, transport, and reactions in porous media. These formulations are applicable to most of the subsurface environmental benchmark problems included in this special issue. The list of codes described briefly here includes PHREEQC, HPx, PHT3D, OpenGeoSys (OGS), HYTEC, ORCHESTRA, TOUGHREACT, eSTOMP, HYDROGEOCHEM, CrunchFlow, MIN3P, and PFLOTRAN. The descriptions include a high-level list of capabilities for each of themore » codes, along with a selective list of applications that highlight their capabilities and historical development.« less

Hyporheic transport in headwater mountain streams is time-invariant in locations where geologic controls dominate hydrologic forcin

NASA Astrophysics Data System (ADS)

Ward, A. S.; Schmadel, N.; Wondzell, S. M.; Harman, C. J.; Gooseff, M. N.; Singha, K.

2015-12-01

Transport along riparian and hyporheic flowpaths is generally believed to integrate the responses of streams and aquifers to dynamic hydrological forcing. Although it is generally expected transport along these flow paths is time-variable, such dynamic responses have seldom been demonstrated. Further, we do not understand how hydrological forcing interacts with local geologic setting (i.e., valley and streambed morphology) We conducted a series of four stream solute tracer injections in each of two watersheds with contrasting valley morphology in the H.J. Andrews Experimental Forest, monitoring tracer concentrations in the stream and in a network of shallow wells in each watershed. Time series analyses were used to deconvolve transport along subsurface flowpaths from transport in the stream channel. We found time-invariant hyporheic transport in the narrow, bedrock-constrained valley and near large roughness elements (e.g., steps, logs) in the wider valley bottom despite order of magnitude changes in discharge, suggesting geologic controls dominate hyporheic transport in these locations. In contrast, we observed increases in mean arrival time and temporal variance with decreasing discharge at the riparian-hillslope transition, suggesting hydrological dynamics control transport in these locations. We pose several mechanisms by which dynamic hydrology and geologic setting interact that may explain the observed behavior. We interpret time-invariant transport as an indication that discharge in the surface stream is a poor predictor of exchange along the stream-hyporheic-riparian-hillslope continuum in headwater valleys. As such, models able to account for the transition from geologically-dominated processes in the near-stream subsurface to hydrologically-dominated processes near the hillslope are required to predict transport and fate in valley bottoms of headwater mountain streams.

VIRUS TRANSPORT IN PHYSICALLY AND GEOCHEMICALLY HETEROGENEOUS SUBSURFACE POROUS MEDIA. (R826179)

EPA Science Inventory

A two-dimensional model for virus transport in physically and geochemically heterogeneous subsurface porous media is presented. The model involves solution of the advection–dispersion equation, which additionally considers virus inactivation in the solution, as well as ...

Integrating surrogate models into subsurface simulation framework allows computation of complex reactive transport scenarios

NASA Astrophysics Data System (ADS)

De Lucia, Marco; Kempka, Thomas; Jatnieks, Janis; Kühn, Michael

2017-04-01

Reactive transport simulations - where geochemical reactions are coupled with hydrodynamic transport of reactants - are extremely time consuming and suffer from significant numerical issues. Given the high uncertainties inherently associated with the geochemical models, which also constitute the major computational bottleneck, such requirements may seem inappropriate and probably constitute the main limitation for their wide application. A promising way to ease and speed-up such coupled simulations is achievable employing statistical surrogates instead of "full-physics" geochemical models [1]. Data-driven surrogates are reduced models obtained on a set of pre-calculated "full physics" simulations, capturing their principal features while being extremely fast to compute. Model reduction of course comes at price of a precision loss; however, this appears justified in presence of large uncertainties regarding the parametrization of geochemical processes. This contribution illustrates the integration of surrogates into the flexible simulation framework currently being developed by the authors' research group [2]. The high level language of choice for obtaining and dealing with surrogate models is R, which profits from state-of-the-art methods for statistical analysis of large simulations ensembles. A stand-alone advective mass transport module was furthermore developed in order to add such capability to any multiphase finite volume hydrodynamic simulator within the simulation framework. We present 2D and 3D case studies benchmarking the performance of surrogates and "full physics" chemistry in scenarios pertaining the assessment of geological subsurface utilization. [1] Jatnieks, J., De Lucia, M., Dransch, D., Sips, M.: "Data-driven surrogate model approach for improving the performance of reactive transport simulations.", Energy Procedia 97, 2016, p. 447-453. [2] Kempka, T., Nakaten, B., De Lucia, M., Nakaten, N., Otto, C., Pohl, M., Chabab [Tillner], E., Kühn, M.: "Flexible Simulation Framework to Couple Processes in Complex 3D Models for Subsurface Utilization Assessment.", Energy Procedia, 97, 2016 p. 494-501.

Effects of Surface and Subsurface Bed Material Composition on Gravel Transport and Flow Competence Relations—Possibilities for Prediction

NASA Astrophysics Data System (ADS)

Bunte, K.; Abt, S. R.; Swingle, K. W.; Cenderelli, D. A.; Gaeuman, D. A.

2014-12-01

Bedload transport and flow competence relations are difficult to predict in coarse-bedded steep streams where widely differing sediment supply, bed stability, and complex flow hydraulics greatly affect amounts and sizes of transported gravel particles. This study explains how properties of bed material surface and subsurface size distributions are directly related to gravel transport and may be used for prediction of gravel transport and flow competence relations. Gravel transport, flow competence, and bed material size were measured in step-pool and plane-bed streams. Power functions were fitted to gravel transport QB=aQb and flow competence Dmax=cQd relations; Q is water discharge. Frequency distributions of surface FDsurf and subsurface FDsub bed material were likewise described by power functions FDsurf=hD j and FDsub=kDm fitted over six 0.5-phi size classes within 4 to 22.4 mm. Those gravel sizes are typically mobile even in moderate floods. Study results show that steeper subsurface bed material size distributions lead to steeper gravel transport and flow competence relations, whereas larger amounts of sediment contained in those 6 size bedmaterial classes (larger h and k) flatten the relations. Similarly, steeper surface size distributions decrease the coefficients of the gravel transport and flow competence relations, whereas larger amounts of sediment within the six bed material classes increase the intercepts of gravel transport and flow competence relations. Those relations are likely causative in streams where bedload stems almost entirely from the channel bed as opposed to direct (unworked) contributions from hillslopes and tributaries. The exponent of the subsurface bed material distribution m predicted the gravel transport exponent b with r2 near 0.7 and flow competence exponent d with r2 near 0.5. The intercept of bed surface distributions h increased the intercept a of gravel transport and c of the flow competence relations with r2 near 0.6.

An open, object-based modeling approach for simulating subsurface heterogeneity

NASA Astrophysics Data System (ADS)

Bennett, J.; Ross, M.; Haslauer, C. P.; Cirpka, O. A.

2017-12-01

Characterization of subsurface heterogeneity with respect to hydraulic and geochemical properties is critical in hydrogeology as their spatial distribution controls groundwater flow and solute transport. Many approaches of characterizing subsurface heterogeneity do not account for well-established geological concepts about the deposition of the aquifer materials; those that do (i.e. process-based methods) often require forcing parameters that are difficult to derive from site observations. We have developed a new method for simulating subsurface heterogeneity that honors concepts of sequence stratigraphy, resolves fine-scale heterogeneity and anisotropy of distributed parameters, and resembles observed sedimentary deposits. The method implements a multi-scale hierarchical facies modeling framework based on architectural element analysis, with larger features composed of smaller sub-units. The Hydrogeological Virtual Reality simulator (HYVR) simulates distributed parameter models using an object-based approach. Input parameters are derived from observations of stratigraphic morphology in sequence type-sections. Simulation outputs can be used for generic simulations of groundwater flow and solute transport, and for the generation of three-dimensional training images needed in applications of multiple-point geostatistics. The HYVR algorithm is flexible and easy to customize. The algorithm was written in the open-source programming language Python, and is intended to form a code base for hydrogeological researchers, as well as a platform that can be further developed to suit investigators' individual needs. This presentation will encompass the conceptual background and computational methods of the HYVR algorithm, the derivation of input parameters from site characterization, and the results of groundwater flow and solute transport simulations in different depositional settings.

3DFATMIC: THREE DIMENSIONAL SUBSURFACE FLOW, FATE AND TRANSPORT OF MICROBES AND CHEMICALS MODEL - USER'S MANUAL VERSION 1.0

EPA Science Inventory

This document is the user's manual of 3DFATMIC, a 3-Dimensional Subsurface Flow, Fate and Transport of Microbes and Chemicals Model using a Lagrangian-Eulerian adapted zooming and peak capturing (LEZOOMPC) algorithm.

Evaluation of the hydrological flow paths in a gravel bed filter modeling a horizontal subsurface flow wetland by using a multi-tracer experiment.

PubMed

Birkigt, Jan; Stumpp, Christine; Małoszewski, Piotr; Nijenhuis, Ivonne

2018-04-15

In recent years, constructed wetland systems have become into focus as means of cost-efficient organic contaminant management. Wetland systems provide a highly reactive environment in which several removal pathways of organic chemicals may be present at the same time; however, specific elimination processes and hydraulic conditions are usually separately investigated and thus not fully understood. The flow system in a three dimensional pilot-scale horizontal subsurface constructed wetland was investigated applying a multi-tracer test combined with a mathematical model to evaluate the flow and transport processes. The results indicate the existence of a multiple flow system with two distinct flow paths through the gravel bed and a preferential flow at the bottom transporting 68% of tracer mass resulting from the inflow design of the model wetland system. There the removal of main contaminant chlorobenzene was up to 52% based on different calculation approaches. Determined retention times in the range of 22d to 32.5d the wetland has a heterogeneous flow pattern. Differences between simulated and measured tracer concentrations in the upper sediment indicate diffusion dominated processes due to stagnant water zones. The tracer study combining experimental evaluation with mathematical modeling demonstrated the complexity of flow and transport processes in the constructed wetlands which need to be taken into account during interpretation of the determining attenuation processes. Copyright © 2017 Elsevier B.V. All rights reserved.

Effects of Atmospheric Conditions and the Land/Atmospheric Interface on Transport of Chemical Vapors from Subsurface Sources

NASA Astrophysics Data System (ADS)

Rice, A. K.; Smits, K. M.; Cihan, A.; Howington, S. E.; Illangasekare, T. H.

2013-12-01

Understanding the movement of chemical vapors and gas through variably saturated soil subjected to atmospheric thermal and mass flux boundary conditions at the land/atmospheric interface is important to many applications, including landmine detection, methane leakage during natural gas production from shale and CO2 leakage from deep geologic storage. New, advanced technologies exist to sense chemical signatures and gas leakage at the land/atmosphere interface, but interpretation of sensor signals remains a challenge. Chemical vapors are subject to numerous interactions while migrating through the soil environment, masking source conditions. The process governing movement of gases through porous media is often assumed to be Fickian diffusion through the air phase with minimal quantification of other processes, such as convective gas flow and temporal or spatial variation in soil moisture. Vapor migration is affected by atmospheric conditions (e.g. humidity, temperature, wind velocity), soil thermal and hydraulic properties and contaminant properties, all of which are physically and thermodynamically coupled. The complex coupling of two drastically different flow regimes in the subsurface and atmosphere is commonly ignored in modeling efforts, or simplifying assumptions are made to treat the systems as de-coupled. Experimental data under controlled laboratory settings are lacking to refine the theory for proper coupling and complex treatment of vapor migration through porous media in conversation with atmospheric flow and climate variations. Improving fundamental understanding and accurate quantification of these processes is not feasible in field settings due to lack of controlled initial and boundary conditions and inability to fully characterize the subsurface at all relevant scales. The goal of this work is to understand the influence of changes in atmospheric conditions to transport of vapors through variably saturated soil. We have developed a tank apparatus with a network of soil and atmospheric sensors and a head space for air flow to simulate the atmospheric boundary layer. Experiments were performed under varying temperature values at the soil surface bounded by the atmospheric boundary layer. The model of Smits et al. [2011], accounting for non-equilibrium phase change and coupled heat, water vapor and liquid water flux through soil, was amended to include organic vapor in the gas phase and migration mechanisms often overlooked in models (thermal and Knudsen diffusion, density driven advection). Experimental results show increased vapor mass flux across the soil/atmospheric interface due to heat applied from the atmosphere and coupling of heat and mass transfer in the shallow subsurface for both steady and diurnal temperature patterns. Comparison of model results to experimental data shows dynamic interactions between transport in porous media and boundary conditions. Results demonstrate the value of considering interactions of the atmosphere and subsurface to better understand chemical gas transport through unsaturated soils and the land/atmospheric interface.

3D numerical modeling of hyporheic exchange processes in fractal riverbed

NASA Astrophysics Data System (ADS)

Lee, A.; Aubeneau, A.

2017-12-01

The subsurface region receiving stream water is known as the hyporheic zone and the flow of water in and out of this zone is called hyporheic exchange. The hyporheic zone is populated by biofilms and is a hotspot for nutrient uptake and contaminant transformation. Traditionally, pumping models predicting the head distribution over the riverbed boundary are used to obtain the velocity field in the subsurface. However, past research has largely overlooked the nonlinearity of the turbulent flow above the bumpy riverbed. The main objective of this research is to investigate the effect of spatial and temporal heterogeneity created by turbulent flow on hyporheic exchange and residence time distribution in fractal channel beds. The 3-D fractal riverbed is created from the power spectrum. Large-Eddy Simulation is used to provide the pressure field over the benthic boundary. Finally, Darcian fluxes in the sub-surface are calculated and hyporheic travel times computed using random walks. Surface and subsurface transport processes are represented explicitly and can be studied in detail. Our results suggest that (1) Eddies and wakes around the dunes force the exchange (2) The bigger the dunes, the greater the influence of turbulence (3) Turbulence induces more exchange than pumping predicts.

Escherichia coli Transport from Surface-Applied Manure to Subsurface Drains through Artificial Biopores

USDA-ARS?s Scientific Manuscript database

Transport of pathogenic bacteria in soils primarily occurs through soil mesopores and macropores (e.g., biopores and cracks). Field research has demonstrated that biopores and subsurface drains can be hydraulically connected. This research was conducted to investigate the importance of surface conne...

Modeling Aspect Controlled Formation of Seasonally Frozen Ground on Montane Hillslopes: a Case Study from Gordon Gulch, Colorado

NASA Astrophysics Data System (ADS)

Rush, M.; Rajaram, H.; Anderson, R. S.; Anderson, S. P.

2017-12-01

The Intergovernmental Panel on Climate Change (2013) warns that high-elevation ecosystems are extremely vulnerable to climate change due to short growing seasons, thin soils, sparse vegetation, melting glaciers, and thawing permafrost. Many permafrost-free regions experience seasonally frozen ground. The spatial distribution of frozen soil exerts a strong control on subsurface flow and transport processes by reducing soil permeability and impeding infiltration. Accordingly, evolution of the extent and duration of frozen ground may alter streamflow seasonality, groundwater flow paths, and subsurface storage, presenting a need for coupled thermal-hydrologic models to project hydrologic responses to climate warming in high-elevation regions. To be useful as predictive tools, such models should incorporate the heterogeneity of solar insolation, vegetation, and snowpack dynamics. We present a coupled thermal-hydrologic modeling study against the backdrop of field observations from Gordon Gulch, a seasonally snow-covered montane catchment in the Colorado Front Range in the Boulder Creek Critical Zone Observatory. The field site features two instrumented hillslopes with opposing aspects: the snowpack on the north-facing slope persists throughout much of the winter season, while the snowpack on the south-facing slope is highly ephemeral. We implemented a surface energy balance and snowpack accumulation and ablation model that is coupled to the subsurface flow and transport code PFLOTRAN-ICE to predict the hydrologic consequences of aspect-controlled frozen soil formation during water years 2013-2016. Preliminary model results demonstrate the occurrence of seasonally-frozen ground on the north-facing slope that directs snowmelt to the stream by way of shallow subsurface flow paths. The absence of persistently frozen ground on the south-facing slope allows deeper infiltration of snowmelt recharge. The differences in subsurface flow paths also suggest strong aspect-controlled heterogeneities in nitrate export and differences in geomorphic processes such as frost creep.

Reactive Transport Modeling of Induced Calcite Precipitation Reaction Fronts in Porous Media Using A Parallel, Fully Coupled, Fully Implicit Approach

NASA Astrophysics Data System (ADS)

Guo, L.; Huang, H.; Gaston, D.; Redden, G. D.; Fox, D. T.; Fujita, Y.

2010-12-01

Inducing mineral precipitation in the subsurface is one potential strategy for immobilizing trace metal and radionuclide contaminants. Generating mineral precipitates in situ can be achieved by manipulating chemical conditions, typically through injection or in situ generation of reactants. How these reactants transport, mix and react within the medium controls the spatial distribution and composition of the resulting mineral phases. Multiple processes, including fluid flow, dispersive/diffusive transport of reactants, biogeochemical reactions and changes in porosity-permeability, are tightly coupled over a number of scales. Numerical modeling can be used to investigate the nonlinear coupling effects of these processes which are quite challenging to explore experimentally. Many subsurface reactive transport simulators employ a de-coupled or operator-splitting approach where transport equations and batch chemistry reactions are solved sequentially. However, such an approach has limited applicability for biogeochemical systems with fast kinetics and strong coupling between chemical reactions and medium properties. A massively parallel, fully coupled, fully implicit Reactive Transport simulator (referred to as “RAT”) based on a parallel multi-physics object-oriented simulation framework (MOOSE) has been developed at the Idaho National Laboratory. Within this simulator, systems of transport and reaction equations can be solved simultaneously in a fully coupled, fully implicit manner using the Jacobian Free Newton-Krylov (JFNK) method with additional advanced computing capabilities such as (1) physics-based preconditioning for solution convergence acceleration, (2) massively parallel computing and scalability, and (3) adaptive mesh refinements for 2D and 3D structured and unstructured mesh. The simulator was first tested against analytical solutions, then applied to simulating induced calcium carbonate mineral precipitation in 1D columns and 2D flow cells as analogs to homogeneous and heterogeneous porous media, respectively. In 1D columns, calcium carbonate mineral precipitation was driven by urea hydrolysis catalyzed by urease enzyme, and in 2D flow cells, calcium carbonate mineral forming reactants were injected sequentially, forming migrating reaction fronts that are typically highly nonuniform. The RAT simulation results for the spatial and temporal distributions of precipitates, reaction rates and major species in the system, and also for changes in porosity and permeability, were compared to both laboratory experimental data and computational results obtained using other reactive transport simulators. The comparisons demonstrate the ability of RAT to simulate complex nonlinear systems and the advantages of fully coupled approaches, over de-coupled methods, for accurate simulation of complex, dynamic processes such as engineered mineral precipitation in subsurface environments.

Evaluating Potential Exposures to Ecological Receptors Due to Transport of Hydrophobic Organic Contaminants in Subsurface Systems (Final Report)

EPA Science Inventory

EPA's Ecological Risk Assessment Support Center (ERASC) announced the release of the final report, Evaluating Potential Exposures to Ecological Receptors Due to Transport of Hydrophobic Organic Contaminants in Subsurface Systems. This technical paper recommends several ty...

3DHYDROGEOCHEM: A 3-DIMENSIONAL MODEL OF DENSITY-DEPENDENT SUBSURFACE FLOW AND THERMAL MULTISPECIES-MULTICOMPONENT HYDROGEOCHEMICAL TRANSPORT

EPA Science Inventory

This report presents a three-dimensional finite-element numerical model designed to simulate chemical transport in subsurface systems with temperature effect taken into account. The three-dimensional model is developed to provide (1) a tool of application, with which one is able...

Microbial transport and fate in the subsurface: An introduction to the special collection

USDA-ARS?s Scientific Manuscript database

Microorganisms constitute the almost exclusive form of life in the earth’s subsurface (not including caves), particularly at depths exceeding the soil horizon. While of broad interest to ecology and geology, scientific interest in the fate and transport of microorganisms, particularly those introduc...

Integrated surface/subsurface permafrost thermal hydrology: Model formulation and proof-of-concept simulations

DOE PAGES

Painter, Scott L.; Coon, Ethan T.; Atchley, Adam L.; ...

2016-08-11

The need to understand potential climate impacts and feedbacks in Arctic regions has prompted recent interest in modeling of permafrost dynamics in a warming climate. A new fine-scale integrated surface/subsurface thermal hydrology modeling capability is described and demonstrated in proof-of-concept simulations. The new modeling capability combines a surface energy balance model with recently developed three-dimensional subsurface thermal hydrology models and new models for nonisothermal surface water flows and snow distribution in the microtopography. Surface water flows are modeled using the diffusion wave equation extended to include energy transport and phase change of ponded water. Variation of snow depth in themore » microtopography, physically the result of wind scour, is also modeled heuristically with a diffusion wave equation. The multiple surface and subsurface processes are implemented by leveraging highly parallel community software. Fully integrated thermal hydrology simulations on the tilted open book catchment, an important test case for integrated surface/subsurface flow modeling, are presented. Fine-scale 100-year projections of the integrated permafrost thermal hydrological system on an ice wedge polygon at Barrow Alaska in a warming climate are also presented. Finally, these simulations demonstrate the feasibility of microtopography-resolving, process-rich simulations as a tool to help understand possible future evolution of the carbon-rich Arctic tundra in a warming climate.« less

Reactive Transport Modeling of Microbe-mediated Fe (II) Oxidation for Enhanced Oil Recovery

NASA Astrophysics Data System (ADS)

Surasani, V.; Li, L.

2011-12-01

Microbially Enhanced Oil Recovery (MEOR) aims to improve the recovery of entrapped heavy oil in depleted reservoirs using microbe-based technology. Reservoir ecosystems often contain diverse microbial communities those can interact with subsurface fluids and minerals through a network of nutrients and energy fluxes. Microbe-mediated reactions products include gases, biosurfactants, biopolymers those can alter the properties of oil and interfacial interactions between oil, brine, and rocks. In addition, the produced biomass and mineral precipitates can change the reservoir permeability profile and increase sweeping efficiency. Under subsurface conditions, the injection of nitrate and Fe (II) as the electron acceptor and donor allows bacteria to grow. The reaction products include minerals such as Fe(OH)3 and nitrogen containing gases. These reaction products can have large impact on oil and reservoir properties and can enhance the recovery of trapped oil. This work aims to understand the Fe(II) oxidation by nitrate under conditions relevant to MEOR. Reactive transport modeling is used to simulate the fluid flow, transport, and reactions involved in this process. Here we developed a complex reactive network for microbial mediated nitrate-dependent Fe (II) oxidation that involves both thermodynamic controlled aqueous reactions and kinetic controlled Fe (II) mineral reaction. Reactive transport modeling is used to understand and quantify the coupling between flow, transport, and reaction processes. Our results identify key parameter controls those are important for the alteration of permeability profile under field conditions.

Evaluation of a genome-scale in silico metabolic model for Geobacter metallireducens by using proteomic data from a field biostimulation experiment.

PubMed

Fang, Yilin; Wilkins, Michael J; Yabusaki, Steven B; Lipton, Mary S; Long, Philip E

2012-12-01

Accurately predicting the interactions between microbial metabolism and the physical subsurface environment is necessary to enhance subsurface energy development, soil and groundwater cleanup, and carbon management. This study was an initial attempt to confirm the metabolic functional roles within an in silico model using environmental proteomic data collected during field experiments. Shotgun global proteomics data collected during a subsurface biostimulation experiment were used to validate a genome-scale metabolic model of Geobacter metallireducens-specifically, the ability of the metabolic model to predict metal reduction, biomass yield, and growth rate under dynamic field conditions. The constraint-based in silico model of G. metallireducens relates an annotated genome sequence to the physiological functions with 697 reactions controlled by 747 enzyme-coding genes. Proteomic analysis showed that 180 of the 637 G. metallireducens proteins detected during the 2008 experiment were associated with specific metabolic reactions in the in silico model. When the field-calibrated Fe(III) terminal electron acceptor process reaction in a reactive transport model for the field experiments was replaced with the genome-scale model, the model predicted that the largest metabolic fluxes through the in silico model reactions generally correspond to the highest abundances of proteins that catalyze those reactions. Central metabolism predicted by the model agrees well with protein abundance profiles inferred from proteomic analysis. Model discrepancies with the proteomic data, such as the relatively low abundances of proteins associated with amino acid transport and metabolism, revealed pathways or flux constraints in the in silico model that could be updated to more accurately predict metabolic processes that occur in the subsurface environment.

Discriminative Random Field Models for Subsurface Contamination Uncertainty Quantification

NASA Astrophysics Data System (ADS)

Arshadi, M.; Abriola, L. M.; Miller, E. L.; De Paolis Kaluza, C.

2017-12-01

Application of flow and transport simulators for prediction of the release, entrapment, and persistence of dense non-aqueous phase liquids (DNAPLs) and associated contaminant plumes is a computationally intensive process that requires specification of a large number of material properties and hydrologic/chemical parameters. Given its computational burden, this direct simulation approach is particularly ill-suited for quantifying both the expected performance and uncertainty associated with candidate remediation strategies under real field conditions. Prediction uncertainties primarily arise from limited information about contaminant mass distributions, as well as the spatial distribution of subsurface hydrologic properties. Application of direct simulation to quantify uncertainty would, thus, typically require simulating multiphase flow and transport for a large number of permeability and release scenarios to collect statistics associated with remedial effectiveness, a computationally prohibitive process. The primary objective of this work is to develop and demonstrate a methodology that employs measured field data to produce equi-probable stochastic representations of a subsurface source zone that capture the spatial distribution and uncertainty associated with key features that control remediation performance (i.e., permeability and contamination mass). Here we employ probabilistic models known as discriminative random fields (DRFs) to synthesize stochastic realizations of initial mass distributions consistent with known, and typically limited, site characterization data. Using a limited number of full scale simulations as training data, a statistical model is developed for predicting the distribution of contaminant mass (e.g., DNAPL saturation and aqueous concentration) across a heterogeneous domain. Monte-Carlo sampling methods are then employed, in conjunction with the trained statistical model, to generate realizations conditioned on measured borehole data. Performance of the statistical model is illustrated through comparisons of generated realizations with the `true' numerical simulations. Finally, we demonstrate how these realizations can be used to determine statistically optimal locations for further interrogation of the subsurface.

An Inverse Analysis Approach to the Characterization of Chemical Transport in Paints

PubMed Central

Willis, Matthew P.; Stevenson, Shawn M.; Pearl, Thomas P.; Mantooth, Brent A.

2014-01-01

The ability to directly characterize chemical transport and interactions that occur within a material (i.e., subsurface dynamics) is a vital component in understanding contaminant mass transport and the ability to decontaminate materials. If a material is contaminated, over time, the transport of highly toxic chemicals (such as chemical warfare agent species) out of the material can result in vapor exposure or transfer to the skin, which can result in percutaneous exposure to personnel who interact with the material. Due to the high toxicity of chemical warfare agents, the release of trace chemical quantities is of significant concern. Mapping subsurface concentration distribution and transport characteristics of absorbed agents enables exposure hazards to be assessed in untested conditions. Furthermore, these tools can be used to characterize subsurface reaction dynamics to ultimately design improved decontaminants or decontamination procedures. To achieve this goal, an inverse analysis mass transport modeling approach was developed that utilizes time-resolved mass spectroscopy measurements of vapor emission from contaminated paint coatings as the input parameter for calculation of subsurface concentration profiles. Details are provided on sample preparation, including contaminant and material handling, the application of mass spectrometry for the measurement of emitted contaminant vapor, and the implementation of inverse analysis using a physics-based diffusion model to determine transport properties of live chemical warfare agents including distilled mustard (HD) and the nerve agent VX. PMID:25226346

Scaling Effects of Cr(VI) Reduction Kinetics. The Role of Geochemical Heterogeneity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Li; Li, Li

2015-10-22

The natural subsurface is highly heterogeneous with minerals distributed in different spatial patterns. Fundamental understanding of how mineral spatial distribution patterns regulate sorption process is important for predicting the transport and fate of chemicals. Existing studies about the sorption was carried out in well-mixed batch reactors or uniformly packed columns, with few data available on the effects of spatial heterogeneities. As a result, there is a lack of data and understanding on how spatial heterogeneities control sorption processes. In this project, we aim to understand and develop modeling capabilities to predict the sorption of Cr(VI), an omnipresent contaminant in naturalmore » systems due to its natural occurrence and industrial utilization. We systematically examine the role of spatial patterns of illite, a common clay, in determining the extent of transport limitation and scaling effects associated with Cr(VI) sorption capacity and kinetics using column experiments and reactive transport modeling. Our results showed that the sorbed mass and rates can differ by an order of magnitude due to of the illite spatial heterogeneities and transport limitation. With constraints from data, we also developed the capabilities of modeling Cr(VI) in heterogeneous media. The developed model is then utilized to understand the general principles that govern the relationship between sorption and connectivity, a key measure of the spatial pattern characteristics. This correlation can be used to estimate Cr(VI) sorption characteristics in heterogeneous porous media. Insights gained here bridge gaps between laboratory and field application in hydrogeology and geochemical field, and advance predictive understanding of reactive transport processes in the natural heterogeneous subsurface. We believe that these findings will be of interest to a large number of environmental geochemists and engineers, hydrogeologists, and those interested in contaminant fate and transport, water quality and water composition, and natural attenuation processes in natural systems.« less

Development of concepts for the management of thermal resources in urban areas - Assessment of transferability from the Basel (Switzerland) and Zaragoza (Spain) case studies

NASA Astrophysics Data System (ADS)

Epting, Jannis; García-Gil, Alejandro; Huggenberger, Peter; Vázquez-Suñe, Enric; Mueller, Matthias H.

2017-05-01

The shallow subsurface in urban areas is increasingly used by shallow geothermal energy systems as a renewable energy resource and as a cheap cooling medium, e.g. for building air conditioning. In combination with further anthropogenic activities, this results in altered thermal regimes in the subsurface and the so-called subsurface urban heat island effect. Successful thermal management of urban groundwater resources requires understanding the relative contributions of the different thermal parameters and boundary conditions that result in the "present thermal state" of individual urban groundwater bodies. To evaluate the "present thermal state" of urban groundwater bodies, good quality data are required to characterize the hydraulic and thermal aquifer parameters. This process also involved adequate monitoring systems which provide consistent subsurface temperature measurements and are the basis for parameterizing numerical heat-transport models. This study is based on previous work already published for two urban groundwater bodies in Basel (CH) and Zaragoza (ES), where comprehensive monitoring networks (hydraulics and temperature) as well as calibrated high-resolution numerical flow- and heat-transport models have been analyzed. The "present thermal state" and how it developed according to the different hydraulic and thermal boundary conditions is compared to a "potential natural state" in order to assess the anthropogenic thermal changes that have already occurred in the urban groundwater bodies we investigated. This comparison allows us to describe the various processes concerning groundwater flow and thermal regimes for the different urban settings. Furthermore, the results facilitate defining goals for specific aquifer regions, including future aquifer use and urbanization, as well as evaluating the thermal use potential for these regions. As one example for a more sustainable thermal use of subsurface water resources, we introduce the thermal management concept of the "relaxation factor", which is a first approach to overcome the present policy of "first come, first served". Remediation measures to regenerate overheated urban aquifers are also introduced. The transferability of the applied methods to other urban areas is discussed. It is shown that an appropriate selection of locations for monitoring hydraulic and thermal boundary conditions make it possible to implement representative interpretations of groundwater flow and thermal regimes as well as to set up high-resolution numerical flow- and heat-transport models. Those models are the basis for the sustainable management of thermal resources.

Eddy-induced transport of the Kuroshio warm water around the Ryukyu Islands in the East China Sea

NASA Astrophysics Data System (ADS)

Kamidaira, Yuki; Uchiyama, Yusuke; Mitarai, Satoshi

2017-07-01

In this study, an oceanic downscaling model in a double-nested configuration was used to investigate the role played by the Kuroshio warm current in preserving and maintaining biological diversity in the coral coasts around the Ryukyu Islands (Japan). A comparison of the modeled data demonstrated that the innermost submesoscale eddy-resolving model successfully reproduced the synoptic and mesoscale oceanic structures even without data assimilation. The Kuroshio flows on the shelf break of the East China Sea approximately 150-200 km from the islands; therefore, eddy-induced transient processes are essential to the lateral transport of material within the strip between the Kuroshio and the islands. The model indicated an evident predominance of submesoscale anticyclonic eddies over cyclonic eddies near the surface of this strip. An energy conversion analysis relevant to the eddy-generation mechanisms revealed that a combination of both the shear instability due to the Kuroshio and the topography and baroclinic instability around the Kuroshio front jointly provoke these near-surface anticyclonic eddies, as well as the subsurface cyclonic eddies that are shed around the shelf break. Both surface and subsurface eddies fit within the submesoscale, and they are energized more as the grid resolution of the model is increased. An eddy heat flux (EHF) analysis was performed with decomposition into the divergent (dEHF) and rotational (rEHF) components. The rEHF vectors appeared along the temperature variance contours by following the Kuroshio, whereas the dEHF properly measured the transverse transport normal to the Kuroshio's path. The diagnostic EHF analysis demonstrated that an asymmetric dEHF occurs within the surface mixed layer, which promotes eastward transport toward the islands. Conversely, below the mixed layer, a negative dEHF tongue is formed that promotes the subsurface westward warm water transport.

The genome of Geobacter bemidjiensis, exemplar for the subsurface clade of Geobacter species that predominate in Fe(III)-reducing subsurface environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aklujkar, Muktak; Young, Nelson D; Holmes, Dawn

2010-01-01

Background. Geobacter species in a phylogenetic cluster known as subsurface clade 1 are often the predominant microorganisms in subsurface environments in which Fe(III) reduction is the primary electron-accepting process. Geobacter bemidjiensis, a member of this clade, was isolated from hydrocarbon-contaminated subsurface sediments in Bemidji, Minnesota, and is closely related to Geobacter species found to be abundant at other subsurface sites. This study examines whether there are significant differences in the metabolism and physiology of G. bemidjiensis compared to non-subsurface Geobacter species. Results. Annotation of the genome sequence of G. bemidjiensis indicates several differences in metabolism compared to previously sequenced non-subsurfacemore » Geobacteraceae, which will be useful for in silico metabolic modeling of subsurface bioremediation processes involving Geobacter species. Pathways can now be predicted for the use of various carbon sources such as propionate by G. bemidjiensis. Additional metabolic capabilities such as carbon dioxide fixation and growth on glucose were predicted from the genome annotation. The presence of different dicarboxylic acid transporters and two oxaloacetate decarboxylases in G. bemidjiensis may explain its ability to grow by disproportionation of fumarate. Although benzoate is the only aromatic compound that G. bemidjiensis is known or predicted to utilize as an electron donor and carbon source, the genome suggests that this species may be able to detoxify other aromatic pollutants without degrading them. Furthermore, G. bemidjiensis is auxotrophic for 4-aminobenzoate, which makes it the first Geobacter species identified as having a vitamin requirement. Several features of the genome indicated that G. bemidjiensis has enhanced abilities to respire, detoxify and avoid oxygen. Conclusion. Overall, the genome sequence of G. bemidjiensis offers surprising insights into the metabolism and physiology of Geobacteraceae in subsurface environments, compared to non-subsurface Geobacter species, such as the ability to disproportionate fumarate, more efficient oxidation of propionate, enhanced responses to oxygen stress, and dependence on the environment for a vitamin requirement. Therefore, an understanding of the activity of Geobacter species in the subsurface is more likely to benefit from studies of subsurface isolates such as G. bemidjiensis than from the non-subsurface model species studied so far.« less

Thermal–moisture dynamics of embankments with asphalt pavement in permafrost regions of central Tibetan Plateau

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wen, Zhi; Zhang, Mingli; Ma, Wei

Subsurface moisture content is one of the critical factors that control the thermal dynamics of embankments. However, information on the subsurface moisture movement and distribution in embankments is still limited. To better understand the coupled water and heat transport within embankments, subsurface temperature and moisture of an asphalt pavement highway were extensively measured from 2009 to 2011. Collected data indicate that pure heat conduction is the overall main mechanism of heat transport in the embankment and heat convection plays a relatively unimportant role in heat transport. The results also indicate that subsurface moisture and temperature dynamics in the asphalt layermore » is strongly related to the rainfall events, while the subsurface moisture content below the road base course maintains relatively constant. Rainfall in summer leads to rapid cooling of the subsurface soil. Our results suggest that frequent and small rainfall events favour the thermal stability of the embankment due to the loss of latent heat of water evaporation. Moisture migration during freezing still occurred in the gravel fill and the water infiltrated into the active layer during thawing period. Freezing-induced water migration may result in the increase in water content of the embankment and the decrease in compactness of gravel fill.« less

Sorption of Pseudomonas putida onto differently structured kaolinite minerals

NASA Astrophysics Data System (ADS)

Vasiliadou, I. A.; Papoulis, D.; Chrysikopoulos, C.; Panagiotaras, D.; Karakosta, E.; Fardis, M.; Papavassiliou, G.

2010-12-01

The presence of bio-colloids (e.g. bacteria and viruses) in the subsurface could be attributed to the release of particles from septic tanks, broken sewer lines or from artificial recharge with treated municipal wastewater. Bio-colloid transport in the subsurface is significantly affected by sorption onto the solid matrix. Bio-colloid attachment onto mobile or suspended in the aqueous phase soil particles (e.g. clay or other minerals) also may influence their fate and transport in the subsurface. The present study focuses on the investigation of Pseudomonas (Ps.) putida sorption onto well (KGa-1) and poorly (KGa-2) crystallized kaolinite minerals. Batch experiments were carried out to determine the sorption isotherms of Ps. putida onto both types of kaolinite particles. The sorption process of Ps. putida onto KGa-1 and KGa-2 is adequately described by a Langmuir isotherm. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy as well as Nuclear Magnetic Resonance were employed to study the sorption mechanisms of Ps. putida. Experimental results indicated that KGa-2 presented higher affinity and sorption capacity than KGa-1. It was shown that electrostatic interactions and structural disorders can influence the sorption capacity of clay particles.

Reply to 'Comment on kinetic modeling of microbially-driven redox chemistry of subsurface environments: coupling transport, microbial metabolism and geochemistry' by J. Griffioen

NASA Astrophysics Data System (ADS)

Hunter, K. S.; Van Cappellen, P.

2000-01-01

Our paper, 'Kinetic modeling of microbially-driven redox chemistry of subsurface environments: coupling transport, microbial metabolism and geochemistry' (Hunter et al., 1998), presents a theoretical exploration of biogeochemical reaction networks and their importance to the biogeochemistry of groundwater systems. As with any other model, the kinetic reaction-transport model developed in our paper includes only a subset of all physically, biologically and chemically relevant processes in subsurface environments. It considers aquifer systems where the primary energy source driving microbial activity is the degradation of organic matter. In addition to the primary biodegradation pathways of organic matter (i.e. respiration and fermentation), the redox chemistry of groundwaters is also affected by reactions not directly involving organic matter oxidation. We refer to the latter as secondary reactions. By including secondary redox reactions which consume reduced reaction products (e.g., Mn2+, FeS, H2S), and in the process compete with microbial heterotrophic populations for available oxidants (i.e. O2, NO3-, Mn(IV), Fe(III), SO42-), we predict spatio-temporal distributions of microbial activity which differ significantly from those of models which consider only the biodegradation reactions. That is, the secondary reactions have a significant impact on the distributions of the rates of heterotrophic and chemolithotrophic metabolic pathways. We further show that secondary redox reactions, as well as non-redox reactions, significantly influence the acid-base chemistry of groundwaters. The distributions of dissolved inorganic redox species along flowpaths, however, are similar in simulations with and without secondary reactions (see Figs. 3(b) and 7(b) in Hunter et al., 1998), indicating that very different biogeochemical reaction dynamics may lead to essentially the same chemical redox zonation of a groundwater system.

Assessment of electrical conductivity as a surrogate measurement for water samples in a tracer injection experiment

USDA-ARS?s Scientific Manuscript database

The transport behavior of solutes in streams depends on chemical, physical, biological, and hydrodynamic processes. Although it is a very complex system, it is known that this behavior is greatly influenced by surface and subsurface flows. For this reason, tracer injection in the water flows is one ...

Nested sparse grid collocation method with delay and transformation for subsurface flow and transport problems

NASA Astrophysics Data System (ADS)

Liao, Qinzhuo; Zhang, Dongxiao; Tchelepi, Hamdi

2017-06-01

In numerical modeling of subsurface flow and transport problems, formation properties may not be deterministically characterized, which leads to uncertainty in simulation results. In this study, we propose a sparse grid collocation method, which adopts nested quadrature rules with delay and transformation to quantify the uncertainty of model solutions. We show that the nested Kronrod-Patterson-Hermite quadrature is more efficient than the unnested Gauss-Hermite quadrature. We compare the convergence rates of various quadrature rules including the domain truncation and domain mapping approaches. To further improve accuracy and efficiency, we present a delayed process in selecting quadrature nodes and a transformed process for approximating unsmooth or discontinuous solutions. The proposed method is tested by an analytical function and in one-dimensional single-phase and two-phase flow problems with different spatial variances and correlation lengths. An additional example is given to demonstrate its applicability to three-dimensional black-oil models. It is found from these examples that the proposed method provides a promising approach for obtaining satisfactory estimation of the solution statistics and is much more efficient than the Monte-Carlo simulations.

The Multi-Scale Mass Transfer Processes Controlling Natural Attenuation and Engineered Remediation: An IFC Focused on Hanford’s 300 Area Uranium Plume Quality Assurance Project Plan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fix, N. J.

The purpose of the project is to conduct research at an Integrated Field-Scale Research Challenge Site in the Hanford Site 300 Area, CERCLA OU 300-FF-5 (Figure 1), to investigate multi-scale mass transfer processes associated with a subsurface uranium plume impacting both the vadose zone and groundwater. The project will investigate a series of science questions posed for research related to the effect of spatial heterogeneities, the importance of scale, coupled interactions between biogeochemical, hydrologic, and mass transfer processes, and measurements/approaches needed to characterize a mass-transfer dominated system. The research will be conducted by evaluating three (3) different hypotheses focused onmore » multi-scale mass transfer processes in the vadose zone and groundwater, their influence on field-scale U(VI) biogeochemistry and transport, and their implications to natural systems and remediation. The project also includes goals to 1) provide relevant materials and field experimental opportunities for other ERSD researchers and 2) generate a lasting, accessible, and high-quality field experimental database that can be used by the scientific community for testing and validation of new conceptual and numerical models of subsurface reactive transport.« less

Recent developments and emergent challenges in Ecohydrology: Focus on the belowground frontier

NASA Astrophysics Data System (ADS)

Mackay, D. S.

2017-12-01

The broad spectrum of ecohydrology issues touch on many areas of research in hydrology. But what are the emerging themes and challenges that represent the core of ecohydrology as a maturing discipline? To answer this question the ecohydrology lens was applied to manuscripts published in Water Resources Research over period of 2015 through July 2017. The 235 manuscripts retrieved can be broadly grouped into catchment hydrology, riparian-hyporheic-stream processes, critical zone, land-atmosphere exchange, wetlands, and sustainability. Three dominant crosscutting themes (i.e., coevolution, interfaces, and energy exchange) account for more than half the papers retrieved. In the context of ecohydrology, coevolution refers to the development of physical systems in concert with biological systems and their interactions. In an ecohydrology context, interfaces refer to subsurface, and sometime surface connections that influence transport (e.g., solutes concentration-discharge) influenced by vegetative plumbing, ecophysiology, animal behavior, and microbial processes. Energy exchange in ecohydrology connects vegetative processes to movement of water to the atmosphere through evapotranspiration. Across these themes there is emerging theory and methodology that emphasizes the integrated roles of biology and hydrology in the subsurface. In particular, there is a notable surge of interest in the role of plant roots on subsurface processes. But these are hard to observe and remain challenging to model. By adopting principles of coevolution, in particular, significant advances will be made in modeling plant roots and their depths, corroborated with new geophysical and tracer tools, for improving understanding of critical zone development, subsurface flow processes, and land-atmosphere energy exchange.

Assessing the Potential Consequences of Subsurface Bioremediation: Fe-oxide Bioreductive Processes and the Propensity for Contaminant-colloid Co-transport and Media Structural Breakdown

DTIC Science & Technology

2017-05-12

were resolved by a technical approach that included three well-integrated experimental tasks follows: Task A: Quantify the impact of time- dependent ...aggregate breakdown and colloid dispersion depending on the extent of Fe(III) reduction and altered the pore structure and chemical reactivity of the porous...have significant effect on the transport of molecular and colloidal tracers (but not on the ionic tracer Br-) and colloid generation depending on

Time series analysis of contaminant transport in the subsurface: applications to conservative tracer and engineered nanomaterials.

PubMed

Bai, Chunmei; Li, Yusong

2014-08-01

Accurately predicting the transport of contaminants in the field is subject to multiple sources of uncertainty due to the variability of geological settings, the complexity of field measurements, and the scarcity of data. Such uncertainties can be amplified when modeling some emerging contaminants, such as engineered nanomaterials, when a fundamental understanding of their fate and transport is lacking. Typical field work includes collecting concentration at a certain location for an extended period of time, or measuring the movement of plume for an extended period time, which would result in a time series of observation data. This work presents an effort to evaluate the possibility of applying time series analysis, particularly, autoregressive integrated moving average (ARIMA) models, to forecast contaminant transport and distribution in the subsurface environment. ARIMA modeling was first assessed in terms of its capability to forecast tracer transport at two field sites, which had different levels of heterogeneity. After that, this study evaluated the applicability of ARIMA modeling to predict the transport of engineered nanomaterials at field sites, including field measured data of nanoscale zero valent iron and (nZVI) and numerically generated data for the transport of nano-fullerene aggregates (nC60). This proof-of-concept effort demonstrates the possibility of applying ARIMA to predict the contaminant transport in the subsurface environment. Like many other statistical models, ARIMA modeling is only descriptive and not explanatory. The limitation and the challenge associated with applying ARIMA modeling to contaminant transport in the subsurface are also discussed. Copyright © 2014 Elsevier B.V. All rights reserved.

Time series analysis of contaminant transport in the subsurface: Applications to conservative tracer and engineered nanomaterials

NASA Astrophysics Data System (ADS)

Bai, Chunmei; Li, Yusong

2014-08-01

Accurately predicting the transport of contaminants in the field is subject to multiple sources of uncertainty due to the variability of geological settings, the complexity of field measurements, and the scarcity of data. Such uncertainties can be amplified when modeling some emerging contaminants, such as engineered nanomaterials, when a fundamental understanding of their fate and transport is lacking. Typical field work includes collecting concentration at a certain location for an extended period of time, or measuring the movement of plume for an extended period time, which would result in a time series of observation data. This work presents an effort to evaluate the possibility of applying time series analysis, particularly, autoregressive integrated moving average (ARIMA) models, to forecast contaminant transport and distribution in the subsurface environment. ARIMA modeling was first assessed in terms of its capability to forecast tracer transport at two field sites, which had different levels of heterogeneity. After that, this study evaluated the applicability of ARIMA modeling to predict the transport of engineered nanomaterials at field sites, including field measured data of nanoscale zero valent iron and (nZVI) and numerically generated data for the transport of nano-fullerene aggregates (nC60). This proof-of-concept effort demonstrates the possibility of applying ARIMA to predict the contaminant transport in the subsurface environment. Like many other statistical models, ARIMA modeling is only descriptive and not explanatory. The limitation and the challenge associated with applying ARIMA modeling to contaminant transport in the subsurface are also discussed.

The Effects of Subsurface Bioremediation on Soil Structure, Colloid Formation, and Contaminant Transport

NASA Astrophysics Data System (ADS)

Wang, Y.; Liang, X.; Zhuang, J.; Radosevich, M.

2016-12-01

Anaerobic bioremediation is widely applied to create anaerobic subsurface conditions designed to stimulate microorganisms that degrade organic contaminants and immobilize toxic metals in situ. Anaerobic conditions that accompany such techniques also promotes microbially mediated Fe(III)-oxide mineral reduction. The reduction of Fe(III) could potentially cause soil structure breakdown, formation of clay colloids, and alternation of soil surface chemical properties. These processes could then affect bioremediation and the migration of contaminants. Column experiments were conducted to investigate the impact of anaerobic bioreduction on soil structure, hydraulic properties, colloid formation, and transport of three tracers (bromide, DFBA, and silica shelled silver nanoparticles). Columns packed with inoculated water stable soil aggregates were placed in anaerobic glovebox, and artificial groundwater media was pumped into the columns to simulate anaerobic bioreduction process for four weeks. Decent amount of soluble Fe(II) accompanied by colloids were detected in the effluent from bioreduction columns a week after initiation of bioreduction treatment, which demonstrated bioreduction of Fe(III) and formation of colloids. Transport experiments were performed in the columns before and after bioreduction process to assess the changes of hydraulic and surface chemical properties through bioreduction treatment. Earlier breakthrough of bromide and DFBA after treatment indicated alterations in flow paths (formation of preferential flow paths). Less dispersion of bromide and DFBA, and less tailing of DFBA after treatment implied breakdown of soil aggregates. Dramatically enhanced transport and early breakthrough of silica shelled silver nanoparticles after treatment supported the above conclusion of alterations in flow paths, and indicated changes of soil surface chemical properties.

A field study of colloid transport in surface and subsurface flows

NASA Astrophysics Data System (ADS)

Zhang, Wei; Tang, Xiang-Yu; Xian, Qing-Song; Weisbrod, Noam; Yang, Jae E.; Wang, Hong-Lan

2016-11-01

Colloids have been recognized to enhance the migration of strongly-sorbing contaminants. However, few field investigations have examined combined colloid transport via surface runoff and subsurface flows. In a headwater catchment of the upper Yangtze River, a 6 m (L) by 4 m (W) sloping (6°) farmland plot was built by cement walls to form no-flow side boundaries. The plot was monitored in the summer of 2014 for the release and transport of natural colloids via surface runoff and subsurface flows (i.e., the interflow from the soil-mudrock interface and fracture flow from the mudrock-sandstone interface) in response to rain events. The water sources of the subsurface flows were apportioned to individual rain events using a two end-member model (i.e., mobile pre-event soil water extracted by a suction-cup sampler vs. rainwater (event water)) based on δ18O measurements. For rain events with high preceding soil moisture, mobile pre-event soil water was the main contributor (generally >60%) to the fracture flow. The colloid concentration in the surface runoff was 1-2 orders of magnitude higher than that in the subsurface flows. The lowest colloid concentration was found in the subsurface interflow, which was probably the result of pore-scale colloid straining mechanisms. The rainfall intensity and its temporal variation govern the dynamics of the colloid concentrations in both surface runoff and subsurface flows. The duration of the antecedent dry period affected not only the relative contributions of the rainwater and the mobile pre-event soil water to the subsurface flows but also the peak colloid concentration, particularly in the fracture flow. The <10 μm fine colloid size fraction accounted for more than 80% of the total suspended particles in the surface runoff, while the colloid size distributions of both the interflow and the fracture flow shifted towards larger diameters. These results highlight the need to avoid the application of strongly-sorbing agrochemicals (e.g., pesticides, phosphorus fertilizers) immediately before rainfall following a long no-rain period because their transport in association with colloids may occur rapidly over long distances via both surface runoff and subsurface flows with rainfall.

Mesh infrastructure for coupled multiprocess geophysical simulations

DOE PAGES

Garimella, Rao V.; Perkins, William A.; Buksas, Mike W.; ...

2014-01-01

We have developed a sophisticated mesh infrastructure capability to support large scale multiphysics simulations such as subsurface flow and reactive contaminant transport at storage sites as well as the analysis of the effects of a warming climate on the terrestrial arctic. These simulations involve a wide range of coupled processes including overland flow, subsurface flow, freezing and thawing of ice rich soil, accumulation, redistribution and melting of snow, biogeochemical processes involving plant matter and finally, microtopography evolution due to melting and degradation of ice wedges below the surface. In addition to supporting the usual topological and geometric queries about themore » mesh, the mesh infrastructure adds capabilities such as identifying columnar structures in the mesh, enabling deforming of the mesh subject to constraints and enabling the simultaneous use of meshes of different dimensionality for subsurface and surface processes. The generic mesh interface is capable of using three different open source mesh frameworks (MSTK, MOAB and STKmesh) under the hood allowing the developers to directly compare them and choose one that is best suited for the application's needs. We demonstrate the results of some simulations using these capabilities as well as present a comparison of the performance of the different mesh frameworks.« less

Chemotaxis and flow disorder shape microbial dispersion in porous media

NASA Astrophysics Data System (ADS)

De Anna, Pietro; Yawata, Yutaka; Stocker, Roman; Juanes, Ruben

2017-04-01

Bacteria drive a plethora of natural processes in the subsurface, consuming organic matter and catalysing chemical reactions that are key to global elemental cycles. These macro-scale consequences result from the collective action of individual bacteria at the micro-scale, which are modulated by the highly heterogeneous subsurface environment, dominated by flow disorder and strong chemical gradients. Yet, despite the generally recognized importance of these microscale processes, microbe-host medium interaction at the pore scale remain poorly characterized and understood. Here, we introduce a microfluidic model system to directly image and quantify the role of cell motility on bacterial dispersion and residence time in confined, porous, media. Using the soil-dwelling bacterium Bacillus subtilis and the common amino acid serine as a resource, we observe that chemotaxis in highly disordered and confined physico-chemical environment affords bacteria an increase in their ability to persistently occupy the host medium. Our findings illustrate that the interplay between bacterial behaviour and pore-scale disorder in fluid velocity and nutrient concentration directly impacts the residence time, transport and bio-geo-chemical transformation rates of biota in the subsurface, and thus likely the processes they mediate.

3DHYDROGEOCHEM: A 3-DIMENSIONAL MODEL OF DENSITY-DEPENDENT SUBSURFACE FLOW AND THERMAL MULTISPECIES-MULTICOMPONENT HYDROGEOCHEMICAL TRANSPORT (EPA/600/SR-98/159)

EPA Science Inventory

This report presents a three-dimensional finite-element numerical model designed to simulate chemical transport in subsurface systems with temperature effect taken into account. The three-dimensional model is developed to provide (1) a tool of application, with which one is able ...

A simple model for remineralization of subsurface lesions in tooth enamel

NASA Astrophysics Data System (ADS)

Christoffersen, J.; Christoffersen, M. R.; Arends, J.

1982-12-01

A model for remineralization of subsurface lesions in tooth enamel is presented. The important assumption on which the model is based is that the rate-controlling process is the crystal surface process by which ions are incorporated in the crystallites; that is, the transport of ions through small holes in the so-called intact surface layer does not influence the rate of mineral uptake at the crystal surface. Further, the density of mineral in the lesion is assumed to increase down the lesion, when the remineralization process is started. It is shown that the dimension of the initial holes in the enamel surface layer must be larger than the dimension of the individual crystallites in order to prevent the formation of arrested lesions. Theoretical expressions for the progress of remineralization are given. The suggested model emphasizes the need for measurements of mineral densities in the lesion, prior to, and during the lesion repair.

Scenario simulation based assessment of subsurface energy storage

NASA Astrophysics Data System (ADS)

Beyer, C.; Bauer, S.; Dahmke, A.

2014-12-01

Energy production from renewable sources such as solar or wind power is characterized by temporally varying power supply. The politically intended transition towards renewable energies in Germany („Energiewende") hence requires the installation of energy storage technologies to compensate for the fluctuating production. In this context, subsurface energy storage represents a viable option due to large potential storage capacities and the wide prevalence of suited geological formations. Technologies for subsurface energy storage comprise cavern or deep porous media storage of synthetic hydrogen or methane from electrolysis and methanization, or compressed air, as well as heat storage in shallow or moderately deep porous formations. Pressure build-up, fluid displacement or temperature changes induced by such operations may affect local and regional groundwater flow, geomechanical behavior, groundwater geochemistry and microbiology. Moreover, subsurface energy storage may interact and possibly be in conflict with other "uses" like drinking water abstraction or ecological goods and functions. An utilization of the subsurface for energy storage therefore requires an adequate system and process understanding for the evaluation and assessment of possible impacts of specific storage operations on other types of subsurface use, the affected environment and protected entities. This contribution presents the framework of the ANGUS+ project, in which tools and methods are developed for these types of assessments. Synthetic but still realistic scenarios of geological energy storage are derived and parameterized for representative North German storage sites by data acquisition and evaluation, and experimental work. Coupled numerical hydraulic, thermal, mechanical and reactive transport (THMC) simulation tools are developed and applied to simulate the energy storage and subsurface usage scenarios, which are analyzed for an assessment and generalization of the imposed THMC-processes, mutual effects and influences on protected entities. The scenario analyses allow the deduction of monitoring concepts as well as a first methodology for large scale spatial planning of the geological subsurface. This concept is illustrated for different storage options and their impacts in space and time.

A model for the hydrologic and climatic behavior of water on Mars

NASA Technical Reports Server (NTRS)

Clifford, Stephen M.

1993-01-01

An analysis is carried out of the hydrologic response of a water-rich Mars to climate change and to the physical and thermal evolution of its crust, with particular attention given to the potential role of the subsurface transport, assuming that the current models of insolation-driven change describe reasonably the atmospheric leg of the planet's long-term hydrologic cycle. Among the items considered are the thermal and hydrologic properties of the crust, the potential distribution of ground ice and ground water, the stability and replenishment of equatorial ground ice, basal melting and the polar mass balance, the thermal evolution of the early cryosphere, the recharge of the valley networks and outflow, and several processes that are likely to drive the large-scale vertical and horizontal transport of H2O within the crust. The results lead to the conclusion that subsurface transport has likely played an important role in the geomorphic evolution of the Martian surface and the long-term cycling of H2O between the atmosphere, polar caps, and near-surface crust.

Design and testing of a process-based groundwater vulnerability assessment (P-GWAVA) system for predicting concentrations of agrichemicals in groundwater across the United States

USGS Publications Warehouse

Barbash, Jack E; Voss, Frank D.

2016-03-29

Efforts to assess the likelihood of groundwater contamination from surface-derived compounds have spanned more than three decades. Relatively few of these assessments, however, have involved the use of process-based simulations of contaminant transport and fate in the subsurface, or compared the predictions from such models with measured data—especially over regional to national scales. To address this need, a process-based groundwater vulnerability assessment (P-GWAVA) system was constructed to use transport-and-fate simulations to predict the concentration of any surface-derived compound at a specified depth in the vadose zone anywhere in the conterminous United States. The system was then used to simulate the concentrations of selected agrichemicals in the vadose zone beneath agricultural areas in multiple locations across the conterminous United States. The simulated concentrations were compared with measured concentrations of the compounds detected in shallow groundwater (that is, groundwater drawn from within a depth of 6.3 ± 0.5 meters [mean ± 95 percent confidence interval] below the water table) in more than 1,400 locations across the United States. The results from these comparisons were used to select the simulation approaches that led to the closest agreement between the simulated and the measured concentrations.The P-GWAVA system uses computer simulations that account for a broader range of the hydrologic, physical, biological and chemical phenomena known to control the transport and fate of solutes in the subsurface than has been accounted for by any other vulnerability assessment over regional to national scales. Such phenomena include preferential transport and the influences of temperature, soil properties, and depth on the partitioning, transport, and transformation of pesticides in the subsurface. Published methods and detailed soil property data are used to estimate a wide range of model input parameters for each site, including surface albedo, surface crust permeability, soil water content, Brooks-Corey parameters, saturated hydraulic conductivity, macroporosity and sizes of microbial populations, as well as solute partition coefficients, reaction rates, and meso-micropore diffusion rates. To ensure geographic consistency among the predictions, the only site-specific input data that are used are those that are available for all of the 48 conterminous states.

Nutrient loss in leachate and surface runoff from surface-broadcast and subsurface-banded broiler litter

USDA-ARS?s Scientific Manuscript database

Subsurface band application of poultry litter has been shown to reduce the transport of nutrients from fields in surface runoff, compared to the conventional surface broadcast application. Little in situ research has been conducted to determine effects of surface broadcast application and subsurfac...

Fate and Transport of Nanoparticles in Porous Media: A Numerical Study

NASA Astrophysics Data System (ADS)

Taghavy, Amir

Understanding the transport characteristics of NPs in natural soil systems is essential to revealing their potential impact on the food chain and groundwater. In addition, many nanotechnology-based remedial measures require effective transport of NPs through soil, which necessitates accurate understanding of their transport and retention behavior. Based upon the conceptual knowledge of environmental behavior of NPs, mathematical models can be developed to represent the coupling of processes that govern the fate of NPs in subsurface, serving as effective tools for risk assessment and/or design of remedial strategies. This work presents an innovative hybrid Eulerian-Lagrangian modeling technique for simulating the simultaneous reactive transport of nanoparticles (NPs) and dissolved constituents in porous media. Governing mechanisms considered in the conceptual model include particle-soil grain, particle-particle, particle-dissolved constituents, and particle- oil/water interface interactions. The main advantage of this technique, compared to conventional Eulerian models, lies in its ability to address non-uniformity in physicochemical particle characteristics. The developed numerical simulator was applied to investigate the fate and transport of NPs in a number of practical problems relevant to the subsurface environment. These problems included: (1) reductive dechlorination of chlorinated solvents by zero-valent iron nanoparticles (nZVI) in dense non-aqueous phase liquid (DNAPL) source zones; (2) reactive transport of dissolving silver nanoparticles (nAg) and the dissolved silver ions; (3) particle-particle interactions and their effects on the particle-soil grain interactions; and (4) influence of particle-oil/water interface interactions on NP transport in porous media.

Subsurface phosphorus transport through a no-till field in the semi arid Palouse region

NASA Astrophysics Data System (ADS)

Norby, J. C.; Brooks, E. S.; Strawn, D. G.

2017-12-01

Excess application of fertilizers containing nitrogen and phosphorus for farming use has led to ongoing water quality issues in the United States. When these nutrients leave agronomic systems, and enter water bodies in large quantities, algal bloom and eutrophication can occur. Extensive studies focusing on phosphorus as a pollutant from agronomic systems have been conducted in the many regions of the United States; however, there has been a lack of studies completed in the semiarid Palouse region of eastern Washington and western Idaho. The goal of this research study was to better understand how no-till farm management has altered soil P temporally and the current availability for off-site transport of P throughout an artificially drained catchment at the Cook Agronomy Farm in Pullman, WA. We also attempted to determine the processes responsible for subsurface flow of phosphorus, specifically through preferential flow pathways. Dissolved reactive P (DRP)concentrations of subsurface drainage from a artificial drain exceeded TMDL threshold concentrations during numerous seasonal high flow events over the two-year study time frame. Soil analyses show a highly variable distribution of water-extractable P across the sub-catchment area and initial results suggest a translocation of P species deeper into the soil profile after implementing no-till practices in 1998. We hypothesized that a greater network of macropores from lack of soil disturbance allow for preferential flow of nutrient-laden water deeper into the subsurface and to the artificial drain system. Simulated flow experiments on soil cores from the study site showed large-scale macropore development, extreme variability in soil conductivity, and high P adsorption potential for the soils, suggesting a disconnect between P movement through macropore soil and subsurface drainage water rich in DRP at the artificial drain line outlet.

Modeling Coupled Movement of Water, Vapor, and Energy in Soils and at the Soil-Atmosphere Interface Using HYDRUS

NASA Astrophysics Data System (ADS)

Simunek, Jiri; Brunetti, Giuseppe; Saito, Hirotaka; Bristow, Keith

2017-04-01

Mass and energy fluxes in the subsurface are closely coupled and cannot be evaluated without considering their mutual interactions. However, only a few numerical models consider coupled water, vapor and energy transport in both the subsurface and at the soil-atmosphere interface. While hydrological and thermal processes in the subsurface are commonly implemented in existing models, which often consider both isothermally and thermally induced water and vapor flow, the interactions at the soil-atmosphere interface are often simplified, and the effects of slope inclination, slope azimuth, variable surface albedo and plant shading on incoming radiation and spatially variable surface mass and energy balance, and consequently on soil moisture and temperature distributions, are rarely considered. In this presentation we discuss these missing elements and our attempts to implement them into the HYDRUS model. We demonstrate implications of some of these interactions and their impact on the spatial distributions of soil temperature and water content, and their effect on soil evaporation. Additionally, we will demonstrate the use of the HYDRUS model to simulate processes relevant to the ground source heat pump systems.

Utilizing High-Performance Computing to Investigate Parameter Sensitivity of an Inversion Model for Vadose Zone Flow and Transport

NASA Astrophysics Data System (ADS)

Fang, Z.; Ward, A. L.; Fang, Y.; Yabusaki, S.

2011-12-01

High-resolution geologic models have proven effective in improving the accuracy of subsurface flow and transport predictions. However, many of the parameters in subsurface flow and transport models cannot be determined directly at the scale of interest and must be estimated through inverse modeling. A major challenge, particularly in vadose zone flow and transport, is the inversion of the highly-nonlinear, high-dimensional problem as current methods are not readily scalable for large-scale, multi-process models. In this paper we describe the implementation of a fully automated approach for addressing complex parameter optimization and sensitivity issues on massively parallel multi- and many-core systems. The approach is based on the integration of PNNL's extreme scale Subsurface Transport Over Multiple Phases (eSTOMP) simulator, which uses the Global Array toolkit, with the Beowulf-Cluster inspired parallel nonlinear parameter estimation software, BeoPEST in the MPI mode. In the eSTOMP/BeoPEST implementation, a pre-processor generates all of the PEST input files based on the eSTOMP input file. Simulation results for comparison with observations are extracted automatically at each time step eliminating the need for post-process data extractions. The inversion framework was tested with three different experimental data sets: one-dimensional water flow at Hanford Grass Site; irrigation and infiltration experiment at the Andelfingen Site; and a three-dimensional injection experiment at Hanford's Sisson and Lu Site. Good agreements are achieved in all three applications between observations and simulations in both parameter estimates and water dynamics reproduction. Results show that eSTOMP/BeoPEST approach is highly scalable and can be run efficiently with hundreds or thousands of processors. BeoPEST is fault tolerant and new nodes can be dynamically added and removed. A major advantage of this approach is the ability to use high-resolution geologic models to preserve the spatial structure in the inverse model, which leads to better parameter estimates and improved predictions when using the inverse-conditioned realizations of parameter fields.

Contamination and restoration of groundwater aquifers.

PubMed Central

Piver, W T

1993-01-01

Humans are exposed to chemicals in contaminated groundwaters that are used as sources of drinking water. Chemicals contaminate groundwater resources as a result of waste disposal methods for toxic chemicals, overuse of agricultural chemicals, and leakage of chemicals into the subsurface from buried tanks used to hold fluid chemicals and fuels. In the process, both the solid portions of the subsurface and the groundwaters that flow through these porous structures have become contaminated. Restoring these aquifers and minimizing human exposure to the parent chemicals and their degradation products will require the identification of suitable biomarkers of human exposure; better understandings of how exposure can be related to disease outcome; better understandings of mechanisms of transport of pollutants in the heterogeneous structures of the subsurface; and field testing and evaluation of methods proposed to restore and cleanup contaminated aquifers. In this review, progress in these many different but related activities is presented. PMID:8354172

Determination of thermodynamic and transport parameters of naphthenic acids and organic process chemicals in oil sand tailings pond water.

PubMed

Wang, Xiaomeng; Robinson, Lisa; Wen, Qing; Kasperski, Kim L

2013-07-01

Oil sand tailings pond water contains naphthenic acids and process chemicals (e.g., alkyl sulphates, quaternary ammonium compounds, and alkylphenol ethoxylates). These chemicals are toxic and can seep through the foundation of the tailings pond to the subsurface, potentially affecting the quality of groundwater. As a result, it is important to measure the thermodynamic and transport parameters of these chemicals in order to study the transport behavior of contaminants through the foundation as well as underground. In this study, batch adsorption studies and column experiments were performed. It was found that the transport parameters of these chemicals are related to their molecular structures and other properties. The computer program (CXTFIT) was used to further evaluate the transport process in the column experiments. The results from this study show that the transport of naphthenic acids in a glass column is an equilibrium process while the transport of process chemicals seems to be a non-equilibrium process. At the end of this paper we present a real-world case study in which the transport of the contaminants through the foundation of an external tailings pond is calculated using the lab-measured data. The results show that long-term groundwater monitoring of contaminant transport at the oil sand mining site may be necessary to avoid chemicals from reaching any nearby receptors.

DNA-labeled micro- and nanoparticles: a new approach to study contaminant transport in the subsurface

NASA Astrophysics Data System (ADS)

McNew, C.; Wang, C.; Kocis, T. N.; Murphy, N. P.; Dahlke, H. E.

2017-12-01

Though our understanding of contaminant behavior in the subsurface has improved, our ability to measure and predict complex contaminant transport pathways at hillslope to watershed scales is still lacking. By utilizing bio-molecular nanotechnology developed for nano-medicines and drug delivery, we are able to produce DNA-labeled micro- and nanoparticles for use in a myriad of environmental systems. Control of the fabrication procedure allows us to produce particles of custom size, charge, and surface functionality to mimic the transport properties of the particulate contaminant or colloid of interest. The use of custom sequenced DNA allows for the fabrication of an enormous number of unique particle labels (approximately 1.61 x 1060 unique sequences) and the ability to discern between varied spatial and temporal applications, or the transport effect of varied particle size, charge, or surface properties. To date, this technology has been utilized to study contaminant transport from lab to field scales, including surface and open channel flow applications, transport in porous media, soil retention, and even subglacial flow pathways. Here, we present the technology for production and detection of the DNA-labeled particles along with the results from a current hillslope study at the Sierra Foothills Research and Extension Center (SFREC). This field study utilizes spatial and temporal variations in DNA-labeled particle applications to identify subsurface pollutant transport pathways through the four distinct soil horizons present at the SFREC site. Results from this and previous studies highlight the tremendous potential of the DNA-labeled particle technology for studying contaminant transport through the subsurface.

Impact of Scale-Dependent Coupled Processes on Solute Fate and Transport in the Critical Zone: Case Studies Involving Inorganic and Radioactive Contaminants

NASA Astrophysics Data System (ADS)

Jardine, P. M.; Gentry, R. W.

2011-12-01

Soil, the thin veneer of matter covering the Earths surface that supports a web of living diversity, is often abused through anthropogenic inputs of toxic waste. This subsurface regime, coupled with life sustaining surface water and groundwater is known as the "Critical Zone". The disposal of radioactive and toxic organic and inorganic waste generated by industry and various government agencies has historically involved shallow land burial or the use of surface impoundments in unsaturated soils and sediments. Presently, contaminated sites have been closing rapidly and many remediation strategies have chosen to leave contaminants in-place. As such, contaminants will continue to interact with the geosphere and investigations on long term changes and interactive processes is imperative to verify risks. In this presentation we provide a snap-shot of subsurface science research from the past 25 y that seeks to provide an improved understanding and predictive capability of multi-scale contaminant fate and transport processes in heterogeneous unsaturated and saturated environments. Investigations focus on coupled hydrological, geochemical, and microbial processes that control reactive contaminant transport and that involve multi-scale fundamental research ranging from the molecular scale (e.g. synchrotrons, electron sources, arrays) to in situ plume interrogation strategies at the macroscopic scale (e.g. geophysics, field biostimulation, coupled processes monitoring). We show how this fundamental research is used to provide multi-process, multi-scale predictive monitoring and modeling tools that can be used at contaminated sites to (1) inform and improve the technical basis for decision making, and (2) assess which sites are amenable to natural attenuation and which would benefit from source zone remedial intervention.

A new technology for determining transport parameters in porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Conca, J.L.; Wright, J.

The UFA Method can directly and rapidly measure transport parameters for any porous medium over a wide range of water contents and conditions. UFA results for subsurface sediments at a mixed-waste disposal site at the Hanford Site in Washington State provided the data necessary for detailed hydrostratigraphic mapping, subsurface flux and recharge distributions, and subsurface chemical mapping. Seven hundred unsaturated conductivity measurements along with pristine pore water extractions were obtained in only six months using the UFA. These data are used to provide realistic information to conceptual models, predictive models and restoration strategies.

A laboratory study of colloid and solute transport in surface runoff on saturated soil

NASA Astrophysics Data System (ADS)

Yu, Congrong; Gao, Bin; Muñoz-Carpena, Rafael; Tian, Yuan; Wu, Lei; Perez-Ovilla, Oscar

2011-05-01

SummaryColloids in surface runoff may pose risks to the ecosystems not only because some of them (e.g., pathogens) are toxic, but also because they may facilitate the transport of other contaminants. Although many studies have been conducted to explore colloid fate and transport in the environment, current understanding of colloids in surface runoff is still limited. In this study, we conducted a range of laboratory experiments to examine the transport behavior of colloids in a surface runoff system, made of a soil box packed with quartz sand with four soil drainage outlets and one surface flow outlet. A natural clay colloid (kaolinite) and a conservative chemical tracer (bromide) were applied to the system under a simulated rainfall event (64 mm/h). Effluent soil drainage and surface flow samples were collected to determine the breakthrough concentrations of bromide and kaolinite. Under the experimental conditions tested, our results showed that surface runoff dominated the transport processes. As a result, kaolinite and bromide were found more in surface flow than in soil drainage. Comparisons between the breakthrough concentrations of bromide and kaolinite showed that kaolinite had lower mobility than bromide in the subsurface flow (i.e., soil drainage), but behaved almost identical to bromide in the surface runoff. Student's t-test confirmed the difference between kaolinite and bromide in subsurface flow ( p = 0.02). Spearman's test and linear regression analysis, however, showed a strong 1:1 correlation between kaolinite and bromide in surface runoff ( p < 0.0001). Our result indicate that colloids and chemical solutes may behave similarly in overland flow on bare soils with limited drainage when surface runoff dominates the transport processes.

Adapting HYDRUS-1D to Simulate Overland Flow and Reactive Transport During Sheet Flow Deviations

NASA Astrophysics Data System (ADS)

Liang, J.; Bradford, S. A.; Simunek, J.; Hartmann, A.

2017-12-01

The HYDRUS-1D code is a popular numerical model for solving the Richards equation for variably-saturated water flow and solute transport in porous media. This code was adapted to solve rather than the Richards equation for subsurface flow the diffusion wave equation for overland flow at the soil surface. The numerical results obtained by the new model produced an excellent agreement with the analytical solution of the kinematic wave equation. Model tests demonstrated its applicability to simulate the transport and fate of many different solutes, such as non-adsorbing tracers, nutrients, pesticides, and microbes. However, the diffusion wave or kinematic wave equations describe surface runoff as sheet flow with a uniform depth and velocity across the slope. In reality, overland water flow and transport processes are rarely uniform. Local soil topography, vegetation, and spatial soil heterogeneity control directions and magnitudes of water fluxes, and strongly influence runoff characteristics. There is increasing evidence that variations in soil surface characteristics influence the distribution of overland flow and transport of pollutants. These spatially varying surface characteristics are likely to generate non-equilibrium flow and transport processes. HYDRUS-1D includes a hierarchical series of models of increasing complexity to account for both physical equilibrium and non-equilibrium, e.g., dual-porosity and dual-permeability models, up to a dual-permeability model with immobile water. The same conceptualization as used for the subsurface was implemented to simulate non-equilibrium overland flow and transport at the soil surface. The developed model improves our ability to describe non-equilibrium overland flow and transport processes and to improves our understanding of factors that cause this behavior. The HYDRUS-1D overland flow and transport model was additionally also extended to simulate soil erosion. The HYDRUS-1D Soil Erosion Model has been verified by comparing with other soil erosion models. The model performed well when the average soil particle size is relatively large. The performance of the soil erosion model has been further validated by comparing with selected experimental datasets from the literature.

LLNL SFA OBER SBR FY17 Program Management and Performance Report: Subsurface Biogeochemistry of Actinides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kersting, Annie B.

A major scientific challenge in environmental sciences is to identify the dominant processes controlling actinide transport in the environment. It is estimated that currently, over 2200 metric tons of anthropogenic plutonium (Pu) has accumulated worldwide, a number that increases yearly with additional spent nuclear fuel (Ewing et al., 2010). Plutonium has been shown to migrate on the scale of kilometers, giving way to a critical concern that the fundamental biogeochemical processes that control its behavior in the subsurface are not well understood (Kersting et al. 1999; Novikov et al. 2006; Santschi et al. 2002). Neptunium (Np) is less prevalent inmore » the environment; however, it is predicted to be a significant long-term dose contributor in high-level nuclear waste. Our focus on Np chemistry in this Science Plan is intended to help formulate a better understanding of Pu redox transformations in the environment and clarify the differences between the two long-lived actinides. The research approach of our Science Plan combines (1) Fundamental Mechanistic Studies that identify and quantify biogeochemical processes that control actinide behavior in solution and on solids, (2) Field Integration Studies that investigate the transport characteristics of Pu and test our conceptual understanding of actinide transport, and (3) Actinide Research Capabilities that allow us to achieve the objectives of this Scientific Focus Area (SFA) and provide new opportunities for advancing actinide environmental chemistry. These three Research Thrusts form the basis of our SFA Science Program.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kersting, Annie B.; Zavarin, Mavrik

A major scientific challenge in environmental sciences is to identify the dominant processes controlling actinide transport in the environment. It is estimated that currently, over 2200 metric tons of plutonium (Pu) have been deposited in the subsurface worldwide, a number that increases yearly with additional spent nuclear fuel (Ewing et al., 2010). Plutonium has been shown to migrate on the scale of kilometers, giving way to a critical concern that the fundamental biogeochemical processes that control its behavior in the subsurface are not well understood (Kersting et al., 1999; Novikov et al., 2006; Santschi et al., 2002). Neptunium (Np) ismore » less prevalent in the environment; however, it is predicted to be a significant long-term dose contributor in high-level nuclear waste. Our focus on Np chemistry in this Science Plan is intended to help formulate a better understanding of Pu redox transformations in the environment and clarify the differences between the two long-lived actinides. The research approach of our Science Plan combines (1) Fundamental Mechanistic Studies that identify and quantify biogeochemical processes that control actinide behavior in solution and on solids, (2) Field Integration Studies that investigate the transport characteristics of Pu and test our conceptual understanding of actinide transport, and (3) Actinide Research Capabilities that allow us to achieve the objectives of this Scientific Focus Area (SFA and provide new opportunities for advancing actinide environmental chemistry. These three Research Thrusts form the basis of our SFA Science Program (Figure 1).« less

Discharge-nitrate data clustering for characterizing surface-subsurface flow interaction and calibration of a hydrologic model

NASA Astrophysics Data System (ADS)

Shrestha, R. R.; Rode, M.

2008-12-01

Concentration of reactive chemicals has different chemical signatures in baseflow and surface runoff. Previous studies on nitrate export from a catchment indicate that the transport processes are driven by subsurface flow. Therefore nitrate signature can be used for understanding the event and pre-event contributions to streamflow and surface-subsurface flow interactions. The study uses flow and nitrate concentration time series data for understanding the relationship between these two variables. Unsupervised artificial neural network based learning method called self organizing map is used for the identification of clusters in the datasets. Based on the cluster results, five different pattern in the datasets are identified which correspond to (i) baseflow, (ii) subsurface flow increase, (iii) surface runoff increase, (iv) surface runoff recession, and (v) subsurface flow decrease regions. The cluster results in combination with a hydrologic model are used for discharge separation. For this purpose, a multi-objective optimization tool NSGA-II is used, where violation of cluster results is used as one of the objective functions. The results show that the use of cluster results as supplementary information for the calibration of a hydrologic model gives a plausible simulation of subsurface flow as well total runoff at the catchment outlet. The study is undertaken using data from the Weida catchment in the North-Eastern Germany, which is a sub-catchment of the Weisse Elster river in the Elbe river basin.

Nutrient transport through a Vegetative Filter Strip with subsurface drainage.

PubMed

Bhattarai, Rabin; Kalita, Prasanta Kumar; Patel, Mita Kanu

2009-04-01

The transport of nutrients and soil sediments in runoff has been recognized as a noteworthy environmental issue. Vegetative Filter Strips (VFS) have been used as one of the best management practices (BMPs) for retaining nutrients and sediments from surface runoff, thus preventing the pollutants from reaching receiving waters. However, the effectiveness of a VFS when combined with a subsurface drainage system has not been investigated previously. This study was undertaken to monitor the retention and transport of nutrients within a VFS that had a subsurface drainage system installed at a depth of 1.2 m below the soil surface. Nutrient concentrations of NO(3)-N (Nitrate Nitrogen), PO(-)(4) (Orthophosphorus), and TP (Total Phosphorus) were measured in surface water samples (entering and leaving the VFS), and subsurface outflow. Soil samples were collected and analyzed for plant available Phosphorus (Bray P1) and NO(3)-N concentrations. Results showed that PO(-)(4), NO(3)-N, and TP concentrations decreased in surface flow through the VFS. Many surface outflow water samples from the VFS showed concentration reductions of as much as 75% for PO(-)(4) and 70% for TP. For subsurface outflow water samples through the drainage system, concentrations of PO(-)(4) and TP decreased but NO(3)-N concentrations increased in comparison to concentrations in surface inflow samples. Soil samples that were collected from various depths in the VFS showed a minimal buildup of nutrients in the top soil profile but indicated a gradual buildup of nutrients at the depth of the subsurface drain. Results demonstrate that although a VFS can be very effective in reducing runoff and nutrients from surface flow, the presence of a subsurface drain underneath the VFS may not be environmentally beneficial. Such a combination may increase NO(3)-N transport from the VFS, thus invalidating the purpose of the BMP.

Microbially Mediated Kinetic Sulfur Isotope Fractionation: Reactive Transport Modeling Benchmark

NASA Astrophysics Data System (ADS)

Wanner, C.; Druhan, J. L.; Cheng, Y.; Amos, R. T.; Steefel, C. I.; Ajo Franklin, J. B.

2014-12-01

Microbially mediated sulfate reduction is a ubiquitous process in many subsurface systems. Isotopic fractionation is characteristic of this anaerobic process, since sulfate reducing bacteria (SRB) favor the reduction of the lighter sulfate isotopologue (S32O42-) over the heavier isotopologue (S34O42-). Detection of isotopic shifts have been utilized as a proxy for the onset of sulfate reduction in subsurface systems such as oil reservoirs and aquifers undergoing uranium bioremediation. Reactive transport modeling (RTM) of kinetic sulfur isotope fractionation has been applied to field and laboratory studies. These RTM approaches employ different mathematical formulations in the representation of kinetic sulfur isotope fractionation. In order to test the various formulations, we propose a benchmark problem set for the simulation of kinetic sulfur isotope fractionation during microbially mediated sulfate reduction. The benchmark problem set is comprised of four problem levels and is based on a recent laboratory column experimental study of sulfur isotope fractionation. Pertinent processes impacting sulfur isotopic composition such as microbial sulfate reduction and dispersion are included in the problem set. To date, participating RTM codes are: CRUNCHTOPE, TOUGHREACT, MIN3P and THE GEOCHEMIST'S WORKBENCH. Preliminary results from various codes show reasonable agreement for the problem levels simulating sulfur isotope fractionation in 1D.

Use of an uncertainty analysis for genome-scale models as a prediction tool for microbial growth processes in subsurface environments.

PubMed

Klier, Christine

2012-03-06

The integration of genome-scale, constraint-based models of microbial cell function into simulations of contaminant transport and fate in complex groundwater systems is a promising approach to help characterize the metabolic activities of microorganisms in natural environments. In constraint-based modeling, the specific uptake flux rates of external metabolites are usually determined by Michaelis-Menten kinetic theory. However, extensive data sets based on experimentally measured values are not always available. In this study, a genome-scale model of Pseudomonas putida was used to study the key issue of uncertainty arising from the parametrization of the influx of two growth-limiting substrates: oxygen and toluene. The results showed that simulated growth rates are highly sensitive to substrate affinity constants and that uncertainties in specific substrate uptake rates have a significant influence on the variability of simulated microbial growth. Michaelis-Menten kinetic theory does not, therefore, seem to be appropriate for descriptions of substrate uptake processes in the genome-scale model of P. putida. Microbial growth rates of P. putida in subsurface environments can only be accurately predicted if the processes of complex substrate transport and microbial uptake regulation are sufficiently understood in natural environments and if data-driven uptake flux constraints can be applied.

Development of monitoring and modelling tools as basis for sustainable thermal management concepts of urban groundwater bodies

NASA Astrophysics Data System (ADS)

Mueller, Matthias H.; Epting, Jannis; Köhler, Mandy; Händel, Falk; Huggenberger, Peter

2015-04-01

Increasing groundwater temperatures observed in many urban areas strongly interfere with the demand of thermal groundwater use. The groundwater temperatures in these urban areas are affected by numerous interacting factors: open and closed-loop geothermal systems for heating and cooling, sealed surfaces, constructions in the subsurface (infrastructure and buildings), artificial groundwater recharge, and interaction with rivers. On the one hand, these increasing groundwater temperatures will negatively affect the potential for its use in the future e.g. for cooling purposes. On the other hand, elevated subsurface temperatures can be considered as an energy source for shallow geothermal heating systems. Integrated thermal management concepts are therefore needed to coordinate the thermal use of groundwater in urban areas. These concepts should be based on knowledge of the driving processes which influence the thermal regime of the aquifer. We are currently investigating the processes influencing the groundwater temperature throughout the urban area of Basel City, Switzerland. This involves a three-dimensional numerical groundwater heat-transport model including geothermal use and interactions with the unsaturated zone such as subsurface constructions reaching into the aquifer. The cantonal groundwater monitoring system is an important part of the data base in our model, which will help to develop sustainable management strategies. However, single temperature measurements in conventional groundwater wells can be biased by vertical thermal convection. Therefore, multilevel observation wells are used in the urban areas of the city to monitor subsurface temperatures reaching from the unsaturated zone to the base of the aquifer. These multilevel wells are distributed in a pilot area in order to monitor the subsurface temperatures in the vicinity of deep buildings and to quantify the influence of the geothermal use of groundwater. Based on time series of the conventional groundwater wells, the multilevel observation wells and the different boundary conditions we characterize the groundwater temperature regimes using a regional groundwater heat-transport model. In the urban area of Basel, mean annual groundwater temperatures are significantly increasing with 0.05 K per year in the period of 1994 to 2014, which is most likely due to anthropogenic influences. Overall, mean annual groundwater temperatures of Basel are 3.0

Investigation of off-site airborne transport of lead from a superfund removal action site using lead isotope ratios and concentrations

USGS Publications Warehouse

Pribil, Michael J.; Maddaloni, Mark A.; Staiger, Kimberly; Wilson, Eric; Magriples, Nick; Ali, Mustafa; Santella, Dennis

2014-01-01

Lead (Pb) concentration and Pb isotopic composition of surface and subsurface soil samples were used to investigate the potential for off-site air transport of Pb from a former white Pb processing facility to neighboring residential homes in a six block area on Staten Island, NY. Surface and subsurface soil samples collected on the Jewett White Pb site were found to range from 1.122 to 1.138 for 206Pb/207Pb and 2.393 to 2.411 for 208Pb/207Pb. The off-site surface soil samples collected from residential backyards, train trestle, near site grass patches and background areas varied from 1.144 to 1.196 for 206Pb/207Pb and 2.427 to 2.464 for 208Pb/207Pb. Two soil samples collected along Richmond Terrace, where Jewett site soils accumulated after major rain events, varied from 1.136 to 1.147 for 206Pb/207Pb and 2.407 to 2.419 for 208Pb/207Pb. Lead concentration for on-site surface soil samples ranged from 450 to 8000 ug/g, on-site subsurface soil samples ranged from 90,000 to 240,000 ug/g and off-site samples varied from 380 to 3500 ug/g. Lead concentration and isotopic composition for the Staten Island off-site samples were similar to previously published data for other northeastern US cities and reflect re-suspension and re-mobilization of local accumulated Pb. The considerable differences in both the Pb isotopic composition and Pb concentration of on-site and off-site samples resulted in the ability to geochemically trace the transport of particulate Pb. Data in this study indicate minimal off-site surface transport of Pb from the Jewett site into the neighboring residential area.

Radiogenic isotopic approaches for quantifying radionuclide transport (Invited)

NASA Astrophysics Data System (ADS)

Maher, K.; Depaolo, D. J.; Singleton, M. J.; Christensen, J. N.; Conrad, M. E.

2009-12-01

Naturally occurring variations in the isotopic compositions of U and Sr provide unique opportunities for assessing the fate and transport of radionuclides at field-scale conditions. When coupled with reactive transport models, U and Sr isotopes may also provide additional constraints on the rates of sediment-fluid or sediment-waste interactions. Such isotopic approaches can be useful for sites where subsurface characterization is complicated by a lack of accessibility or the presence of substantial heterogeneity. In addition, a variety of quantitative modeling approaches of different complexity can be used to evaluate experimentally determined parameters for radionuclide mobility at the field-scale. At the Hanford Site in eastern Washington, 87Sr/86Sr and 234U/238U ratios have been used to quantify the residence time of Sr and U in the unsaturated zone, the long-term background infiltration rate through the unsaturated zone, and to assess the influence of enhanced wastewater discharge on the regional unconfined aquifer. As a result of different processing techniques or due to interactions between caustic waste and the natural sediment, waste plumes may also inherit isotopic fingerprints (e.g. 234U/238U, 235U/238U, 236U/238U; δ15N & δ18O of nitrate) that can be used to resolve multiple sources of contamination. Finally, enriched isotopic tracers can be applied to experimental manipulations to assess the retardation of a variety of contaminants. Collectively this isotopic data contributes unique perspectives on both the hydrologic conditions across the site and the mobility of key radionuclides. Predicting the long-term fate and transport of radionuclides in the environment is often challenging due to natural heterogeneity and incomplete characterization of the subsurface, however detailed analysis of isotopic variations can provide one additional means of characterizing the subsurface.

Assessing the potential contributions of additional retention processes to PFAS retardation in the subsurface.

PubMed

Brusseau, Mark L

2018-02-01

A comprehensive understanding of the transport and fate of per- and poly-fluoroalkyl substances (PFAS) in the subsurface is critical for accurate risk assessments and design of effective remedial actions. A multi-process retention model is proposed to account for potential additional sources of retardation for PFAS transport in source zones. These include partitioning to the soil atmosphere, adsorption at air-water interfaces, partitioning to trapped organic liquids (NAPL), and adsorption at NAPL-water interfaces. An initial assessment of the relative magnitudes and significance of these retention processes was conducted for two PFAS of primary concern, perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), and an example precursor (fluorotelomer alcohol, FTOH). The illustrative evaluation was conducted using measured porous-medium properties representative of a sandy vadose-zone soil. Data collected from the literature were used to determine measured or estimated values for the relevant distribution coefficients, which were in turn used to calculate retardation factors for the model system. The results showed that adsorption at the air-water interface was a primary source of retention for both PFOA and PFOS, contributing approximately 50% of total retention for the conditions employed. Adsorption to NAPL-water interfaces and partitioning to bulk NAPL were also shown to be significant sources of retention. NAPL partitioning was the predominant source of retention for FTOH, contributing ~98% of total retention. These results indicate that these additional processes may be, in some cases, significant sources of retention for subsurface transport of PFAS. The specific magnitudes and significance of the individual retention processes will depend upon the properties and conditions of the specific system of interest (e.g., PFAS constituent and concentration, porous medium, aqueous chemistry, fluid saturations, co-contaminants). In cases wherein these additional retention processes are significant, retardation of PFAS in source areas would likely be greater than what is typically estimated based on the standard assumption of solid-phase adsorption as the sole retention mechanism. This has significant ramifications for accurate determination of the migration potential and magnitude of mass flux to groundwater, as well as for calculations of contaminant mass residing in source zones. Both of which have critical implications for human-health risk assessments. Copyright © 2017 Elsevier B.V. All rights reserved.

Laboratory experiments on solute transport in bimodal porous media under cyclic precipitation-evaporation boundary conditions

NASA Astrophysics Data System (ADS)

Cremer, Clemens; Neuweiler, Insa

2016-04-01

Flow and solute transport in the shallow subsurface is strongly governed by atmospheric boundary conditions. Erratically varying infiltration and evaporation cycles lead to alternating upward and downward flow, as well as spatially and temporally varying water contents and associated hydraulic conductivity of the prevailing materials. Thus presenting a highly complicated, dynamic system. Knowledge of subsurface solute transport processes is vital to assess e.g. the entry of, potentially hazardous, solutes to the groundwater and nutrient uptake by plant roots and can be gained in many ways. Besides field measurements and numerical simulations, physical laboratory experiments represent a way to establish process understanding and furthermore validate numerical schemes. With the aim to gain a better understanding and to quantify solute transport in the unsaturated shallow subsurface under natural precipitation conditions in heterogeneous media, we conduct physical laboratory experiments in a 22 cm x 8 cm x 1 cm flow cell that is filled with two types of sand and apply cyclic infiltration-evaporation phases at the soil surface. Pressure at the bottom of the domain is kept constant. Following recent studies (Lehmann and Or, 2009; Bechtold et al., 2011a), heterogeneity is introduced by a sharp vertical interface between coarse and fine sand. Fluorescent tracers are used to i) qualitatively visualize transport paths within the domain and ii) quantify solute leaching at the bottom of the domain. Temporal and spatial variations in water content during the experiment are derived from x-ray radiographic images. Monitored water contents between infiltration and evaporation considerably changed in the coarse sand while the fine sand remained saturated throughout the experiments. Lateral solute transport through the interface in both directions at different depths of the investigated soil columns were observed. This depended on the flow rate applied at the soil surface and significantly influenced solute leaching. Dynamic boundary conditions generally resulted in faster initial breakthrough and stronger tailing. References: Bechtold, M., S. Haber-Pohlmeier, J. Vanderborght, A. Pohlmeier, T.P.A. Ferré and H. Veerecken. 2011a. Near-surface solute redistribution during evaporation. Geophys. Res. Lett., 38, L17404, doi:10.1029/2011GL048147. Lehmann, P. and D. Or. 2009. Evaporation and capillary coupling across vertical textural contrasts in porous media. Phys. Rev. E, 80, 046318, doi:10.1103/PhysRevE.80.046318.

Factors Effecting the Fate and Transport of CL-20 in the Vadose Zone and Groundwater: Final Report 2002 - 2004 SERDP Project CP-1255

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szecsody, James E.; Riley, Robert G.; Devary, Brooks J.

2005-06-01

This SERDP-funded project was initiated to investigate the fate of CL-20 in the subsurface environment, with a focus on identification and quantification of geochemical and microbial reactions of CL-20. CL-20 can be released to the surface and subsurface terrestrial environment by: a) manufacturing processes, b) munition storage, and c) use with low order detonation or unexploded ordnance. The risk of far-field subsurface migration was assessed through labora-tory experiments with a variety of sediments and subsurface materials to quantify processes that control CL-20 sorption-limited migration and degradation. Results of this study show that CL-20 will exhibit differing behavior in the subsurfacemore » terrestrial environment: 1. CL-20 on the sediment surface will photodegrade and interact with plants/animals (described in other SERDP projects CU 1254, 1256). CL-20 will exhibit greater sorption in humid sediments to organic matter. Transport will be solubility limited (i.e., low CL-20 aqueous solubility). 2. CL-20 infiltration into soils (<2 m) from spills will be subject to sorption to soil organic matter (if present), and low to high biodegradation rates (weeks to years) depending on the microbial population (greater in humid environment). 3. CL-20 in the vadose zone (>2 m) will be, in most cases, subject to low sorption and low degradation rates, so would persist in the subsurface environment and be at risk for deep migration. Low water content in arid regions will result in a decrease in both sorption and the degradation rate. Measured degradation rates in unsaturated sediments of years would result in significant subsurface migration distances. 4. CL-20 in groundwater will be subject to some sorption but likely very slow degradation rates. CL-20 sorption will be greater than RDX. Most CL-20 degradation will be abiotic (ferrous iron and other transition metals), because most deep subsurface systems have extremely low natural microbial populations. Degradation rates will range from weeks (iron reducing systems) to years. Although CL-20 will move rapidly through most sediments in the terrestrial environment, subsurface remediation can be utilized for cleanup. Transformation of CL-20 to intermediates can be rapidly accomplished under: a) reducing conditions (CL-20 4.1 min. half-life, RDX 18 min. half-life), b) alkaline (pH >10) conditions, and c) bioremediation with added nutrients. CL-20 degradation to intermediates may be insufficient to mitigate environmental impact, as the toxicity of many of these compounds is unknown. Biostimulation in oxic to reducing systems by carbon and nutrient addition can mineralize CL-20, with the most rapid rates occurring under reducing conditions.« less

PCR detection of groundwater bacteria associated with colloidal transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cruz-Perez, P.; Stetzenbach, L.D.; Alvarez, A.J.

1996-02-29

Colloidal transport may increase the amount of contaminant material than that which could be transported by water flow alone. The role of colloids in groundwater contaminant transport is complicated and may involve many different processes, including sorption of elements onto colloidal particles, coagulation/dissolution, adsorption onto solid surfaces, filtration, and migration. Bacteria are known to concentrate minerals and influence the transport of compounds in aqueous environments and may also serve as organic colloids, thereby influencing subsurface transport of radionuclides and other contaminants. The initial phase of the project consisted of assembling a list of bacteria capable of sequestering or facilitating mineralmore » transport. The development and optimization of the PCR amplification assay for the detection of the organisms of interest, and the examination of regional groundwaters for those organisms, are presented for subsequent research.« less

SUTRA: A model for 2D or 3D saturated-unsaturated, variable-density ground-water flow with solute or energy transport

USGS Publications Warehouse

Voss, Clifford I.; Provost, A.M.

2002-01-01

SUTRA (Saturated-Unsaturated Transport) is a computer program that simulates fluid movement and the transport of either energy or dissolved substances in a subsurface environment. This upgraded version of SUTRA adds the capability for three-dimensional simulation to the former code (Voss, 1984), which allowed only two-dimensional simulation. The code employs a two- or three-dimensional finite-element and finite-difference method to approximate the governing equations that describe the two interdependent processes that are simulated: 1) fluid density-dependent saturated or unsaturated ground-water flow; and 2) either (a) transport of a solute in the ground water, in which the solute may be subject to: equilibrium adsorption on the porous matrix, and both first-order and zero-order production or decay; or (b) transport of thermal energy in the ground water and solid matrix of the aquifer. SUTRA may also be used to simulate simpler subsets of the above processes. A flow-direction-dependent dispersion process for anisotropic media is also provided by the code and is introduced in this report. As the primary calculated result, SUTRA provides fluid pressures and either solute concentrations or temperatures, as they vary with time, everywhere in the simulated subsurface system. SUTRA flow simulation may be employed for two-dimensional (2D) areal, cross sectional and three-dimensional (3D) modeling of saturated ground-water flow systems, and for cross sectional and 3D modeling of unsaturated zone flow. Solute-transport simulation using SUTRA may be employed to model natural or man-induced chemical-species transport including processes of solute sorption, production, and decay. For example, it may be applied to analyze ground-water contaminant transport problems and aquifer restoration designs. In addition, solute-transport simulation with SUTRA may be used for modeling of variable-density leachate movement, and for cross sectional modeling of saltwater intrusion in aquifers at near-well or regional scales, with either dispersed or relatively sharp transition zones between freshwater and saltwater. SUTRA energy-transport simulation may be employed to model thermal regimes in aquifers, subsurface heat conduction, aquifer thermal-energy storage systems, geothermal reservoirs, thermal pollution of aquifers, and natural hydrogeologic convection systems. Mesh construction, which is quite flexible for arbitrary geometries, employs quadrilateral finite elements in 2D Cartesian or radial-cylindrical coordinate systems, and hexahedral finite elements in 3D systems. 3D meshes are currently restricted to be logically rectangular; in other words, they are similar to deformable finite-difference-style grids. Permeabilities may be anisotropic and may vary in both direction and magnitude throughout the system, as may most other aquifer and fluid properties. Boundary conditions, sources and sinks may be time dependent. A number of input data checks are made to verify the input data set. An option is available for storing intermediate results and restarting a simulation at the intermediate time. Output options include fluid velocities, fluid mass and solute mass or energy budgets, and time-varying observations at points in the system. Both the mathematical basis for SUTRA and the program structure are highly general, and are modularized to allow for straightforward addition of new methods or processes to the simulation. The FORTRAN-90 coding stresses clarity and modularity rather than efficiency, providing easy access for later modifications.

Thermally driven advection for radioxenon transport from an underground nuclear explosion

NASA Astrophysics Data System (ADS)

Sun, Yunwei; Carrigan, Charles R.

2016-05-01

Barometric pumping is a ubiquitous process resulting in migration of gases in the subsurface that has been studied as the primary mechanism for noble gas transport from an underground nuclear explosion (UNE). However, at early times following a UNE, advection driven by explosion residual heat is relevant to noble gas transport. A rigorous measure is needed for demonstrating how, when, and where advection is important. In this paper three physical processes of uncertain magnitude (oscillatory advection, matrix diffusion, and thermally driven advection) are parameterized by using boundary conditions, system properties, and source term strength. Sobol' sensitivity analysis is conducted to evaluate the importance of all physical processes influencing the xenon signals. This study indicates that thermally driven advection plays a more important role in producing xenon signals than oscillatory advection and matrix diffusion at early times following a UNE, and xenon isotopic ratios are observed to have both time and spatial dependence.

STRUCTURE AND FUNCTION OF SUBSURFACE MICROBIAL COMMUNITIES AFFECTING RADIONUCLIDE TRANSPORT AND BIOIMMOBILIZATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joel E. Kostka; Lee Kerkhof; Kuk-Jeong Chin

2011-06-15

The objectives of this project were to: (1) isolate and characterize novel anaerobic prokaryotes from subsurface environments exposed to high levels of mixed contaminants (U(VI), nitrate, sulfate), (2) elucidate the diversity and distribution of metabolically active metal- and nitrate-reducing prokaryotes in subsurface sediments, and (3) determine the biotic and abiotic mechanisms linking electron transport processes (nitrate, Fe(III), and sulfate reduction) to radionuclide reduction and immobilization. Mechanisms of electron transport and U(VI) transformation were examined under near in situ conditions in sediment microcosms and in field investigations at the Oak Ridge Field Research Center (ORFRC), in Oak Ridge, Tennessee, where themore » subsurface is exposed to mixed contamination predominated by uranium and nitrate. A total of 20 publications (16 published or 'in press' and 4 in review), 10 invited talks, and 43 contributed seminars/ meeting presentations were completed during the past four years of the project. PI Kostka served on one proposal review panel each year for the U.S. DOE Office of Science during the four year project period. The PI leveraged funds from the state of Florida to purchase new instrumentation that aided the project. Support was also leveraged by the PI from the Joint Genome Institute in the form of two successful proposals for genome sequencing. Draft genomes are now available for two novel species isolated during our studies and 5 more genomes are in the pipeline. We effectively addressed each of the three project objectives and research highlights are provided. Task I - Isolation and characterization of novel anaerobes: (1) A wide range of pure cultures of metal-reducing bacteria, sulfate-reducing bacteria, and denitrifying bacteria (32 strains) were isolated from subsurface sediments of the Oak Ridge Field Research Center (ORFRC), where the subsurface is exposed to mixed contamination of uranium and nitrate. These isolates which are new to science all show high sequence identity to sequences retrieved from ORFRC subsurface. (2) Based on physiological and phylogenetic characterization, two new species of subsurface bacteria were described: the metal-reducer Geobacter daltonii, and the denitrifier Rhodanobacter denitrificans. (3) Strains isolated from the ORFRC show that Rhodanobacter species are well adapted to the contaminated subsurface. Strains 2APBS1 and 116-2 grow at high salt (3% NaCl), low pH (3.5) and tolerate high concentrations of nitrate (400mM) and nitrite (100mM). Strain 2APBS1 was demonstrated to grow at in situ acidic pHs down to 2.5. (4) R. denitrificans strain 2APBS1 is the first described Rhodanobacter species shown to denitrify. Nitrate is almost entirely converted to N2O, which may account for the large accumulation of N2O in the ORFRC subsurface. (5) G. daltonii, isolated from uranium- and hydrocarbon-contaminated subsurface sediments of the ORFRC, is the first organism from the subsurface clade of the genus Geobacter that is capable of growth on aromatic hydrocarbons. (6) High quality draft genome sequences and a complete eco-physiological description are completed for R. denitrificans strain 2APBS1 and G. daltonii strain FRC-32. (7) Given their demonstrated relevance to DOE remediation efforts and the availability of detailed genotypic/phenotypic characterization, Rhodanobacter denitrificans strain 2APBS1 and Geobacter daltonii strain FRC-32 represent ideal model organisms to provide a predictive understanding of subsurface microbial activity through metabolic modeling. Tasks II and III-Diversity and distribution of active anaerobes and Mechanisms linking electron transport and the fate of radionuclides: (1) Our study showed that members of genus Rhodanobacter and Geobacter are abundant and active in the uranium and nitrate contaminated subsurface. In the contaminant source zone of the Oak Ridge site, Rhodanobacter spp. are the predominant, active organisms detected (comprising 50% to 100% of rRNA detected). (2) We demonstrated for the first time that the function of microbial communities can be quantified in subsurface sediments using messenger RNA assays (molecular proxies) under in situ conditions. (3) Active Geobacteraceae were identified and phylogenetically characterized from the cDNA of messenger RNA extracted from ORFRC subsurface sediment cores. Multiple clone sequences were retrieved from G. uraniireducens, G. daltonii, and G. metallireducens. (4) Results show that Geobacter strain FRC-32 is capable of growth on benzoate, toluene and benzene as the electron donor, thereby providing evidence that this strain is physiologically distinct from other described members of the subsurface Geobacter clade. (5) Fe(III)-reducing bacteria transform structural Fe in clay minerals from their layer edges rather than from their basal surfaces.« less

Use of dissolved and vapor‐phase gases to investigate methanogenic degradation of petroleum hydrocarbon contamination in the subsurface

USGS Publications Warehouse

Amos, Richard T.; Mayer, K. Ulrich; Bekins, Barbara A.; Delin, Geoffrey N.; Williams, Randi L.

2005-01-01

At many sites contaminated with petroleum hydrocarbons, methanogenesis is a significant degradation pathway. Techniques to estimate CH4 production, consumption, and transport processes are needed to understand the geochemical system, provide a complete carbon mass balance, and quantify the hydrocarbon degradation rate. Dissolved and vapor‐phase gas data collected at a petroleum hydrocarbon contaminated site near Bemidji, Minnesota, demonstrate that naturally occurring nonreactive or relatively inert gases such as Ar and N2 can be effectively used to better understand and quantify physical and chemical processes related to methanogenic activity in the subsurface. In the vadose zone, regions of Ar and N2 depletion and enrichment are indicative of methanogenic and methanotrophic zones, and concentration gradients between the regions suggest that reaction‐induced advection can be an important gas transport process. In the saturated zone, dissolved Ar and N2 concentrations are used to quantify degassing driven by methanogenesis and also suggest that attenuation of methane along the flow path, into the downgradient aquifer, is largely controlled by physical processes. Slight but discernable preferential depletion of N2 over Ar, in both the saturated and unsaturated zones near the free‐phase oil, suggests reactivity of N2 and is consistent with other evidence indicating that nitrogen fixation by microbial activity is taking place at this site.

A Cloud Based Framework For Monitoring And Predicting Subsurface System Behaviour

NASA Astrophysics Data System (ADS)

Versteeg, R. J.; Rodzianko, A.; Johnson, D. V.; Soltanian, M. R.; Dwivedi, D.; Dafflon, B.; Tran, A. P.; Versteeg, O. J.

2015-12-01

Subsurface system behavior is driven and controlled by the interplay of physical, chemical, and biological processes which occur at multiple temporal and spatial scales. Capabilities to monitor, understand and predict this behavior in an effective and timely manner are needed for both scientific purposes and for effective subsurface system management. Such capabilities require three elements: Models, Data and an enabling cyberinfrastructure, which allow users to use these models and data in an effective manner. Under a DOE Office of Science funded STTR award Subsurface Insights and LBNL have designed and implemented a cloud based predictive assimilation framework (PAF) which automatically ingests, controls quality and stores heterogeneous physical and chemical subsurface data and processes these data using different inversion and modeling codes to provide information on the current state and evolution of subsurface systems. PAF is implemented as a modular cloud based software application with five components: (1) data acquisition, (2) data management, (3) data assimilation and processing, (4) visualization and result delivery and (5) orchestration. Serverside PAF uses ZF2 (a PHP web application framework) and Python and both open source (ODM2) and in house developed data models. Clientside PAF uses CSS and JS to allow for interactive data visualization and analysis. Client side modularity (which allows for a responsive interface) of the system is achieved by implementing each core capability of PAF (such as data visualization, user configuration and control, electrical geophysical monitoring and email/SMS alerts on data streams) as a SPA (Single Page Application). One of the recent enhancements is the full integration of a number of flow and mass transport and parameter estimation codes (e.g., MODFLOW, MT3DMS, PHT3D, TOUGH, PFLOTRAN) in this framework. This integration allows for autonomous and user controlled modeling of hydrological and geochemical processes. In our presentation we will discuss our software architecture and present the results of using these codes and the overall developed performance of our framework using hydrological, geochemical and geophysical data from the LBNL SFA2 Rifle field site.

Removal of microbial pathogens in a sandy gravel aquifer under forced-gradient subsurface flow conditions

NASA Astrophysics Data System (ADS)

Oudega, Thomas James; Derx, Julia; van Driezum, Inge; Cisneros, Anibal; Sommer, Regina; Kirschner, Alexander; Farnleitner, Andreas; Blaschke, Alfred Paul

2017-04-01

Subsurface media are being used around the world as a means to mitigate microbial contamination, but vary widely in their ability to remove pathogens. To help to provide accurate risk assessments of microbial contamination of groundwaters, and establish safe setback distances between receiving waters and disposal fields, this study aims to use aquifer tracer tests to evaluate the ability of subsurface media to attenuate these pathogens. The novelty of this work is the use of a variety of different tracer substances (e.g. phages, spores, microspheres, conservative tracers) together in field experiments. This will be done by means of injecting these substances under a forced gradient in a sandy gravel aquifer in Lobau, Austria. The extraction of the tracers will be monitored in a pumping well at a distrance of 50m downgradient. This will be able to provide us with insight to the characteristics of microbial transport and how the microorganisms react to the subsurface in the study site. Subsequent numerical modelling of the experiments can tell us more about quantification of subsurface processes such as attachment/detachment, inactivation and die-off of these substances. The first field experiment with conservative tracers (NaCl) has been carried out in December 2016, and subsequent tests are being planned for the next months.

Design and maintenance of subsurface gravel wetlands.

DOT National Transportation Integrated Search

2015-02-01

This report summarizes the University of New Hampshire Stormwater Center (UNHSC) evaluation of : a review of Subsurface Gravel Wetlands design and specifications used by the New Hampshire : Department of Transportation (NHDOT or Department). : Subsur...

Subsurface Environment Sampler for Improved In Situ Characterization of Subsurface Microbial Communities

NASA Astrophysics Data System (ADS)

Barnhart, E. P.; Ruppert, L. F.; Orem, W. H.; McIntosh, J. C.; Cunningham, A. B.; Fields, M. W.; Hiebert, R.; Hyatt, R.

2016-12-01

There is an increasing threat that deep aquifers, an important drinking water resource, may be contaminated by the extraction and transport of fossil fuels. This threat increases the need for improved groundwater monitoring and the ability to predict the extent to which microbial activity may remediate such contamination. The characterization of subsurface microbial communities could provide an ideal biomonitoring tool for the assessment of subsurface contamination due to prokaryotes environmental ubiquity, rapidity of response to environmental perturbation and the important role they play in hydrocarbon degradation and bioremediation. New DNA sequencing technologies provide the opportunity to cost-effectively identify the vast subsurface microbial ecosystem, but use of this new technology is restricted due to issues with sampling. Prior subsurface microbiology studies have relied on core samples that are expensive to obtain hard to collect aseptically and/or ground water samples that do not reflect in situ microbial densities or activities. The development of down-well incubation of sterile sediment with a Diffusive Microbial Sampler (DMS) has emerged as an alternative method to sample subsurface microbial communities that minimizes cost and contamination issues associated with traditional methods. We have designed a Subsurface Environment Sampler with a DMS module that could enable the anaerobic transport of the in situ microbial community from the field for laboratory bioremediation studies. This sampler could provide an inexpensive and standard method for subsurface microbial sampling which would make this tool useful for Federal, State, private and local agencies interested in monitoring contamination or the effectiveness of bioremediation activities in subsurface aquifers.

The impacts of uncertainty and variability in groundwater-driven health risk assessment. (Invited)

NASA Astrophysics Data System (ADS)

Maxwell, R. M.

2010-12-01

Potential human health risk from contaminated groundwater is becoming an important, quantitative measure used in management decisions in a range of applications from Superfund to CO2 sequestration. Quantitatively assessing the potential human health risks from contaminated groundwater is challenging due to the many coupled processes, uncertainty in transport parameters and the variability in individual physiology and behavior. Perspective on human health risk assessment techniques will be presented and a framework used to predict potential, increased human health risk from contaminated groundwater will be discussed. This framework incorporates transport of contaminants through the subsurface from source to receptor and health risks to individuals via household exposure pathways. The subsurface is shown subject to both physical and chemical heterogeneity which affects downstream concentrations at receptors. Cases are presented where hydraulic conductivity can exhibit both uncertainty and spatial variability in addition to situations where hydraulic conductivity is the dominant source of uncertainty in risk assessment. Management implications, such as characterization and remediation will also be discussed.

Microbial Metagenomics Reveals Climate-Relevant Subsurface Biogeochemical Processes.

PubMed

Long, Philip E; Williams, Kenneth H; Hubbard, Susan S; Banfield, Jillian F

2016-08-01

Microorganisms play key roles in terrestrial system processes, including the turnover of natural organic carbon, such as leaf litter and woody debris that accumulate in soils and subsurface sediments. What has emerged from a series of recent DNA sequencing-based studies is recognition of the enormous variety of little known and previously unknown microorganisms that mediate recycling of these vast stores of buried carbon in subsoil compartments of the terrestrial system. More importantly, the genome resolution achieved in these studies has enabled association of specific members of these microbial communities with carbon compound transformations and other linked biogeochemical processes-such as the nitrogen cycle-that can impact the quality of groundwater, surface water, and atmospheric trace gas concentrations. The emerging view also emphasizes the importance of organism interactions through exchange of metabolic byproducts (e.g., within the carbon, nitrogen, and sulfur cycles) and via symbioses since many novel organisms exhibit restricted metabolic capabilities and an associated extremely small cell size. New, genome-resolved information reshapes our view of subsurface microbial communities and provides critical new inputs for advanced reactive transport models. These inputs are needed for accurate prediction of feedbacks in watershed biogeochemical functioning and their influence on the climate via the fluxes of greenhouse gases, CO2, CH4, and N2O. Copyright © 2016 Elsevier Ltd. All rights reserved.

Spectroscopic analyses of soil samples outside Nile Delta of Egypt

NASA Astrophysics Data System (ADS)

Fakhry, Ahmed; Osman, Osama; Ezzat, Hend; Ibrahim, Medhat

2016-11-01

Soil in Egypt, especially around Delta is exposed to various pollutants which are affecting adversely soil fertility and stability. Humic Acids (HA) as a main part of soil organic matter (SOM) represent the heart of the interaction process of inorganic pollutants with soil. Consequently, Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonances (NMR) were used to characterize soil, sediment and extracted HA. Resulting data confirmed that the HA was responsible for transporting inorganic pollutants from surface to subsurface reaching the ground water, which may represent a high risk on public health. The transport process is coming as carboxyl in surface soil changed into metal carboxylate then transferred into the carboxyl in bottom soil.

Evaluating roadway subsurface drainage practices - phase II.

DOT National Transportation Integrated Search

2015-04-01

Well-performing subsurface drainage systems form an important aspect of pavement design by the Iowa Department of : Transportation (DOT). The recently completed Iowa Highway Research Board (IHRB) project TR-643 provided extensive : insights into Iowa...

Development of a geotechnical GIS for subsurface characterization with three dimensional modeling capabilities.

DOT National Transportation Integrated Search

2006-06-01

The New Hampshire Department of Transportation initiated this research to develop a geographical information system (GIS) that : visualizes subsurface conditions three dimensionally by pulling together geotechnical data containing spatial references....

Effect of subsurface drainage on the structural capacity of flexible pavement.

DOT National Transportation Integrated Search

2005-01-01

Following the recommendation of the Virginia Transportation Research Council's Pavement Research Advisory Committee, this project was initiated to determine the effectiveness of including subsurface drainage systems in pavements in Virginia. The rese...

Heat transfer of ascending cryomagma on Europa

NASA Astrophysics Data System (ADS)

Quick, Lynnae C.; Marsh, Bruce D.

2016-06-01

Jupiter's moon Europa has a relatively young surface (60-90 Myr on average), which may be due in part to cryovolcanic processes. Current models for both effusive and explosive cryovolcanism on Europa may be expanded and enhanced by linking the potential for cryovolcanism at the surface to subsurface cryomagmatism. The success of cryomagma transport through Europa's crust depends critically on the rate of ascent relative to the rate of solidification. The final transport distance of cryomagma is thus governed by initial melt volume, ascent rate, overall ascent distance, transport mechanism (i.e., diapirism, diking, or ascent in cylindrical conduits), and melt temperature and composition. The last two factors are especially critical in determining the budget of expendable energy before complete solidification. Here we use these factors as constraints to explore conditions under which cryomagma may arrive at Europa's surface to facilitate cryovolcanism. We find that 1-5 km radius warm ice diapirs ascending from the base of a 10 km thick stagnant lid can reach the shallow subsurface in a partially molten state. Cryomagma transport may be further facilitated if diapirs travel along pre-heated ascent paths. Under certain conditions, cryolava transported from 10 km depths in tabular dikes or pipe-like conduits may reach the surface at temperatures exceeding 250 K. Ascent rates for these geometries may be high enough that isothermal transport is approached. Cryomagmas containing significant amounts of low eutectic impurities can also be delivered to Europa's surface by propagating dikes or pipe-like conduits.

Modelled isotopic fractionation and transient diffusive release of methane from potential subsurface sources on Mars

NASA Astrophysics Data System (ADS)

Stevens, Adam H.; Patel, Manish R.; Lewis, Stephen R.

2017-01-01

We calculate transport timescales of martian methane and investigate the effect of potential release mechanisms into the atmosphere using a numerical model that includes both Fickian and Knudsen diffusion. The incorporation of Knudsen diffusion, which improves on a Fickian description of transport given the low permeability of the martian regolith, means that transport timescales from sources collocated with a putative martian water table are very long, up to several million martian years. Transport timescales also mean that any temporally varying source process, even in the shallow subsurface, would not result in a significant, observable variation in atmospheric methane concentration since changes resulting from small variations in flux would be rapidly obscured by atmospheric transport. This means that a short-lived 'plume' of methane, as detected by Mumma et al. (2009) and Webster et al. (2014), cannot be reconciled with diffusive transport from any reasonable depth and instead must invoke alternative processes such as fracturing or convective plumes. It is shown that transport through the martian regolith will cause a significant change in the isotopic composition of the gas, meaning that methane release from depth will produce an isotopic signature in the atmosphere that could be significantly different than the source composition. The deeper the source, the greater the change, and the change in methane composition in both δ13C and δD approaches -1000 ‰ for sources at a depth greater than around 1 km. This means that signatures of specific sources, in particular the methane produced by biogenesis that is generally depleted in 13CH4 and CH3D, could be obscured. We find that an abiogenic source of methane could therefore display an isotopic fractionation consistent with that expected for biogenic source processes if the source was at sufficient depth. The only unambiguous inference that can be made from measurements of methane isotopes alone is a measured δ13C or δD close to zero or positive implies a shallow, abiogenic source. The effect of transport processes must therefore be carefully considered when attempting to identify the source of any methane observed by future missions, and the severe depletion in heavier isotopologues will have implications for the sensitivity requirements for future missions that aim to measure the isotopic fractionation of methane in the martian atmosphere.

Modeling of isotope fractionation at the catchment scale: How promising is compound specific isotope analysis (CSIA) as a tool for analyzing diffuse pollution by agrochemicals?

NASA Astrophysics Data System (ADS)

Lutz, S. R.; van Meerveld, H. J.; Waterloo, M. J.; Broers, H. P.; van Breukelen, B. M.

2012-04-01

Concentration measurements are indispensable for the assessment of subsurface and surface water pollution by agrochemicals such as pesticides. However, monitoring data is often ambiguous and easily misinterpreted as a decrease in concentration could be caused by transformation, dilution or changes in the application of the pesticide. In this context, compound specific isotope analysis (CSIA) has recently emerged as a complementary monitoring technique. It is based on the measurement of the isotopic composition (e.g. δ13C and δ2H) of the contaminant. Since transformation processes are likely accompanied by isotope fractionation, thus a change in this composition, CSIA offers the opportunity to gain additional knowledge about transport and degradation processes as well as to track pollutants back to their sources. Isotopic techniques have not yet been applied in a comprehensive way in the analysis of catchment-wide organic pollution. We therefore incorporated fractionation processes associated with the fate of pesticides into the numerical flow and solute transport model HydroGeoSphere in order to assess the feasibility of CSIA within the context of catchment monitoring. The model was set up for a hypothetical hillslope transect which drains into a river. Reactive solute transport was driven by two pesticides applications within one year and actual data for rainfall and potential evapotranspiration from a meteorological station in the Netherlands. Degradation of the pesticide was assumed to take place at a higher rate under the prevailing oxic conditions in the topsoil than in deeper, anoxic subsurface layers. In terms of CSIA, these two degradation pathways were associated with different strengths of isotope fractionation for both hydrogen and carbon atoms. By simulating changes in δ13C and δ2H, the share of the oxic and the anoxic reaction on the overall degradation could be assessed. Model results suggest that CSIA is suitable for assessing degradation of diffuse agrochemical pollutants in a relatively simple hydrological system. The simulated shifts in isotopic signals are within a range that could be detected with current isotope analytics. Concentrations in the stream vary significantly only for a short period during and after intense rainfall events. In contrast, CSIA values reveal longer response times such that isotopic shifts are likely to be detected in samples with a coarser temporal resolution. Rainfall events which result in fast lateral subsurface transport from the pollution source to the stream can be separated from those that lead to pollution migration through deeper subsurface zones with much longer travel times. Two-dimensional CSIA highlights an increasing importance of the oxic reaction in the topsoil during the wetter period of the year. In order to examine to which extent CSIA is applicable for more complex hydrological systems, it is projected to simulate isotope fractionation in a 3-dimensional catchment featuring additional processes such as migration from several pollution sources or in-stream degradation.

Hydrologic and biogeochemical controls of river subsurface solutes under agriculturally enhanced ground water flow

USGS Publications Warehouse

Wildman, R.A.; Domagalski, Joseph L.; Hering, J.G.

2009-01-01

The relative influences of hydrologic processes and biogeochemistry on the transport and retention of minor solutes were compared in the riverbed of the lower Merced River (California, USA). The subsurface of this reach receives ground water discharge and surface water infiltration due to an altered hydraulic setting resulting from agricultural irrigation. Filtered ground water samples were collected from 30 drive point locations in March, June, and October 2004. Hydrologic processes, described previously, were verified by observations of bromine concentrations; manganese was used to indicate redox conditions. The separate responses of the minor solutes strontium, barium, uranium, and phosphorus to these influences were examined. Correlation and principal component analyses indicate that hydrologic processes dominate the distribution of trace elements in the ground water. Redox conditions appear to be independent of hydrologic processes and account for most of the remaining data variability. With some variability, major processes are consistent in two sampling transects separated by 100 m. Copyright ?? 2009 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Preface

NASA Astrophysics Data System (ADS)

Faybishenko, Boris; Witherspoon, Paul A.; Gale, John

How to characterize fluid flow, heat, and chemical transport in geologic media remains a central challenge for geoscientists and engineers worldwide. Investigations of fluid flow and transport within rock relate to such fundamental and applied problems as environmental remediation; nonaqueous phase liquid (NAPL) transport; exploitation of oil, gas, and geothermal resources; disposal of spent nuclear fuel; and geotechnical engineering. It is widely acknowledged that fractures in unsaturated-saturated rock can play a major role in solute transport from the land surface to underlying aquifers. It is also evident that general issues concerning flow and transport predictions in subsurface fractured zones can be resolved in a practical manner by integrating investigations into the physical nature of flow in fractures, developing relevant mathematical models and modeling approaches, and collecting site characterization data. Because of the complexity of flow and transport processes in most fractured rock flow problems, it is not yet possible to develop models directly from first principles. One reason for this is the presence of episodic, preferential water seepage and solute transport, which usually proceed more rapidly than expected from volume-averaged and time-averaged models. However, the physics of these processes is still known.

An adaptive Gaussian process-based iterative ensemble smoother for data assimilation

NASA Astrophysics Data System (ADS)

Ju, Lei; Zhang, Jiangjiang; Meng, Long; Wu, Laosheng; Zeng, Lingzao

2018-05-01

Accurate characterization of subsurface hydraulic conductivity is vital for modeling of subsurface flow and transport. The iterative ensemble smoother (IES) has been proposed to estimate the heterogeneous parameter field. As a Monte Carlo-based method, IES requires a relatively large ensemble size to guarantee its performance. To improve the computational efficiency, we propose an adaptive Gaussian process (GP)-based iterative ensemble smoother (GPIES) in this study. At each iteration, the GP surrogate is adaptively refined by adding a few new base points chosen from the updated parameter realizations. Then the sensitivity information between model parameters and measurements is calculated from a large number of realizations generated by the GP surrogate with virtually no computational cost. Since the original model evaluations are only required for base points, whose number is much smaller than the ensemble size, the computational cost is significantly reduced. The applicability of GPIES in estimating heterogeneous conductivity is evaluated by the saturated and unsaturated flow problems, respectively. Without sacrificing estimation accuracy, GPIES achieves about an order of magnitude of speed-up compared with the standard IES. Although subsurface flow problems are considered in this study, the proposed method can be equally applied to other hydrological models.

Transport and Retention of Emulsion Droplets in Sandy Porous Media

NASA Astrophysics Data System (ADS)

Esahani, S. G.; Muller, K.; Chapra, S. C.; Ramsburg, A.

2014-12-01

Emulsions are commonly used as amendments during remediation; yet, the processes controlling the distribution of droplets within the subsurface are not well understood. Given that inadequate spatial and/or temporal delivery of amendments often leads to ineffective treatment, there is a need to better understand emulsion transport. Experiments were conducted to evaluate the transport and retention of emulsion droplets in columns containing Ottawa sands. Breakthrough curves and deposition profiles from these experiments were interrogated using a mathematical model capable of describing attachment, detachment, and straining to begin to elucidate the physical processes controlling delivery. Emulsions were constructed by stabilizing soybean oil droplets within a continuous aqueous phase. Physical properties of the resulting oil-in-water emulsions were favorable for subsurface delivery (nominal properties: 1 g/mL density; 10 cP viscosity; and 1.5 μm droplet d50). Emulsions were introduced to the columns for approximately two pore volumes and followed by an extended flush of background solution. Effluent droplet size distributions did not vary significantly over the course of the experiment and remained similar to those measured for the influent emulsion. Emulsion breakthrough curves exhibited tailing, and deposition profiles were found to be hyper-exponential and unaffected by extended periods of background flow. Depending on emulsion composition and flow characteristics, 10-30% of the injected emulsion was retained on the sand suggesting a non-negligible influence on accessible porosity over the course of the experiment. Experimental results were further interpreted using a droplet transport model that accounts for temporal and spatial variation in porosity due to the retention of the emulsion droplets. At present the model assumes a uniform size distribution of inelastic emulsion droplets which are transported by advection and dispersion, and exchanged with the solid phase through attachment, detachment, and straining processes. Results examine the relative roles of attachment-detachment and straining in reducing the accessible porosity. Evaluation of how the porosity change influences the flow regime for moderately and slightly clogged media is currently under investigation.

Microfluidic Experiments Studying Pore Scale Interactions of Microbes and Geochemistry

NASA Astrophysics Data System (ADS)

Chen, M.; Kocar, B. D.

2016-12-01

Understanding how physical phenomena, chemical reactions, and microbial behavior interact at the pore-scale is crucial to understanding larger scale trends in groundwater chemistry. Recent studies illustrate the utility of microfluidic devices for illuminating pore-scale physical-biogeochemical processes and their control(s) on the cycling of iron, uranium, and other important elements 1-3. These experimental systems are ideal for examining geochemical reactions mediated by microbes, which include processes governed by complex biological phenomenon (e.g. biofilm formation, etc.)4. We present results of microfluidic experiments using a model metal reducing bacteria and varying pore geometries, exploring the limitations of the microorganisms' ability to access tight pore spaces, and examining coupled biogeochemical-physical controls on the cycling of redox sensitive metals. Experimental results will provide an enhanced understanding of coupled physical-biogeochemical processes transpiring at the pore-scale, and will constrain and compliment continuum models used to predict and describe the subsurface cycling of redox-sensitive elements5. 1. Vrionis, H. A. et al. Microbiological and geochemical heterogeneity in an in situ uranium bioremediation field site. Appl. Environ. Microbiol. 71, 6308-6318 (2005). 2. Pearce, C. I. et al. Pore-scale characterization of biogeochemical controls on iron and uranium speciation under flow conditions. Environ. Sci. Technol. 46, 7992-8000 (2012). 3. Zhang, C., Liu, C. & Shi, Z. Micromodel investigation of transport effect on the kinetics of reductive dissolution of hematite. Environ. Sci. Technol. 47, 4131-4139 (2013). 4. Ginn, T. R. et al. Processes in microbial transport in the natural subsurface. Adv. Water Resour. 25, 1017-1042 (2002). 5. Scheibe, T. D. et al. Coupling a genome-scale metabolic model with a reactive transport model to describe in situ uranium bioremediation. Microb. Biotechnol. 2, 274-286 (2009).

Stochastic collocation using Kronrod-Patterson-Hermite quadrature with moderate delay for subsurface flow and transport

NASA Astrophysics Data System (ADS)

Liao, Q.; Tchelepi, H.; Zhang, D.

2015-12-01

Uncertainty quantification aims at characterizing the impact of input parameters on the output responses and plays an important role in many areas including subsurface flow and transport. In this study, a sparse grid collocation approach, which uses a nested Kronrod-Patterson-Hermite quadrature rule with moderate delay for Gaussian random parameters, is proposed to quantify the uncertainty of model solutions. The conventional stochastic collocation method serves as a promising non-intrusive approach and has drawn a great deal of interests. The collocation points are usually chosen to be Gauss-Hermite quadrature nodes, which are naturally unnested. The Kronrod-Patterson-Hermite nodes are shown to be more efficient than the Gauss-Hermite nodes due to nestedness. We propose a Kronrod-Patterson-Hermite rule with moderate delay to further improve the performance. Our study demonstrates the effectiveness of the proposed method for uncertainty quantification through subsurface flow and transport examples.

Geoelectrical monitoring of simulated subsurface leakage to support high-hazard nuclear decommissioning at the Sellafield Site, UK.

PubMed

Kuras, Oliver; Wilkinson, Paul B; Meldrum, Philip I; Oxby, Lucy S; Uhlemann, Sebastian; Chambers, Jonathan E; Binley, Andrew; Graham, James; Smith, Nicholas T; Atherton, Nick

2016-10-01

A full-scale field experiment applying 4D (3D time-lapse) cross-borehole Electrical Resistivity Tomography (ERT) to the monitoring of simulated subsurface leakage was undertaken at a legacy nuclear waste silo at the Sellafield Site, UK. The experiment constituted the first application of geoelectrical monitoring in support of decommissioning work at a UK nuclear licensed site. Images of resistivity changes occurring since a baseline date prior to the simulated leaks revealed likely preferential pathways of silo liquor simulant flow in the vadose zone and upper groundwater system. Geophysical evidence was found to be compatible with historic contamination detected in permeable facies in sediment cores retrieved from the ERT boreholes. Results indicate that laterally discontinuous till units forming localized hydraulic barriers substantially affect flow patterns and contaminant transport in the shallow subsurface at Sellafield. We conclude that only geophysical imaging of the kind presented here has the potential to provide the detailed spatial and temporal information at the (sub-)meter scale needed to reduce the uncertainty in models of subsurface processes at nuclear sites. Copyright © 2016 British Geological Survey, NERC. Published by Elsevier B.V. All rights reserved.

Identifying Hydrologic Flowpaths on Arctic Hillslopes Using Electrical Resistivity and Self Potential

NASA Astrophysics Data System (ADS)

Voytek, E.; Rushlow, C. R.; Godsey, S.; Singha, K.

2015-12-01

Shallow subsurface flow is a dominant process controlling hillslope runoff generation, soil development, and solute reaction and transport. Despite their importance, the location and geometry of flowpaths are difficult to determine. In arctic environments, shallow subsurface flowpaths are limited to a thin zone of seasonal thaw above continuous permafrost, which is traditionally assumed to mimic to surface topography. Here we use a combined approach of electrical resistivity imaging (ERI) and self-potential measurements (SP) to map shallow subsurface flowpaths in and around water tracks, drainage features common to arctic hillslopes. ERI measurements delineate thawed zones in the subsurface that control flowpaths, while SP is sensitive to groundwater flow. We find that areas of low electrical resistivity in the water tracks are deeper than manual thaw depth estimates and variations from surface topography. This finding suggests that traditional techniques significantly underestimate active layer thaw and the extent of the flowpath network on arctic hillslopes. SP measurements identify complex 3-D flowpaths in the thawed zone. Our results lay the groundwork for investigations into the seasonal dynamics, hydrologic connectivity, and climate sensitivity of spatially distributed flowpath networks on arctic hillslopes.

In situ measurement and simulation of nano-magnetite mobility in porous media subject to transient salinity

NASA Astrophysics Data System (ADS)

Becker, Matthew D.; Wang, Yonggang; L. Paulsen, Jeffrey; Song, Yi-Qiao; Abriola, Linda M.; Pennell, Kurt D.

2014-12-01

Nanotechnologies have been proposed for a variety of environmental applications, including subsurface characterization, enhanced oil recovery, and in situ contaminant remediation. For such applications, quantitative predictive models will be of great utility for system design and implementation. Electrolyte chemistry, which can vary substantially within subsurface pore waters, has been shown to strongly influence nanoparticle aggregation and deposition in porous media. Thus, it is essential that mathematical models be capable of tracking changes in electrolyte chemistry and predicting its influence on nanoparticle mobility. In this work, a modified version of a multi-dimensional multispecies transport simulator (SEAWAT) was employed to model nanoparticle transport under transient electrolyte conditions. The modeling effort was supported by experimental measurements of paramagnetic magnetite (Fe3O4) nanoparticle, coated with polyacrylamide-methylpropane sulfonic acid - lauryl acrylate (nMag-PAMPS), mobility in columns packed with 40-50 mesh Ottawa sand. Column effluent analyses and magnetic resonance imaging (MRI) were used to quantify nanoparticle breakthrough and in situ aqueous phase concentrations, respectively. Experimental observations revealed that introduction of de-ionized water into the brine saturated column (80 g L-1 NaCl + 20 g L-1 CaCl2) promoted release and remobilization of deposited nanoparticles along a diagonal front, coincident with the variable density flow field. This behavior was accurately captured by the simulation results, which indicated that a two-site deposition-release model provided the best fit to experimental observations, suggesting that heterogeneous nanoparticle-surface interactions governed nanoparticle attachment. These findings illustrate the importance of accounting for both physical and chemical processes associated with changes in electrolyte chemistry when predicting nanoparticle transport behavior in subsurface formations.Nanotechnologies have been proposed for a variety of environmental applications, including subsurface characterization, enhanced oil recovery, and in situ contaminant remediation. For such applications, quantitative predictive models will be of great utility for system design and implementation. Electrolyte chemistry, which can vary substantially within subsurface pore waters, has been shown to strongly influence nanoparticle aggregation and deposition in porous media. Thus, it is essential that mathematical models be capable of tracking changes in electrolyte chemistry and predicting its influence on nanoparticle mobility. In this work, a modified version of a multi-dimensional multispecies transport simulator (SEAWAT) was employed to model nanoparticle transport under transient electrolyte conditions. The modeling effort was supported by experimental measurements of paramagnetic magnetite (Fe3O4) nanoparticle, coated with polyacrylamide-methylpropane sulfonic acid - lauryl acrylate (nMag-PAMPS), mobility in columns packed with 40-50 mesh Ottawa sand. Column effluent analyses and magnetic resonance imaging (MRI) were used to quantify nanoparticle breakthrough and in situ aqueous phase concentrations, respectively. Experimental observations revealed that introduction of de-ionized water into the brine saturated column (80 g L-1 NaCl + 20 g L-1 CaCl2) promoted release and remobilization of deposited nanoparticles along a diagonal front, coincident with the variable density flow field. This behavior was accurately captured by the simulation results, which indicated that a two-site deposition-release model provided the best fit to experimental observations, suggesting that heterogeneous nanoparticle-surface interactions governed nanoparticle attachment. These findings illustrate the importance of accounting for both physical and chemical processes associated with changes in electrolyte chemistry when predicting nanoparticle transport behavior in subsurface formations. Electronic supplementary information (ESI) available: A schematic diagram of the nMag-MRI experimental systems, description of the mathematical modeling domain, further information regarding calibration of R2 to nMag concentration in sand, comparison of one- and two-site simulations of phases 1 and 2, DLVO interaction energy profiles for the system, and a time lapse movie of the best fit two-site model simulation of the nMag experimental data. See DOI: 10.1039/c4nr05088f

Soils as sinks or sources for diffuse pollution of the water cycle

NASA Astrophysics Data System (ADS)

Grathwohl, Peter

2010-05-01

Numerous chemical compounds have been released into the environment by human activities and can nowadays be found everywhere, i.e. in the compartments water, soil, and air, at the poles and in high mountains. Examples for a global distribution of toxic compounds are the persistent organic pollutants (PCB, dioxins, PAH, fluorinated surfactants and flame retardants, etc.: "the Stockholm dirty dozen") but also mercury and other metals. Many of these compounds reached a global distribution via the atmo¬sphere; others have been and are still directly applied to top soils at the large scale by agriculture or are released into groundwater at landfill sites or by discharge of treated or untreated waste waters. Sooner or later such compounds end up in the water cycle - often via an intermediate storage in soils. Pollutants in soils are leached by seepage waters, transferred to ground¬water, and transported to rivers via groundwater flow. Adsorbed compounds may be transported from soils into surface waters by erosion processes and will end up in the sediments. Diffuse pollution of the subsurface environment not only reflects the history of the economic development of the modern society but it is still ongoing - e.g. the number of organic pollutants released into the environment is increasing even though the con¬centrations may decrease compared to the past. Evidence shows that many compounds are persistent in the subsurface environment at large time scales (up to centuries). Thus polluted soils already are or may become a future source for pollution of adjacent compartments such as the atmosphere and groundwater. A profound understanding on how diffuse pollutants are stored and processed in the subsurface environment is crucial to assess their long term fate and transport at large scales. Thus integrated studies e.g. at the catchment scale and models are needed which couple not only the relevant compartments (soil - atmosphere - groundwater/surface waters) but also flow and reactive transport. Field observations must allow long-term monitoring (e.g. in hydrological observatories, TERENO etc.), new cross-compartment monitoring strategies need to be applied, and massive parallel numerical codes for prediction of reactive transport of potential water pollutants at catchment scale have to be developed. This is also a prerequisite to assess the impact of climate change as well as land use change on future surface and groundwater quality.

Europa's shallow subsurface: lakes, layers and life? (Invited)

NASA Astrophysics Data System (ADS)

Schmidt, B. E.; Soderlund, K. M.; Gooch, B. T.; Blankenship, D. D.

2013-12-01

With an icy exterior covering a global ocean, Europa has long been a target of interest in the search for life beyond Earth. A critical question related to the habitability of this icy world is: how does the ice shell recycle? Recent detection of shallow subsurface water lenses or "lakes" joins the evidence that implies Europa is currently active, recycling its ice shell. This new perspective has important astrobiological implications. At a surface age of 40-90 Myr, and about 50% covered by chaos terrain, Europa's resurfacing rate is likely to be very high if water does play a significant role in their formation. Because of the vigor of overturn implied if chaos does form by the collapse of ice above subsurface lenses, it is likely that surface and subsurface materials are well-mixed within the largest and deepest lenses, providing a mechanism for bringing oxidants and other surface contaminants to the deeper ice shell where it can reach the ocean by convective or compositional effects. The timescales over which large lenses refreeze (a few hundred thousand years) are large compared to the timescales for vertical transport (a few tens of thousands of years), while the timescales for smaller lenses are comparable to or shorter than convective timescales but involving smaller impurity loads than for larger more well-mixed sources. Melt lenses are intriguing potential habitats, particularly the larger features. Moreover, their formation likely requires the existence of impurities within the upper ice shell that may be sources of energy for microorganisms. Geomorphic evidence also exists for brine percolation that can disperse fluids both vertically and horizontally through pores and fractures. This process, observed in terrestrial ice shelves, may preserve liquid water within the ice matrix over many kilometers from the source. Horizontal transport of material may produce interconnectivity between distinct regions of Europa, providing a pathway for transferring nutrients and biomass, thus preserving habitable conditions within the ice over a longer duration. From this point of view, we evaluate the habitability of Europa's ice and ocean in light of active processes, including the lifetime of liquid reservoirs, vertical and horizontal material transport, and the resurfacing rate of the body that may be responsible both for reenergizing and destroying shallow habitats.

Viral Tracer Studies Indicate Contamination of Marine Waters by Sewage Disposal Practices in Key Largo, Florida

PubMed Central

Paul, J. H.; Rose, J. B.; Brown, J.; Shinn, E. A.; Miller, S.; Farrah, S. R.

1995-01-01

Domestic wastewater disposal practices in the Florida Keys are primarily limited to on-site disposal systems such as septic tanks, injection wells, and illegal cesspits. Poorly treated sewage is thus released into the highly porous subsurface Key Largo limestone matrix. To investigate the fate and transport of sewage in the subsurface environment and the potential for contamination of marine surface waters, we employed bacteriophages as tracers in a domestic septic system and a simulated injection well in Key Largo, Florida. Transport of bacteriophage (Phi)HSIC-1 from the septic tank to adjacent surface canal waters and outstanding marine waters occurred in as little as 11 and 23 h, respectively. Transport of the Salmonella phage PRD1 from the simulated injection well to a canal adjacent to the injection site occurred in 11.2 h. Estimated rates of migration of viral tracers ranged from 0.57 to 24.2 m/h, over 500-fold greater than flow rates measured previously by subsurface flow meters in similar environments. These results suggest that current on-site disposal practices can lead to contamination of the subsurface and surface marine waters in the Keys. PMID:16535046

Viral tracer studies indicate contamination of marine waters by sewage disposal practices in key largo, Florida.

PubMed

Paul, J H; Rose, J B; Brown, J; Shinn, E A; Miller, S; Farrah, S R

1995-06-01

Domestic wastewater disposal practices in the Florida Keys are primarily limited to on-site disposal systems such as septic tanks, injection wells, and illegal cesspits. Poorly treated sewage is thus released into the highly porous subsurface Key Largo limestone matrix. To investigate the fate and transport of sewage in the subsurface environment and the potential for contamination of marine surface waters, we employed bacteriophages as tracers in a domestic septic system and a simulated injection well in Key Largo, Florida. Transport of bacteriophage (Phi)HSIC-1 from the septic tank to adjacent surface canal waters and outstanding marine waters occurred in as little as 11 and 23 h, respectively. Transport of the Salmonella phage PRD1 from the simulated injection well to a canal adjacent to the injection site occurred in 11.2 h. Estimated rates of migration of viral tracers ranged from 0.57 to 24.2 m/h, over 500-fold greater than flow rates measured previously by subsurface flow meters in similar environments. These results suggest that current on-site disposal practices can lead to contamination of the subsurface and surface marine waters in the Keys.

Investigating ebullition in a sand column using dissolved gas analysis and reactive transport modeling

USGS Publications Warehouse

Amos, Richard T.; Mayer, K. Ulrich

2006-01-01

Ebullition of gas bubbles through saturated sediments can enhance the migration of gases through the subsurface, affect the rate of biogeochemical processes, and potentially enhance the emission of important greenhouse gases to the atmosphere. To better understand the parameters controlling ebullition, methanogenic conditions were produced in a column experiment and ebullition through the column was monitored and quantified through dissolved gas analysis and reactive transport modeling. Dissolved gas analysis showed rapid transport of CH4 vertically through the column at rates several times faster than the bromide tracer and the more soluble gas CO2, indicating that ebullition was the main transport mechanism for CH4. An empirically derived formulation describing ebullition was integrated into the reactive transport code MIN3P allowing this process to be investigated on the REV scale in a complex geochemical framework. The simulations provided insights into the parameters controlling ebullition and show that, over the duration of the experiment, 36% of the CH4 and 19% of the CO2 produced were transported to the top of the column through ebullition.

Numerical simulation of seasonal heat storage in a contaminated shallow aquifer - Temperature influence on flow, transport and reaction processes

NASA Astrophysics Data System (ADS)

Popp, Steffi; Beyer, Christof; Dahmke, Andreas; Bauer, Sebastian

2015-04-01

The energy market in Germany currently faces a rapid transition from nuclear power and fossil fuels towards an increased production of energy from renewable resources like wind or solar power. In this context, seasonal heat storage in the shallow subsurface is becoming more and more important, particularly in urban regions with high population densities and thus high energy and heat demand. Besides the effects of increased or decreased groundwater and sediment temperatures on local and large-scale groundwater flow, transport, geochemistry and microbiology, an influence on subsurface contaminations, which may be present in the urban surbsurface, can be expected. Currently, concerns about negative impacts of temperature changes on groundwater quality are the main barrier for the approval of heat storage at or close to contaminated sites. The possible impacts of heat storage on subsurface contamination, however, have not been investigated in detail yet. Therefore, this work investigates the effects of a shallow seasonal heat storage on subsurface groundwater flow, transport and reaction processes in the presence of an organic contamination using numerical scenario simulations. A shallow groundwater aquifer is assumed, which consists of Pleistoscene sandy sediments typical for Northern Germany. The seasonal heat storage in these scenarios is performed through arrays of borehole heat exchangers (BHE), where different setups with 6 and 72 BHE, and temperatures during storage between 2°C and 70°C are analyzed. The developing heat plume in the aquifer interacts with a residual phase of a trichloroethene (TCE) contamination. The plume of dissolved TCE emitted from this source zone is degraded by reductive dechlorination through microbes present in the aquifer, which degrade TCE under anaerobic redox conditions to the degradation products dichloroethene, vinyl chloride and ethene. The temperature dependence of the microbial degradation activity of each degradation step is taken into account for the numerical simulations. Hence, the simulations are performed with the code OpenGeoSys, which is especially suited for simulating coupled thermal, hydraulic and geochemical processes. The scenario simulations show an increase in the source zone emission of TCE at higher temperatures, which is primarily due to the focusing of the groundwater flow in the area of higher temperatures within the source zone and to a lesser part to an increase in TCE solubility. On the other hand, a widening of the contaminant plume and enlargement of the area for TCE biodegradation is induced, which leads to an increase in biodegradation of the chlorinated hydrocarbons. In combination almost no change in the overall ratio of degraded to emitted TCE is found, which shows that the seasonal heat storage is not negatively influencing the present TCE contamination under these assumptions. The results of this work serve to support the risk assessment for the interaction between heat storage and contaminations in the shallow subsurface and show positive interactions as well as possible conflicts.

Ebullition, Plant-Mediated Transport, and Subsurface Horizontal Water Flow Dominate Methane Transport in an Arctic Sphagnum Bog

NASA Astrophysics Data System (ADS)

Wehr, R. A.; McCalley, C. K.; Logan, T. A.; Chanton, J.; Crill, P. M.; Rich, V. I.; Saleska, S. R.

2017-12-01

Emission of the greenhouse gas methane from wetlands is of prime concern in the prediction of climate change - especially emission associated with thawing permafrost, which may drive a positive feedback loop of emission and warming. In addition to the biochemistry of methane production and consumption, wetland methane emission depends critically on the transport mechanisms by which methane moves through and out of the ecosystem. We therefore developed a model of methane biochemistry and transport for a sphagnum bog representing an intermediate permafrost thaw stage in Stordalen Mire, Sweden. In order to simultaneously reproduce measured profiles of both the concentrations and isotopic compositions of both methane and carbon dioxide in the peat pore water (Fig. 1) - as well as the surface methane emission - it was necessary for the model to include ebullition, plant-mediated transport via aerenchyma, and subsurface horizontal water flow. Diffusion of gas through the pore water was relatively unimportant. As a result, 90% of the produced methane escaped the wetland rather than being consumed by methanotrophic organisms in the near-surface pore water. Our model provides a comprehensive picture of methane emission from this bog site by quantifying the vertical profiles of: acetoclastic methanogenesis, hydrogenotrophic methanogenesis, methane oxidation, aerobic respiration, ebullition, plant-mediated transport, subsurface horizontal water flow, and diffusion.

STUDIES OF INTERFACIAL REACTIONS BETWEEN ARSENIC AND MINERALS AND ITS SIGNIFICANCE TO SITE CHARACTERIZATION

EPA Science Inventory

Natural attenuation remediation is based on the intrinsic attenuation capacities of the subsurface. Geochemistry of the subsurface controls the fate, transport, transformation, and bioavailability of contaminants. This paper demonstrates that interfacial reactions (e.g., adsorp...

Sonar imaging of flooded subsurface voids phase I : proof of concept.

DOT National Transportation Integrated Search

2011-04-15

Damage to Ohio highways due to subsidence or collapse of subsurface voids is a serious problem : for the Office of Geotechnical Engineering (OGE) at the Ohio Department of Transportation : (ODOT). These voids have often resulted from past underground...

Robust Representation of Integrated Surface-subsurface Hydrology at Watershed Scales

NASA Astrophysics Data System (ADS)

Painter, S. L.; Tang, G.; Collier, N.; Jan, A.; Karra, S.

2015-12-01

A representation of integrated surface-subsurface hydrology is the central component to process-rich watershed models that are emerging as alternatives to traditional reduced complexity models. These physically based systems are important for assessing potential impacts of climate change and human activities on groundwater-dependent ecosystems and water supply and quality. Integrated surface-subsurface models typically couple three-dimensional solutions for variably saturated flow in the subsurface with the kinematic- or diffusion-wave equation for surface flows. The computational scheme for coupling the surface and subsurface systems is key to the robustness, computational performance, and ease-of-implementation of the integrated system. A new, robust approach for coupling the subsurface and surface systems is developed from the assumption that the vertical gradient in head is negligible at the surface. This tight-coupling assumption allows the surface flow system to be incorporated directly into the subsurface system; effects of surface flow and surface water accumulation are represented as modifications to the subsurface flow and accumulation terms but are not triggered until the subsurface pressure reaches a threshold value corresponding to the appearance of water on the surface. The new approach has been implemented in the highly parallel PFLOTRAN (www.pflotran.org) code. Several synthetic examples and three-dimensional examples from the Walker Branch Watershed in Oak Ridge TN demonstrate the utility and robustness of the new approach using unstructured computational meshes. Representation of solute transport in the new approach is also discussed. Notice: This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC0500OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the United States Government purposes.

An analysis of a mixed convection associated with thermal heating in contaminated porous media.

PubMed

Krol, Magdalena M; Johnson, Richard L; Sleep, Brent E

2014-11-15

The occurrence of subsurface buoyant flow during thermal remediation was investigated using a two dimensional electro-thermal model (ETM). The model incorporated electrical current flow associated with electrical resistance heating, energy and mass transport, and density dependent water flow. The model was used to examine the effects of heating on sixteen subsurface scenarios with different applied groundwater fluxes and soil permeabilities. The results were analyzed in terms of the ratio of Rayleigh to thermal Peclet numbers (the buoyancy ratio). It was found that when the buoyancy number was greater than unity and the soil permeability greater than 10(-12) m(2), buoyant flow and contaminant transport were significant. The effects of low permeability layers and electrode placement on heat and mass transport were also investigated. Heating under a clay layer led to flow stagnation zones resulting in the accumulation of contaminant mass and transport into the low permeability layer. The results of this study can be used to develop dimensionless number-based guidelines for site management during subsurface thermal activities. Copyright © 2014 Elsevier B.V. All rights reserved.

Subsurface agricultural irrigation drainage: the need for regulation.

PubMed

Lemly, A D

1993-04-01

Subsurface drainage resulting from irrigated agriculture is a toxic threat to fish and wildlife resources throughout the western United States. Studies by the U.S. Department of the Interior show that migratory waterfowl have been poisoned by drainwater contaminants on at least six national wildlife refuges. Allowing this poisoning to continue is a violation of the Migratory Bird Treaty Act under U.S. Federal law. Critical wetlands and waterfowl populations are threatened in both the Pacific and Central flyways. The public is also at risk and health warnings have been issued in some locations. Subsurface irrigation drainage is a complex effluent containing toxic concentrations of trace elements, salts, and nitrogenous compounds. Some of the contaminants are classified by the U.S. Environmental Protection Agency (EPA) as priority pollutants and they can be present in concentrations that exceed EPA's criteria for toxic waste. The on-farm drainage systems used to collect and transport this wastewater provide point-source identification as well as a mechanism for toxics control through the National Pollutant Discharge Elimination System (NPDES) permit process. A four-step approach is presented for dealing with irrigation drainage in an environmentally sound manner. This regulatory strategy is very similar to those commonly used for industrial discharges and includes site evaluation, contaminant reduction through NPDES, and compliance monitoring. The EPA must recognize subsurface irrigation drainage as a specific class of pollution subject to regulation under the NPDES process. Active involvement by EPA is necessary to ensure that adequate controls on this wastewater are implemented.

Physically-Based Models for the Reflection, Transmission and Subsurface Scattering of Light by Smooth and Rough Surfaces, with Applications to Realistic Image Synthesis

NASA Astrophysics Data System (ADS)

He, Xiao Dong

This thesis studies light scattering processes off rough surfaces. Analytic models for reflection, transmission and subsurface scattering of light are developed. The results are applicable to realistic image generation in computer graphics. The investigation focuses on the basic issue of how light is scattered locally by general surfaces which are neither diffuse nor specular; Physical optics is employed to account for diffraction and interference which play a crucial role in the scattering of light for most surfaces. The thesis presents: (1) A new reflectance model; (2) A new transmittance model; (3) A new subsurface scattering model. All of these models are physically-based, depend on only physical parameters, apply to a wide range of materials and surface finishes and more importantly, provide a smooth transition from diffuse-like to specular reflection as the wavelength and incidence angle are increased or the surface roughness is decreased. The reflectance and transmittance models are based on the Kirchhoff Theory and the subsurface scattering model is based on Energy Transport Theory. They are valid only for surfaces with shallow slopes. The thesis shows that predicted reflectance distributions given by the reflectance model compare favorably with experiment. The thesis also investigates and implements fast ways of computing the reflectance and transmittance models. Furthermore, the thesis demonstrates that a high level of realistic image generation can be achieved due to the physically -correct treatment of the scattering processes by the reflectance model.

Dynamics of Fluids and Transport in Fractured Rock

NASA Astrophysics Data System (ADS)

Faybishenko, Boris; Witherspoon, Paul A.; Gale, John

How to characterize fluid flow, heat, and chemical transport in geologic media remains a central challenge for geo-scientists and engineers worldwide. Investigations of fluid flow and transport within rock relate to such fundamental and applied problems as environmental remediation; nonaqueous phase liquid (NAPL) transport; exploitation of oil, gas, and geothermal resources; disposal of spent nuclear fuel; and geotechnical engineering. It is widely acknowledged that fractures in unsaturated-saturated rock can play a major role in solute transport from the land surface to underlying aquifers. It is also evident that general issues concerning flow and transport predictions in subsurface fractured zones can be resolved in a practical manner by integrating investigations into the physical nature of flow in fractures, developing relevant mathematical models and modeling approaches, and collecting site characterization data. Because of the complexity of flow and transport processes in most fractured rock flow problems, it is not yet possible to develop models directly from first principles. One reason for this is the presence of episodic, preferential water seepage and solute transport, which usually proceed more rapidly than expected from volume-averaged and time-averaged models. However, the physics of these processes is still known.

Sonar imaging of flooded subsurface voids phase I : proof of concept : executive summary report.

DOT National Transportation Integrated Search

2011-04-15

Damage to Ohio highways due to subsidence : or collapse of subsurface voids is a serious : problem for the Ohio Department of : Transportation (ODOT). These voids have : often resulted from past underground mining : activities for coal, clay, limesto...

Environmental Remediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

2017-04-11

At Pacific Northwest National Laboratory, we are a leader in subsurface science and remediation. We use our expertise in these areas to characterize subsurface contaminants and assess contaminant transport. We're also using our capabilities to restore the Hanford Site in southeastern Washington State to a safe, clean environment.

PHT3D-UZF: A reactive transport model for variably-saturated porous media

USGS Publications Warehouse

Wu, Ming Zhi; Post, Vincent E. A.; Salmon, S. Ursula; Morway, Eric D.; Prommer, H.

2016-01-01

A modified version of the MODFLOW/MT3DMS-based reactive transport model PHT3D was developed to extend current reactive transport capabilities to the variably-saturated component of the subsurface system and incorporate diffusive reactive transport of gaseous species. Referred to as PHT3D-UZF, this code incorporates flux terms calculated by MODFLOW's unsaturated-zone flow (UZF1) package. A volume-averaged approach similar to the method used in UZF-MT3DMS was adopted. The PHREEQC-based computation of chemical processes within PHT3D-UZF in combination with the analytical solution method of UZF1 allows for comprehensive reactive transport investigations (i.e., biogeochemical transformations) that jointly involve saturated and unsaturated zone processes. Intended for regional-scale applications, UZF1 simulates downward-only flux within the unsaturated zone. The model was tested by comparing simulation results with those of existing numerical models. The comparison was performed for several benchmark problems that cover a range of important hydrological and reactive transport processes. A 2D simulation scenario was defined to illustrate the geochemical evolution following dewatering in a sandy acid sulfate soil environment. Other potential applications include the simulation of biogeochemical processes in variably-saturated systems that track the transport and fate of agricultural pollutants, nutrients, natural and xenobiotic organic compounds and micropollutants such as pharmaceuticals, as well as the evolution of isotope patterns.

Biogeochemical Role of Subsurface Coherent Eddies in the Ocean: Tracer Cannonballs, Hypoxic Storms, and Microbial Stewpots?

NASA Astrophysics Data System (ADS)

Frenger, Ivy; Bianchi, Daniele; Stührenberg, Carolin; Oschlies, Andreas; Dunne, John; Deutsch, Curtis; Galbraith, Eric; Schütte, Florian

2018-02-01

Subsurface eddies are known features of ocean circulation, but the sparsity of observations prevents an assessment of their importance for biogeochemistry. Here we use a global eddying (0.1°) ocean-biogeochemical model to carry out a census of subsurface coherent eddies originating from eastern boundary upwelling systems (EBUS) and quantify their biogeochemical effects as they propagate westward into the subtropical gyres. While most eddies exist for a few months, moving over distances of hundreds of kilometers, a small fraction (<5%) of long-lived eddies propagates over distances greater than 1,000 km, carrying the oxygen-poor and nutrient-rich signature of EBUS into the gyre interiors. In the Pacific, transport by subsurface coherent eddies accounts for roughly 10% of the offshore transport of oxygen and nutrients in pycnocline waters. This "leakage" of subsurface waters can be a significant fraction of the transport by nutrient-rich poleward undercurrents and may contribute to the well-known reduction of productivity by eddies in EBUS. Furthermore, at the density layer of their cores, eddies decrease climatological oxygen locally by close to 10%, thereby expanding oxygen minimum zones. Finally, eddies represent low-oxygen extreme events in otherwise oxygenated waters, increasing the area of hypoxic waters by several percent and producing dramatic short-term changes that may play an important ecological role. Capturing these nonlocal effects in global climate models, which typically include noneddying oceans, would require dedicated parameterizations.

Actinobacterial diversity across a marine transgression in the deep subsurface off Shimokita Peninsula, Japan

NASA Astrophysics Data System (ADS)

Harrison, B. K.; Bailey, J. V.

2013-12-01

Sediment horizons represent a significant - but not permanent - barrier to microbial transport. Cells commonly attach to mineral surfaces in unconsolidated sediments. However, by taxis, growth, or passive migration under advecting fluids, some portion of the microbial community may transgress sedimentary boundaries. Few studies have attempted to constrain such transport of community signatures in the marine subsurface and its potential impact on biogeography. Integrated Ocean Drilling Program (IODP) Expedition 337 off the Shimokita Peninsula recovered sediments over a greater than 1km interval representing a gradual decrease of terrestrial influence, from tidal to continental shelf depositional settings. This sequence represents a key opportunity to link subsurface microbial communities to lithological variability and investigate the permanence of community signatures characteristic of distinct depositional regimes. The phylogenetic connectivity between marine and terrestrially-influenced deposits may demonstrate to what degree sediments offer a substantial barrier to cell transport in the subsurface. Previous work has demonstrated that the Actinobacterial phylum is broadly distributed in marine sediments (Maldonado et al., 2005), present and active in the deep subsurface (Orsi et al., 2013), and that marine and terrestrial lineages may potentially be distinguished by 16S rRNA gene sequencing (e.g. Prieto-Davó et al., 2013). We report on Actinobacteria-specific 16S rRNA gene diversity recovered between 1370 and 2642 mbsf with high-throughput sequencing using the Illumina MiSeq platform, as well as selective assembly and analysis of environmental clone libraries.

Impact of transient stream flow on water exchange and reactions in the hyporheic zone of an in-stream gravel bar

NASA Astrophysics Data System (ADS)

Trauth, Nico; Schmidt, Christian; Fleckenstein, Jan H.

2015-04-01

Groundwater-surface water exchange is an important process that can facilitate the degradation of critical substances like nitrogen-species and contaminants, supporting a healthy status of the aquatic ecosystem. In our study, we simulate water exchange, solute transport and reactions within a natural in-stream gravel bar using a coupled surface and subsurface numerical model. Stream water flow is simulated by computational fluid dynamics software that provides hydraulic head distributions at the streambed, which are used as an upper boundary condition for a groundwater model. In the groundwater model water exchange, solute transport, aerobic respiration and denitrification in the subsurface are simulated. Ambient groundwater flow is introduced by lateral upstream and downstream hydraulic head boundaries that generate neutral, losing or gaining stream conditions. Stream water transports dissolved oxygen, organic carbon (as the dominant electron donor) and nitrate into the subsurface, whereas an additional nitrate source exists in the ambient groundwater. Scenarios of stream flow events varying in duration and stream stage are simulated and compared with steady state scenarios with respect to water fluxes, residence times and the solute turn-over rates. Results show, that water exchange and solute turn-over rates highly depend on the interplay between event characteristics and ambient groundwater levels. For scenarios, where the stream flow event shifts the hydraulic system to a net-neutral hydraulic gradient between the average stream stage and the ambient groundwater level (minimal exchange between ground- and surface water), solute consumption is higher, compared to the steady losing or gaining case. In contrast, events that induce strong losing conditions lead to a lower potential of solute consumption.

Pollen from accurately dated speleothems supports alpine glacier low-stands during the early Holocene

NASA Astrophysics Data System (ADS)

Festi, Daniela; Hoffmann, Dirk L.; Luetscher, Marc

2016-07-01

Deciphering pollen assemblages from alpine speleothems holds potential to provide unique information about past vegetation in rapidly changing environments. Here, we reconstruct subsurface aerosol transport at Milchbach cave (Switzerland, 1840 m asl) based on the pollen content of two Holocene stalagmites. We demonstrate that pollen is chiefly associated with bacterially mediated calcite fabrics, typical of a well-ventilated cave system. In contrast, pollen is absent from columnar calcite fabrics confirming that hydrological transport is not a significant process for the incorporation of pollen into speleothems at Milchbach cave. Our results support significant changes in the subsurface ventilation regime, which can be associated with the waxing and waning of Upper Grindelwald glacier. Pollen assemblages obtained from six carbonate sub-samples attest the presence of a mixed deciduous forest in the Grindelwald valley during the early and middle Holocene, in agreement with coeval regional pollen records. This study demonstrates that even small amounts of calcite (0.3-2.8 cm3) are capable of delivering pollen spectra representative of the original vegetation if sufficiently elevated deposition fluxes are provided.

MODELING MULTIPHASE ORGANIC CHEMICAL TRANSPORT IN SOILS AND GROUND WATER

EPA Science Inventory

Subsurface contamination due to immiscible organic liquids is a widespread problem which poses a serious threat to ground-water resources. n order to understand the movement of such materials in the subsurface, a mathematical model was developed for multiphase flow and multicompo...

Tillage impact on herbicide loss by surface runoff and lateral subsurface flow

USDA-ARS?s Scientific Manuscript database

There is worldwide interest in conservation tillage practices because they can reduce surface runoff, agrichemical, and sediment loss from farm fields. Since these practices typically increase infiltration, their use may increase subsurface transport of water-soluble contaminants. Thus, to assess lo...

Sediment transport simulation in an armoured stream

USGS Publications Warehouse

Milhous, Robert T.; Bradley, Jeffrey B.; Loeffler, Cindy L.

1986-01-01

Improved methods of calculating bed material stability and transport must be developed for a gravel bed stream having an armoured surface in order to use the HEC-6 model to examine channel change. Good possibilities exist for use of a two layer model based on the Schoklitsch and the Einstein-Brown transport equations. In Einstein-Brown the D35 of the armour is used for stabilities and the D50 of the bed (sub-surface) is used for transport. Data on the armour and sub-surface size distribution needs to be obtained as part of a bed material study in a gravel bed river; a "shovel" sample is not adequate. The Meyer-Peter, Muller equation should not be applied to a gravel bed stream with an armoured surface to estimate the initiation of transport or for calculation of transport at low effective bed shear stress.

Gas Transport and Detection Following Underground Nuclear Explosions

NASA Astrophysics Data System (ADS)

Carrigan, C. R.; Sun, Y.; Wagoner, J. L.; Zucca, J. J.

2011-12-01

Some extremely rare radioactive noble gases are by-products of underground nuclear explosions, and the detection of significant levels of these gases (e.g., Xe-133 and Ar-37) at the surface is a very strong indicator of the occurrence of an underground nuclear event. Because of their uniqueness, such noble gas signatures can be confirmatory of the nuclear nature of an event while signatures from other important detection methods, such as anomalous seismicity, are generally not. As a result, noble gas detection at a suspected underground nuclear test site is considered to be the most important technique available to inspectors operating under the On-Site-Inspection protocol of the Comprehensive Nuclear Test Ban Treaty. A one-kiloton chemical underground explosion, the Non-Proliferation Experiment (NPE), was carried out at the Nevada Test Site in 1993 and represented the first On-Site-Inspection oriented test of subsurface gas transport with subsequent detection at the surface using soil gas sampling methods. A major conclusion of the experiment was that noble gases from underground nuclear tests have a good possibility of being detected even if the test is well contained. From this experiment and from computer simulations, we have also learned significant lessons about the modes of gas transport to the surface and the importance of careful subsurface sampling to optimize the detected noble gas signature. Understanding transport and sampling processes for a very wide range of geologic and testing scenarios presents significant challenges that we are currently addressing using sensitivity studies, which we attempt to verify using experiments such as the NPE and a new subsurface gas migration experiment that is now being undertaken at the National Center for Nuclear Security. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Geochemical and Hydrologic Factors Controlling Subsurface Transport of Poly- and Perfluoroalkyl Substances, Cape Cod, Massachusetts.

PubMed

Weber, Andrea K; Barber, Larry B; LeBlanc, Denis R; Sunderland, Elsie M; Vecitis, Chad D

2017-04-18

Growing evidence that certain poly- and perfluoroalkyl substances (PFASs) are associated with negative human health effects prompted the U.S. Environmental Protection Agency to issue lifetime drinking water health advisories for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in 2016. Given that groundwater is a major source of drinking water, the main objective of this work was to investigate geochemical and hydrological processes governing the subsurface transport of PFASs at a former fire training area (FTA) on Cape Cod, Massachusetts, where PFAS-containing aqueous film-forming foams were used historically. A total of 148 groundwater samples and 4 sediment cores were collected along a 1200-m-long downgradient transect originating near the FTA and analyzed for PFAS content. The results indicate that unsaturated zones at the FTA and at hydraulically downgradient former domestic wastewater effluent infiltration beds both act as continuous PFAS sources to the groundwater despite 18 and 20 years of inactivity, respectively. Historically different PFAS sources are evident from contrasting PFAS composition near the water table below the FTA and wastewater-infiltration beds. Results from total oxidizable precursor assays conducted using groundwater samples collected throughout the plume suggest that some perfluoroalkyl acid precursors at this site are transporting with perfluoroalkyl acids.

Geochemical and hydrologic factors controlling subsurface transport of poly- and perfluoroalkyl substances, Cape Cod, Massachusetts

USGS Publications Warehouse

Weber, Andrea K.; Barber, Larry B.; LeBlanc, Denis R.; Sunderland, Elsie M.; Vecitis, Chad D.

2017-01-01

Growing evidence that certain poly- and perfluoroalkyl substances (PFASs) are associated with negative human health effects prompted the U.S. Environmental Protection Agency to issue lifetime drinking water health advisories for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in 2016. Given that groundwater is a major source of drinking water, the main objective of this work was to investigate geochemical and hydrological processes governing the subsurface transport of PFASs at a former fire training area (FTA) on Cape Cod, Massachusetts, where PFAS-containing aqueous film-forming foams were used historically. A total of 148 groundwater samples and 4 sediment cores were collected along a 1200-m-long downgradient transect originating near the FTA and analyzed for PFAS content. The results indicate that unsaturated zones at the FTA and at hydraulically downgradient former domestic wastewater effluent infiltration beds both act as continuous PFAS sources to the groundwater despite 18 and 20 years of inactivity, respectively. Historically different PFAS sources are evident from contrasting PFAS composition near the water table below the FTA and wastewater-infiltration beds. Results from total oxidizable precursor assays conducted using groundwater samples collected throughout the plume suggest that some perfluoroalkyl acid precursors at this site are transporting with perfluoroalkyl acids.

Supercomputer analysis of sedimentary basins.

PubMed

Bethke, C M; Altaner, S P; Harrison, W J; Upson, C

1988-01-15

Geological processes of fluid transport and chemical reaction in sedimentary basins have formed many of the earth's energy and mineral resources. These processes can be analyzed on natural time and distance scales with the use of supercomputers. Numerical experiments are presented that give insights to the factors controlling subsurface pressures, temperatures, and reactions; the origin of ores; and the distribution and quality of hydrocarbon reservoirs. The results show that numerical analysis combined with stratigraphic, sea level, and plate tectonic histories provides a powerful tool for studying the evolution of sedimentary basins over geologic time.

Geophysical monitoring and reactive transport modeling of ureolytically-driven calcium carbonate precipitation

PubMed Central

2011-01-01

Ureolytically-driven calcium carbonate precipitation is the basis for a promising in-situ remediation method for sequestration of divalent radionuclide and trace metal ions. It has also been proposed for use in geotechnical engineering for soil strengthening applications. Monitoring the occurrence, spatial distribution, and temporal evolution of calcium carbonate precipitation in the subsurface is critical for evaluating the performance of this technology and for developing the predictive models needed for engineering application. In this study, we conducted laboratory column experiments using natural sediment and groundwater to evaluate the utility of geophysical (complex resistivity and seismic) sensing methods, dynamic synchrotron x-ray computed tomography (micro-CT), and reactive transport modeling for tracking ureolytically-driven calcium carbonate precipitation processes under site relevant conditions. Reactive transport modeling with TOUGHREACT successfully simulated the changes of the major chemical components during urea hydrolysis. Even at the relatively low level of urea hydrolysis observed in the experiments, the simulations predicted an enhanced calcium carbonate precipitation rate that was 3-4 times greater than the baseline level. Reactive transport modeling results, geophysical monitoring data and micro-CT imaging correlated well with reaction processes validated by geochemical data. In particular, increases in ionic strength of the pore fluid during urea hydrolysis predicted by geochemical modeling were successfully captured by electrical conductivity measurements and confirmed by geochemical data. The low level of urea hydrolysis and calcium carbonate precipitation suggested by the model and geochemical data was corroborated by minor changes in seismic P-wave velocity measurements and micro-CT imaging; the latter provided direct evidence of sparsely distributed calcium carbonate precipitation. Ion exchange processes promoted through NH4+ production during urea hydrolysis were incorporated in the model and captured critical changes in the major metal species. The electrical phase increases were potentially due to ion exchange processes that modified charge structure at mineral/water interfaces. Our study revealed the potential of geophysical monitoring for geochemical changes during urea hydrolysis and the advantages of combining multiple approaches to understand complex biogeochemical processes in the subsurface. PMID:21943229

Corn stover harvest increases herbicide movement to subsurface drains: RZWQM simulations

USGS Publications Warehouse

Shipitalo, Martin J.; Malone, Robert W.; Ma, Liwang; Nolan, Bernard T.; Kanwar, Rameshwar S.; Shaner, Dale L.; Pederson, Carl H.

2016-01-01

BACKGROUND Crop residue removal for bioenergy production can alter soil hydrologic properties and the movement of agrochemicals to subsurface drains. The Root Zone Water Quality Model (RZWQM), previously calibrated using measured flow and atrazine concentrations in drainage from a 0.4 ha chisel-tilled plot, was used to investigate effects of 50 and 100% corn (Zea mays L.) stover harvest and the accompanying reductions in soil crust hydraulic conductivity and total macroporosity on transport of atrazine, metolachlor, and metolachlor oxanilic acid (OXA). RESULTS The model accurately simulated field-measured metolachlor transport in drainage. A 3-yr simulation indicated that 50% residue removal decreased subsurface drainage by 31% and increased atrazine and metolachlor transport in drainage 4 to 5-fold when surface crust conductivity and macroporosity were reduced by 25%. Based on its measured sorption coefficient, ~ 2-fold reductions in OXA losses were simulated with residue removal. CONCLUSION RZWQM indicated that if corn stover harvest reduces crust conductivity and soil macroporosity, losses of atrazine and metolachlor in subsurface drainage will increase due to reduced sorption related to more water moving through fewer macropores. Losses of the metolachlor degradation product OXA will decrease due to the more rapid movement of the parent compound into the soil.

Spatial and temporal patterns of pesticide losses in a small Swedish agricultural catchment

NASA Astrophysics Data System (ADS)

Sandin, Maria; Piikki, Kristin; Jarvis, Nicholas; Larsbo, Mats; Bishop, Kevin; Kreuger, Jenny

2017-04-01

Research at catchment and regional scales shows that losses of pesticides to surface water often originate from a relatively small fraction of the agricultural landscape. These 'hydrologic source areas' represent areas of land that are highly susceptible to fast transport processes, primarily surface runoff or rapid subsurface flows through soil macropores, either to subsurface field drainage systems or as shallow interflow on more strongly sloping land. A good understanding of the nature of transport pathways for pesticides to surface water in agricultural landscapes is essential for cost-effective identification and implementation of mitigation measures. However, the relative importance of surface and subsurface flows for transport of pesticides to surface waters in Sweden remains largely unknown, since very few studies have been performed under Swedish agro-environmental conditions. We conducted a monitoring study in a small sub-surface drained agricultural catchment in one of the main crop production regions in Sweden. Three small sub-catchments were selected for water sampling based on a high-resolution soil map developed from proximal sensing data; one sub-catchment was dominated by clay soils, another by coarse sandy soils while the third comprised a mix of soil types. Samples were collected from the stream, from field drains discharging into the stream and from within-field surface runoff during spring and early summer in three consecutive years. LC-MS/MS analyses of more than 100 compounds, covering the majority of the polar and semi-polar pesticides most frequently used in Swedish agriculture, were performed on all samples using accredited methods. Information on pesticide applications (products, doses and timing) was obtained from annual interviews with the farmers. There were clear and consistent differences in pesticide losses between the three sub-catchments, with the largest losses occurring in the area with clay soils, and negligible losses from the sandy sub-catchment. This suggests that transport of pesticides to the stream is almost entirely occurring along fast flow paths such as macropore flow to drains or surface runoff. Only a very small proportion of fields are directly connected to the stream by overland pathways, which suggests that macropore flow to drains was the dominant loss pathway in the studied area. Data on pesticide use patterns revealed that compounds were detected in drainage and stream water samples that had not been applied for several years. This suggests that despite the predominant role of fast flow paths in determining losses to the stream, long-term storage along the transport pathways also occurs, presumably in subsoil where degradation is slow.

Microbial-sized, carboxylate-modified microspheres as surrogate tracers in a variety of subsurface environments: An overview

USGS Publications Warehouse

Harvey, Ronald W.; Metge, David W.; LeBlanc, Denis R.

2017-01-01

Since 1986, fluorescent carboxylate-modified polystyrene/latex microspheres (FCM) have been co-injected into aquifers along with conservative tracers and viruses, bacteria, and (or) protozoa. Use of FCM has resulted in new information about subsurface transport behaviors of microorganisms in fractured crystalline rock, karst limestone, soils, and granular aquifers. FCM have been used as surrogates for oocysts of the pathogenic protist Cryptosporidium parvum in karst limestone and granular drinking-water aquifers. The advantages of FCM in subsurface transport studies are that they are safe in tracer applications, negatively charged, easy to detect, chemically inert, and available in wide range of sizes. The limitations of FCM are that the quantities needed for some field transport studies can be prohibitively expensive and that their surface characteristics may not match the microorganisms of interest. These limitations may be ameliorated, in part by using chemically modified FCM so that their surface characteristics are a better match to that of the organisms. Also, more sensitive methods of detection may allow using smaller quantities of FCM. To assess how the transport behaviors of FCM and pathogens might compare at the field scale, it is helpful to conduct side-by-side comparisons of their transport behaviors using the geologic media and site-specific conditions that characterize the field site.

Sources and processes affecting the distribution of dissolved Nd isotopes and concentrations in the West Pacific

NASA Astrophysics Data System (ADS)

Behrens, Melanie K.; Pahnke, Katharina; Schnetger, Bernhard; Brumsack, Hans-Jürgen

2018-02-01

In the Atlantic, where deep circulation is vigorous, the dissolved neodymium (Nd) isotopic composition (expressed as ɛNd) is largely controlled by water mass mixing. In contrast, the factors influencing the ɛNd distribution in the Pacific, marked by sluggish circulation, is not clear yet. Indication for regional overprints in the Pacific is given based on its bordering volcanic islands. Our study aims to clarify the impact and relative importance of different Nd sources (rivers, volcanic islands), vertical (bio)geochemical processes and lateral water mass transport in controlling dissolved ɛNd and Nd concentration ([Nd]) distributions in the West Pacific between South Korea and Fiji. We find indication for unradiogenic continental input from South Korean and Chinese rivers to the East China Sea. In the tropical West Pacific, volcanic islands supply Nd to surface and subsurface waters and modify their ɛNd to radiogenic values of up to +0.7. These radiogenic signatures allow detailed tracing of currents flowing to the east and differentiation from westward currents with open ocean Pacific ɛNd composition in the complex tropical Pacific zonal current system. Modified radiogenic ɛNd of West Pacific intermediate to bottom waters upstream or within our section also indicates non-conservative behavior of ɛNd due to boundary exchange at volcanic island margins, submarine ridges, and with hydrothermal particles. Only subsurface to deep waters (3000 m) in the open Northwest Pacific show conservative behavior of ɛNd. In contrast, we find a striking correlation of extremely low (down to 2.77 pmol/kg Nd) and laterally constant [Nd] with the high-salinity North and South Pacific Tropical Water, indicating lateral transport of preformed [Nd] from the North and South Pacific subtropical gyres into the study area. This observation also explains the previously observed low subsurface [Nd] in the tropical West Pacific. Similarly, Western South Pacific Central Water, Antarctic Intermediate Water, and Lower Circumpolar Deep Water in the southern and equatorial West Pacific are marked by vertically and laterally almost invariant [Nd] indicating a dominance of conservative behavior of [Nd]. In contrast, Central and Intermediate Water in the North West Pacific are characterized by increasing [Nd] with depth reflecting Nd release from particles. Overall, our data demonstrate a dominant lateral transport control on [Nd] distributions and clear non-conservative modification of ɛNd in the West Pacific. The latter affords tracing of surface and subsurface zonal transport in the tropical Pacific, but prevents the use of ɛNd as strictly conservative tracer of the major meridionally circulating water masses in the West Pacific between 15°S and 28°N.

Tracer transport in soils and shallow groundwater: model abstraction with modern tools

USDA-ARS?s Scientific Manuscript database

Vadose zone controls contaminant transport from the surface to groundwater, and modeling transport in vadose zone has become a burgeoning field. Exceedingly complex models of subsurface contaminant transport are often inefficient. Model abstraction is the methodology for reducing the complexity of a...

Urban heat fluxes in the subsurface of Cologne, Germany

NASA Astrophysics Data System (ADS)

Zhu, K.; Bayer, P.; Blum, P.

2012-04-01

Urbanization during the last hundred years has led to both environmental and thermal impacts on the subsurface. The urban heat island (UHI) effect is mostly described as an atmospheric phenomenon, where the measured aboveground temperatures in cities are elevated in comparison to undisturbed rural regions. However, UHIs can be found below, as well as above ground. A large amount of anthropogenic heat migrates into the urban subsurface, which also raises the ground temperature and permanently changes the thermal conditions in shallow aquifers. The main objective of our work is to study and determine the urban heat fluxes in Cologne, Germany, and to improve our understanding of the dynamics of subsurface energy fluxes in UHIs. Ideally, our findings will contribute to strategic and more sustainable geothermal use in cities. For a quantitative analysis of the energy fluxes within the subsurface and across the atmospheric boundary, two and three-dimensional coupled numerical flow and heat transport models were developed. The simulation results indicate that during the past hundred years, an average vertical urban heat flux that ranges between 80 and 375 mW m-2 can be deduced. Thermal anomalies have migrated into the local urban aquifer system and they reach a depth of about 150 m. In this context, the influence of the regional groundwater flow on the subsurface heat transport and temperature development is comprehensively discussed.

Methods of making transportation fuel

DOEpatents

Roes, Augustinus Wilhelmus Maria [Houston, TX; Mo, Weijian [Sugar Land, TX; Muylle, Michel Serge Marie [Houston, TX; Mandema, Remco Hugo [Houston, TX; Nair, Vijay [Katy, TX

2012-04-10

A method for producing alkylated hydrocarbons is disclosed. Formation fluid is produced from a subsurface in situ heat treatment process. The formation fluid is separated to produce a liquid stream and a first gas stream. The first gas stream includes olefins. The liquid stream is fractionated to produce at least a second gas stream including hydrocarbons having a carbon number of at least 3. The first gas stream and the second gas stream are introduced into an alkylation unit to produce alkylated hydrocarbons. At least a portion of the olefins in the first gas stream enhance alkylation. The alkylated hydrocarbons may be blended with one or more components to produce transportation fuel.

Small scale changes of geochemistry and flow field due to transient heat storage in aquifers

NASA Astrophysics Data System (ADS)

Bauer, S.; Boockmeyer, A.; Li, D.; Beyer, C.

2013-12-01

Heat exchangers in the subsurface are increasingly installed for transient heat storage due to the need of heating or cooling of buildings as well as the interim storage of heat to compensate for the temporally fluctuating energy production by wind or solar energy. For heat storage to be efficient, high temperatures must be achieved in the subsurface. Significant temporal changes of the soil and groundwater temperatures however effect both the local flow field by temperature dependent fluid parameters as well as reactive mass transport through temperature dependent diffusion coefficients, geochemical reaction rates and mineral equilibria. As the use of heat storage will be concentrated in urban areas, the use of the subsurface for (drinking) water supply and heat storage will typically coincide and a reliable prognosis of the processes occurring is needed. In the present work, the effects of a temporal variation of the groundwater temperature, as induced by a local heat exchanger introduced into a groundwater aquifer, are studied. For this purpose, the coupled non-isothermal groundwater flow, heat transport and reactive mass transport is simulated in the near filed of such a heat exchanger. By explicitly discretizing and incorporating the borehole, the borehole cementation and the heat exchanger tubes, a realistic geometrical and process representation is obtained. The numerical simulation code OpenGeoSys is used in this work, which incorporates the required processes of coupled groundwater flow, heat and mass transport as well as temperature dependent geochemistry. Due to the use of a Finite Element Method, a close representation of the geometric effects can be achieved. Synthetic scenario simulations for typical settings of salt water formations in northern Germany are used to investigate the geochemical effects arising from a high temperature heat storage by quantifying changes in groundwater chemistry and overall reaction rates. This work presents the simulation approach used and results obtained for the synthetic scenarios. The model simulations show that locally in the direct vicinity of the borehole heat exchanger the flow field is changed, causing a ground water convergence and thus a mixing of water in the case of high temperatures. Also, geochemical reactions are induced due to shifting of temperature dependent mineral equilibria. Due to the moving groundwater, the changes are not reversible, and small impacts remain downstream of the borehole heat exchanger. However, the changes depend strongly on the mineral composition of the formation and the formation water present.

Corn stover harvest increases herbicide movement to subsurface drains – Root Zone Water Quality Model simulations

USDA-ARS?s Scientific Manuscript database

BACKGROUND: Removal of crop residues for bioenergy production can alter soil hydrologic properties, but there is little information on its impact on transport of herbicides and their degradation products to subsurface drains. The Root Zone Water Quality Model, previously calibrated using measured fl...

Long-term electrical resistivity monitoring of recharge-induced contaminant plume behavior.

PubMed

Gasperikova, Erika; Hubbard, Susan S; Watson, David B; Baker, Gregory S; Peterson, John E; Kowalsky, Michael B; Smith, Meagan; Brooks, Scott

2012-11-01

Geophysical measurements, and electrical resistivity tomography (ERT) data in particular, are sensitive to properties that are related (directly or indirectly) to hydrological processes. The challenge is in extracting information from geophysical data at a relevant scale that can be used to gain insight about subsurface behavior and to parameterize or validate flow and transport models. Here, we consider the use of ERT data for examining the impact of recharge on subsurface contamination at the S-3 ponds of the Oak Ridge Integrated Field Research Challenge (IFRC) site in Tennessee. A large dataset of time-lapse cross-well and surface ERT data, collected at the site over a period of 12 months, is used to study time variations in resistivity due to changes in total dissolved solids (primarily nitrate). The electrical resistivity distributions recovered from cross-well and surface ERT data agrees well, and both of these datasets can be used to interpret spatiotemporal variations in subsurface nitrate concentrations due to rainfall, although the sensitivity of the electrical resistivity response to dilution varies with nitrate concentration. Using the time-lapse surface ERT data interpreted in terms of nitrate concentrations, we find that the subsurface nitrate concentration at this site varies as a function of spatial position, episodic heavy rainstorms (versus seasonal and annual fluctuations), and antecedent rainfall history. These results suggest that the surface ERT monitoring approach is potentially useful for examining subsurface plume responses to recharge over field-relevant scales. Published by Elsevier B.V.

Efficiency of magnetorheological fluid finishing on the elimination of defects in fused silica optics

NASA Astrophysics Data System (ADS)

Catrin, R.; Taroux, D.; Cormont, P.; Maunier, C.; Corbineau, T.; Razé, G.; Néauport, J.

2013-09-01

The MegaJoule laser being constructed at the CEA near Bordeaux (France) is designed to focus more than 1 MJ of energy of UV light, on a millimeter scale target in the centre of an experiment chamber. After amplification and transport at the wavelength of 1053 nm, frequency conversion at 351 nm is done with KH2PO4 crystals. The final optic assembly of this system is made up of large fused silica optics, working in transmission, that are used to convey, focus or shape the laser beam. When exposed to fluences of some joules per square centimeter at 351 nm within nanosecond pulse duration, fused silica optics can exhibit localized damage. Damage sites grow exponentially after further laser exposition and therefore dramatically limit the optic lifetime. The nature of the surface finishing process has been established to determine the lifetime of these components under high UV fluences (i.e. more than 5 J/cm2 for 3 ns pulses). Being able to reduce or eliminate the damage initiators such as subsurface cracks present in subsurface damage (SSD) layer of conventionally polished optical components aims this study. Magneto-rheological fluid finishing (MRF) is chosen as a final polishing tool to remove layers of material without inducing further damages. MRF enables to process optics with very small normal stresses applied to the surface during material removal and thus permits the elimination of the residual subsurface cracks. This study offers a better understanding of the efficiency of MRF polishing on the elimination of subsurface cracks in SSD layers.

Influence of cutting parameters on the depth of subsurface deformed layer in nano-cutting process of single crystal copper.

PubMed

Wang, Quanlong; Bai, Qingshun; Chen, Jiaxuan; Su, Hao; Wang, Zhiguo; Xie, Wenkun

2015-12-01

Large-scale molecular dynamics simulation is performed to study the nano-cutting process of single crystal copper realized by single-point diamond cutting tool in this paper. The centro-symmetry parameter is adopted to characterize the subsurface deformed layers and the distribution and evolution of the subsurface defect structures. Three-dimensional visualization and measurement technology are used to measure the depth of the subsurface deformed layers. The influence of cutting speed, cutting depth, cutting direction, and crystallographic orientation on the depth of subsurface deformed layers is systematically investigated. The results show that a lot of defect structures are formed in the subsurface of workpiece during nano-cutting process, for instance, stair-rod dislocations, stacking fault tetrahedron, atomic clusters, vacancy defects, point defects. In the process of nano-cutting, the depth of subsurface deformed layers increases with the cutting distance at the beginning, then decreases at stable cutting process, and basically remains unchanged when the cutting distance reaches up to 24 nm. The depth of subsurface deformed layers decreases with the increase in cutting speed between 50 and 300 m/s. The depth of subsurface deformed layer increases with cutting depth, proportionally, and basically remains unchanged when the cutting depth reaches over 6 nm.

New Frontier in Probing Fluid Transport in Low-Permeability Geomedia: Applications of Elastic and Inelastic Neutron Scattering

NASA Astrophysics Data System (ADS)

Ding, M.; Hjelm, R.; Sussman, A. J.

2016-12-01

Low-permeability geomedia are prevalent in subsurface environments. They have become increasingly important in a wide range of applications such as CO2-sequestration, hydrocarbon recovery, enhanced geothermal systems, legacy waste stewardship, high-level radioactive waste disposal, and global security. The flow and transport characteristics of low-permeability geomedia are dictated by their exceedingly low permeability values ranging from 10-6 to 10-12 darcy with porosities dominated by nanoscale pores. Developing new characterization methods and robust computational models that allow estimation of transport properties of low-permeability geomedia has been identified as a critical basic research and technology development need for controlling subsurface and fluids flow. Due to its sensibility to hydrogen and flexible sample environment, neutron based elastic and inelastic scattering can, through various techniques, interrogate all the nanoscale pores in the sample whether they are fluid accessible or not, and readily characterize interfacial waters. In this presentation, we will present two studies revealing the effects of nanoscale pore confinement on fluid dynamics in geomedia. In one study, we use combined (ultra-small)/small-angle elastic neutron scatterings to probe nanoporous features responses in geological materials to transport processes. In the other study, incoherent inelastic neutron scattering was used to distingwish between intergranular pore water and fluid inclusion moisture in bedded rock salt, and to explore their thermal stablibility. Our work demonstrates that neutron based elastic and inelastic scatterings are techniques of choice for in situ probing hydrocarbon and water behavior in nanoporous materials, providing new insights into water-rock interaction and fluids transport in low-permeability geomaterials.

Intercomparison of Multiscale Modeling Approaches in Simulating Subsurface Flow and Transport

NASA Astrophysics Data System (ADS)

Yang, X.; Mehmani, Y.; Barajas-Solano, D. A.; Song, H. S.; Balhoff, M.; Tartakovsky, A. M.; Scheibe, T. D.

2016-12-01

Hybrid multiscale simulations that couple models across scales are critical to advance predictions of the larger system behavior using understanding of fundamental processes. In the current study, three hybrid multiscale methods are intercompared: multiscale loose-coupling method, multiscale finite volume (MsFV) method and multiscale mortar method. The loose-coupling method enables a parallel workflow structure based on the Swift scripting environment that manages the complex process of executing coupled micro- and macro-scale models without being intrusive to the at-scale simulators. The MsFV method applies microscale and macroscale models over overlapping subdomains of the modeling domain and enforces continuity of concentration and transport fluxes between models via restriction and prolongation operators. The mortar method is a non-overlapping domain decomposition approach capable of coupling all permutations of pore- and continuum-scale models with each other. In doing so, Lagrange multipliers are used at interfaces shared between the subdomains so as to establish continuity of species/fluid mass flux. Subdomain computations can be performed either concurrently or non-concurrently depending on the algorithm used. All the above methods have been proven to be accurate and efficient in studying flow and transport in porous media. However, there has not been any field-scale applications and benchmarking among various hybrid multiscale approaches. To address this challenge, we apply all three hybrid multiscale methods to simulate water flow and transport in a conceptualized 2D modeling domain of the hyporheic zone, where strong interactions between groundwater and surface water exist across multiple scales. In all three multiscale methods, fine-scale simulations are applied to a thin layer of riverbed alluvial sediments while the macroscopic simulations are used for the larger subsurface aquifer domain. Different numerical coupling methods are then applied between scales and inter-compared. Comparisons are drawn in terms of velocity distributions, solute transport behavior, algorithm-induced numerical error and computing cost. The intercomparison work provides support for confidence in a variety of hybrid multiscale methods and motivates further development and applications.

Identification and characterization of natural pipe systems in forested tropical soils

NASA Astrophysics Data System (ADS)

Bovi, Renata Cristina; Moreira, Cesar Augusto; Stucchi Boschi, Raquel; Cooper, Miguel

2017-04-01

Erosive processes on soil surface have been well studied and comprehended by several researchers, however little is known about subsurface erosive processes (piping). Piping is a type of subsurface erosion caused by water flowing in the subsurface and is still considered one of the most difficult erosive processes to be studied. Several processes have been considered as resposible for subsurface erosion and their interaction is complex and difficult to be studied separately. Surface investigations on their own may underestimate the erosion processes, due to the possible occurrence of subsurface processes that are not yet exposed on the surface. The network of subsurface processes should also be understood to better control erosion. Conservation practices that focus on water runoff control may be inefficient if the subsurface flow is not considered. In this study, we aimed to identify and characterize subsurface cavities in the field, as well as understand the network of these cavities, by using geophysical methods (electrical tomography). The study area is situated at the Experimental Station of Tupi, state of São Paulo, Brazil. The soil of the area was classified as Hapludults. The area presents several erosive features, ranging from laminar to permanent gullies and subsurface erosions. The geophysical equipment used was the Terrameter LS resistivity meter, manufactured by ABEM Instruments. The method of electrical tomography was efficient to detect collapsed and non-collapsed pipes. The results presented valuable information to detect areas of risk.

Organic contaminant transport and fate in the subsurface: Evolution of knowledge and understanding

NASA Astrophysics Data System (ADS)

Essaid, Hedeff I.; Bekins, Barbara A.; Cozzarelli, Isabelle M.

2015-07-01

Toxic organic contaminants may enter the subsurface as slightly soluble and volatile nonaqueous phase liquids (NAPLs) or as dissolved solutes resulting in contaminant plumes emanating from the source zone. A large body of research published in Water Resources Research has been devoted to characterizing and understanding processes controlling the transport and fate of these organic contaminants and the effectiveness of natural attenuation, bioremediation, and other remedial technologies. These contributions include studies of NAPL flow, entrapment, and interphase mass transfer that have advanced from the analysis of simple systems with uniform properties and equilibrium contaminant phase partitioning to complex systems with pore-scale and macroscale heterogeneity and rate-limited interphase mass transfer. Understanding of the fate of dissolved organic plumes has advanced from when biodegradation was thought to require oxygen to recognition of the importance of anaerobic biodegradation, multiple redox zones, microbial enzyme kinetics, and mixing of organic contaminants and electron acceptors at plume fringes. Challenges remain in understanding the impacts of physical, chemical, biological, and hydrogeological heterogeneity, pore-scale interactions, and mixing on the fate of organic contaminants. Further effort is needed to successfully incorporate these processes into field-scale predictions of transport and fate. Regulations have greatly reduced the frequency of new point-source contamination problems; however, remediation at many legacy plumes remains challenging. A number of fields of current relevance are benefiting from research advances from point-source contaminant research. These include geologic carbon sequestration, nonpoint-source contamination, aquifer storage and recovery, the fate of contaminants from oil and gas development, and enhanced bioremediation.

Chemical Tracer Methods: Chapter 7

USGS Publications Warehouse

Healy, Richard W.

2017-01-01

Tracers have a wide variety of uses in hydrologic studies: providing quantitative or qualitative estimates of recharge, identifying sources of recharge, providing information on velocities and travel times of water movement, assessing the importance of preferential flow paths, providing information on hydrodynamic dispersion, and providing data for calibration of water flow and solute-transport models (Walker, 1998; Cook and Herczeg, 2000; Scanlon et al., 2002b). Tracers generally are ions, isotopes, or gases that move with water and that can be detected in the atmosphere, in surface waters, and in the subsurface. Heat also is transported by water; therefore, temperatures can be used to trace water movement. This chapter focuses on the use of chemical and isotopic tracers in the subsurface to estimate recharge. Tracer use in surface-water studies to determine groundwater discharge to streams is addressed in Chapter 4; the use of temperature as a tracer is described in Chapter 8.Following the nomenclature of Scanlon et al. (2002b), tracers are grouped into three categories: natural environmental tracers, historical tracers, and applied tracers. Natural environmental tracers are those that are transported to or created within the atmosphere under natural processes; these tracers are carried to the Earth’s surface as wet or dry atmospheric deposition. The most commonly used natural environmental tracer is chloride (Cl) (Allison and Hughes, 1978). Ocean water, through the process of evaporation, is the primary source of atmospheric Cl. Other tracers in this category include chlorine-36 (36Cl) and tritium (3H); these two isotopes are produced naturally in the Earth’s atmosphere; however, there are additional anthropogenic sources of them.

Organic contaminant transport and fate in the subsurface: evolution of knowledge and understanding

USGS Publications Warehouse

Essaid, Hedeff I.; Bekins, Barbara A.; Cozzarelli, Isabelle M.

2015-01-01

Toxic organic contaminants may enter the subsurface as slightly soluble and volatile nonaqueous phase liquids (NAPLs) or as dissolved solutes resulting in contaminant plumes emanating from the source zone. A large body of research published in Water Resources Research has been devoted to characterizing and understanding processes controlling the transport and fate of these organic contaminants and the effectiveness of natural attenuation, bioremediation, and other remedial technologies. These contributions include studies of NAPL flow, entrapment, and interphase mass transfer that have advanced from the analysis of simple systems with uniform properties and equilibrium contaminant phase partitioning to complex systems with pore-scale and macroscale heterogeneity and rate-limited interphase mass transfer. Understanding of the fate of dissolved organic plumes has advanced from when biodegradation was thought to require oxygen to recognition of the importance of anaerobic biodegradation, multiple redox zones, microbial enzyme kinetics, and mixing of organic contaminants and electron acceptors at plume fringes. Challenges remain in understanding the impacts of physical, chemical, biological, and hydrogeological heterogeneity, pore-scale interactions, and mixing on the fate of organic contaminants. Further effort is needed to successfully incorporate these processes into field-scale predictions of transport and fate. Regulations have greatly reduced the frequency of new point-source contamination problems; however, remediation at many legacy plumes remains challenging. A number of fields of current relevance are benefiting from research advances from point-source contaminant research. These include geologic carbon sequestration, nonpoint-source contamination, aquifer storage and recovery, the fate of contaminants from oil and gas development, and enhanced bioremediation.

Integrated geophysical methods for geotechnical subsurface investigations : final report.

DOT National Transportation Integrated Search

2006-01-01

This report summarizes the New Hampshire Department of Transportations (NHDOTs) investigation of : geophysical techniques to supplement conventional test borings and other explorations on transportation projects. : The Departments geotechnic...

Effects of Temperature on Solute Transport Parameters in Differently-Textured Soils at Saturated Condition

NASA Astrophysics Data System (ADS)

Hamamoto, S.; Arihara, M.; Kawamoto, K.; Nishimura, T.; Komatsu, T.; Moldrup, P.

2014-12-01

Subsurface warming driven by global warming, urban heat islands, and increasing use of shallow geothermal heating and cooling systems such as the ground source heat pump, potentially causes changes in subsurface mass transport. Therefore, understanding temperature dependency of the solute transport characteristics is essential to accurately assess environmental risks due to increased subsurface temperature. In this study, one-dimensional solute transport experiments were conducted in soil columns under temperature control to investigate effects of temperature on solute transport parameters, such as solute dispersion and diffusion coefficients, hydraulic conductivity, and retardation factor. Toyoura sand, Kaolin clay, and intact loamy soils were used in the experiments. Intact loamy soils were taken during a deep well boring at the Arakawa Lowland in Saitama Prefecture, Japan. In the transport experiments, the core sample with 5-cm diameter and 4-cm height was first isotropically consolidated, whereafter 0.01M KCl solution was injected to the sample from the bottom. The concentrations of K+ and Cl- in the effluents were analyzed by an ion chromatograph to obtain solute breakthrough curves. The solute transport parameters were calculated from the breakthrough curves. The experiments were conducted under different temperature conditions (15, 25, and 40 oC). The retardation factor for the intact loamy soils decreased with increasing temperature, while water permeability increased due to reduced viscosity of water at higher temperature. Opposite, the effect of temperature on solute dispersivity for the intact loamy soils was insignificant. The effects of soil texture on the temperature dependency of the solute transport characteristics will be further investigated from comparison of results from differently-textured samples.

A chaotic-dynamical conceptual model to describe fluid flow and contaminant transport in a fractured vadose zone. 1997 progress report and presentations at the annual meeting, Ernest Orlando Lawrence Berkeley National Laboratory, December 3--4, 1997

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faybishenko, B.; Doughty, C.; Geller, J.

1998-07-01

Understanding subsurface flow and transport processes is critical for effective assessment, decision-making, and remediation activities for contaminated sites. However, for fluid flow and contaminant transport through fractured vadose zones, traditional hydrogeological approaches are often found to be inadequate. In this project, the authors examine flow and transport through a fractured vadose zone as a deterministic chaotic dynamical process, and develop a model of it in these terms. Initially, the authors examine separately the geometric model of fractured rock and the flow dynamics model needed to describe chaotic behavior. Ultimately they will put the geometry and flow dynamics together to developmore » a chaotic-dynamical model of flow and transport in a fractured vadose zone. They investigate water flow and contaminant transport on several scales, ranging from small-scale laboratory experiments in fracture replicas and fractured cores, to field experiments conducted in a single exposed fracture at a basalt outcrop, and finally to a ponded infiltration test using a pond of 7 by 8 m. In the field experiments, they measure the time-variation of water flux, moisture content, and hydraulic head at various locations, as well as the total inflow rate to the subsurface. Such variations reflect the changes in the geometry and physics of water flow that display chaotic behavior, which they try to reconstruct using the data obtained. In the analysis of experimental data, a chaotic model can be used to predict the long-term bounds on fluid flow and transport behavior, known as the attractor of the system, and to examine the limits of short-term predictability within these bounds. This approach is especially well suited to the need for short-term predictions to support remediation decisions and long-term bounding studies. View-graphs from ten presentations made at the annual meeting held December 3--4, 1997 are included in an appendix to this report.« less

An assessment of the tracer-based approach to quantifying groundwater contributions to streamflow

NASA Astrophysics Data System (ADS)

Jones, J. P.; Sudicky, E. A.; Brookfield, A. E.; Park, Y.-J.

2006-02-01

The use of conservative geochemical and isotopic tracers along with mass balance equations to determine the pre-event groundwater contributions to streamflow during a rainfall event is widely used for hydrograph separation; however, aspects related to the influence of surface and subsurface mixing processes on the estimates of the pre-event contribution remain poorly understood. Moreover, the lack of a precise definition of "pre-event" versus "event" contributions on the one hand and "old" versus "new" water components on the other hand has seemingly led to confusion within the hydrologic community about the role of Darcian-based groundwater flow during a storm event. In this work, a fully integrated surface and subsurface flow and solute transport model is used to analyze flow system dynamics during a storm event, concomitantly with advective-dispersive tracer transport, and to investigate the role of hydrodynamic mixing processes on the estimates of the pre-event component. A number of numerical experiments are presented, including an analysis of a controlled rainfall-runoff experiment, that compare the computed Darcian-based groundwater fluxes contributing to streamflow during a rainfall event with estimates of these contributions based on a tracer-based separation. It is shown that hydrodynamic mixing processes can dramatically influence estimates of the pre-event water contribution estimated by a tracer-based separation. Specifically, it is demonstrated that the actual amount of bulk flowing groundwater contributing to streamflow may be much smaller than the quantity indirectly estimated from a separation based on tracer mass balances, even if the mixing processes are weak.

Researchers Mine Information from Next-Generation Subsurface Flow Simulations

DOE PAGES

Gedenk, Eric D.

2015-12-01

A research team based at Virginia Tech University leveraged computing resources at the US Department of Energy's (DOE's) Oak Ridge National Laboratory to explore subsurface multiphase flow phenomena that can't be experimentally observed. Using the Cray XK7 Titan supercomputer at the Oak Ridge Leadership Computing Facility, the team took Micro-CT images of subsurface geologic systems and created two-phase flow simulations. The team's model development has implications for computational research pertaining to carbon sequestration, oil recovery, and contaminant transport.

Incorporating Water Boiling in the Numerical Modelling of Thermal Remediation by Electrical Resistance Heating

NASA Astrophysics Data System (ADS)

Molnar, I. L.; Krol, M.; Mumford, K. G.

2017-12-01

Developing numerical models for subsurface thermal remediation techniques - such as Electrical Resistive Heating (ERH) - that include multiphase processes such as in-situ water boiling, gas production and recovery has remained a significant challenge. These subsurface gas generation and recovery processes are driven by physical phenomena such as discrete and unstable gas (bubble) flow as well as water-gas phase mass transfer rates during bubble flow. Traditional approaches to multiphase flow modeling soil remain unable to accurately describe these phenomena. However, it has been demonstrated that Macroscopic Invasion Percolation (MIP) can successfully simulate discrete and unstable gas transport1. This has lead to the development of a coupled Electro Thermal-MIP Model2 (ET-MIP) capable of simulating multiple key processes in the thermal remediation and gas recovery process including: electrical heating of soil and groundwater, water flow, geological heterogeneity, heating-induced buoyant flow, water boiling, gas bubble generation and mobilization, contaminant mass transport and removal, and additional mechanisms such as bubble collapse in cooler regions. This study presents the first rigorous validation of a coupled ET-MIP model against two-dimensional water boiling and water/NAPL co-boiling experiments3. Once validated, the model was used to explore the impact of water and co-boiling events and subsequent gas generation and mobilization on ERH's ability to 1) generate, expand and mobilize gas at boiling and NAPL co-boiling temperatures, 2) efficiently strip contaminants from soil during both boiling and co-boiling. In addition, a quantification of the energy losses arising from steam generation during subsurface water boiling was examined with respect to its impact on the efficacy of thermal remediation. While this study specifically targets ERH, the study's focus on examining the fundamental mechanisms driving thermal remediation (e.g., water boiling) renders these results applicable to a wide range of thermal and gas-based remediation techniques. 1. Mumford, K. G., et al. (2010), Adv. Water Resour. 2010, 33 (4), 504-513. 2. Krol, M. M., et al. (2011), Adv. Water Resour. 2011, 34 (4), 537-549. 3. Hegele, P. R. and Mumford, K. G. Journal of Contaminant Hydrology 2014, 165, 24-36.

Subsurface warming in the subpolar North Atlantic during rapid climate events in the Early and Mid-Pleistocene

NASA Astrophysics Data System (ADS)

Hernández-Almeida, Iván; Sierro, Francisco; Cacho, Isabel; Abel Flores, José

2014-05-01

A new high-resolution reconstruction of the temperature and salinity of the subsurface waters using paired Mg/Ca-δ18O measurements on the planktonic foraminifera Neogloboquadrina pachyderma sinistrorsa (sin.) was conducted on a deep-sea sediment core in the subpolar North Atlantic (Site U1314). This study aims to reconstruct millennial-scale subsurface hydrography variations during the Early and Mid-Pleistocene (MIS 31-19). These rapid climate events are characterized by abrupt shifts between warm/cold conditions, and ice-sheet oscillations, as evidenced by major ice rafting events recorded in the North Atlantic sediments (Hernández-Almeida et al., 2012), similar to those found during the Last Glacial period (Marcott et al, 2011). The Mg/Ca derived paleotemperature and salinity oscillations prior and during IRD discharges at Site U1314 are related to changes in intermediate circulation. The increases in Mg/Ca paleotemperatures and salinities during the IRD event are preceded by short episodes of cooling and freshening of subsurface waters. The response of the AMOC to this perturbation is an increased of warm and salty water coming from the south, transported to high latitudes in the North Atlantic beneath the thermocline. This process is accompanied by a southward shift in the convection cell from the Nordic Seas to the subpolar North Atlantic and better ventilation of the North Atlantic at mid-depths. Poleward transport of warm and salty subsurface subtropical waters causes intense basal melting and thinning of marine ice-shelves, that culminates in large-scale instability of the ice sheets, retreat of the grounding line and iceberg discharge. The mechanism proposed involves the coupling of the AMOC with ice-sheet dynamics, and would explain the presence of these fluctuations before the establishment of high-amplitude 100-kyr glacial cycles. Hernández-Almeida, I., Sierro, F.J., Cacho, I., Flores, J.A., 2012. Impact of suborbital climate changes in the North Atlantic on ice sheet dynamics at the Mid-Pleistocene Transition. Paleoceanography 27, PA3214. Marcott, S.A., Clark, P.U., Padman, L., Klinkhammer, G.P., Springer, S.R., Liu, Z., Otto-Bliesner, B.L., Carlson, A.E., Ungerer, A., Padman, J., He, F., Cheng, J., Schmittner, A., 2011. Ice-shelf collapse from subsurface warming as a trigger for Heinrich events. Proceedings of the National Academy of Sciences 108, 13415-13419

Translucent Radiosity: Efficiently Combining Diffuse Inter-Reflection and Subsurface Scattering.

PubMed

Sheng, Yu; Shi, Yulong; Wang, Lili; Narasimhan, Srinivasa G

2014-07-01

It is hard to efficiently model the light transport in scenes with translucent objects for interactive applications. The inter-reflection between objects and their environments and the subsurface scattering through the materials intertwine to produce visual effects like color bleeding, light glows, and soft shading. Monte-Carlo based approaches have demonstrated impressive results but are computationally expensive, and faster approaches model either only inter-reflection or only subsurface scattering. In this paper, we present a simple analytic model that combines diffuse inter-reflection and isotropic subsurface scattering. Our approach extends the classical work in radiosity by including a subsurface scattering matrix that operates in conjunction with the traditional form factor matrix. This subsurface scattering matrix can be constructed using analytic, measurement-based or simulation-based models and can capture both homogeneous and heterogeneous translucencies. Using a fast iterative solution to radiosity, we demonstrate scene relighting and dynamically varying object translucencies at near interactive rates.

Volume reduction outweighs biogeochemical processes in controlling phosphorus treatment in aged detention systems

NASA Astrophysics Data System (ADS)

Shukla, Asmita; Shukla, Sanjay; Annable, Michael D.; Hodges, Alan W.

2017-08-01

Stormwater detention areas (SDAs) play an important role in treating end-of-the-farm runoff in phosphorous (P) limited agroecosystems. Phosphorus transport from the SDAs, including those through subsurface pathways, are not well understood. The prevailing understanding of these systems assumes that biogeochemical processes play the primary treatment role and that subsurface losses can be neglected. Water and P fluxes from a SDA located in a row-crop farm were measured for two years (2009-2011) to assess the SDA's role in reducing downstream P loads. The SDA treated 55% (497 kg) and 95% (205 kg) of the incoming load during Year 1 (Y1, 09-10) and Year 2 (Y2, 10-11), respectively. These treatment efficiencies were similar to surface water volumetric retention (49% in Y1 and 84% in Y2) and varied primarily with rainfall. Similar water volume and P retentions indicate that volume retention is the main process controlling P loads. A limited role of biogeochemical processes was supported by low to no remaining soil P adsorption capacity due to long-term drainage P input. The fact that outflow P concentrations (Y1 = 368.3 μg L- 1, Y2 = 230.4 μg L- 1) could be approximated by using a simple mixing of rainfall and drainage P input further confirmed the near inert biogeochemical processes. Subsurface P losses through groundwater were 304 kg (27% of inflow P) indicating that they are an important source for downstream P. Including subsurface P losses reduces the treatment efficiency to 35% (from 61%). The aboveground biomass in the SDA contained 42% (240 kg) of the average incoming P load suggesting that biomass harvesting could be a cost-effective alternative for reviving the role of biogeochemical processes to enhance P treatment in aged, P-saturated SDAs. The 20-year present economic value of P removal through harvesting was estimated to be 341,000, which if covered through a cost share or a payment for P treatment services program could be a positive outcome for both agriculture and public interests.

Volume reduction outweighs biogeochemical processes in controlling phosphorus treatment in aged detention systems.

PubMed

Shukla, Asmita; Shukla, Sanjay; Annable, Michael D; Hodges, Alan W

2017-08-01

Stormwater detention areas (SDAs) play an important role in treating end-of-the-farm runoff in phosphorous (P) limited agroecosystems. Phosphorus transport from the SDAs, including those through subsurface pathways, are not well understood. The prevailing understanding of these systems assumes that biogeochemical processes play the primary treatment role and that subsurface losses can be neglected. Water and P fluxes from a SDA located in a row-crop farm were measured for two years (2009-2011) to assess the SDA's role in reducing downstream P loads. The SDA treated 55% (497kg) and 95% (205kg) of the incoming load during Year 1 (Y1, 09-10) and Year 2 (Y2, 10-11), respectively. These treatment efficiencies were similar to surface water volumetric retention (49% in Y1 and 84% in Y2) and varied primarily with rainfall. Similar water volume and P retentions indicate that volume retention is the main process controlling P loads. A limited role of biogeochemical processes was supported by low to no remaining soil P adsorption capacity due to long-term drainage P input. The fact that outflow P concentrations (Y1=368.3μg L -1 , Y2=230.4μg L -1 ) could be approximated by using a simple mixing of rainfall and drainage P input further confirmed the near inert biogeochemical processes. Subsurface P losses through groundwater were 304kg (27% of inflow P) indicating that they are an important source for downstream P. Including subsurface P losses reduces the treatment efficiency to 35% (from 61%). The aboveground biomass in the SDA contained 42% (240kg) of the average incoming P load suggesting that biomass harvesting could be a cost-effective alternative for reviving the role of biogeochemical processes to enhance P treatment in aged, P-saturated SDAs. The 20-year present economic value of P removal through harvesting was estimated to be $341,000, which if covered through a cost share or a payment for P treatment services program could be a positive outcome for both agriculture and public interests. Copyright © 2017. Published by Elsevier B.V.

Imaging lateral groundwater flow in the shallow subsurface using stochastic temperature fields

NASA Astrophysics Data System (ADS)

Fairley, Jerry P.; Nicholson, Kirsten N.

2006-04-01

Although temperature has often been used as an indication of vertical groundwater movement, its usefulness for identifying horizontal fluid flow has been limited by the difficulty of obtaining sufficient data to draw defensible conclusions. Here we use stochastic simulation to develop a high-resolution image of fluid temperatures in the shallow subsurface at Borax Lake, Oregon. The temperature field inferred from the geostatistical simulations clearly shows geothermal fluids discharging from a group of fault-controlled hydrothermal springs, moving laterally through the subsurface, and mixing with shallow subsurface flow originating from nearby Borax Lake. This interpretation of the data is supported by independent geochemical and isotopic evidence, which show a simple mixing trend between Borax Lake water and discharge from the thermal springs. It is generally agreed that stochastic simulation can be a useful tool for extracting information from complex and/or noisy data and, although not appropriate in all situations, geostatistical analysis may provide good definition of flow paths in the shallow subsurface. Although stochastic imaging techniques are well known in problems involving transport of species, e.g. delineation of contaminant plumes from soil gas survey data, we are unaware of previous applications to the transport of thermal energy for the purpose of inferring shallow groundwater flow.

Editorial

NASA Astrophysics Data System (ADS)

Bijeljic, Branko; Icardi, Matteo; Prodanović, Maša

2018-05-01

Substantial progress has been made over last few decades on understanding the physics of multiphase flow and reactive transport phenomena in subsurface porous media. Confluence of advances in experimental techniques (including micromodels, X-ray microtomography, Nuclear Magnetic Resonance (NMR)) as well as computational power have made it possible to observe static and dynamic multi-scale flow, transport and reactive processes, thus stimulating development of new generation of modelling tools from pore to field scale. One of the key challenges is to make experiment and models as complementary as possible, with continuously improving experimental methods in order to increase predictive capabilities of theoretical models across scales. This creates need to establish rigorous benchmark studies of flow, transport and reaction in porous media which can then serve as the basis for introducing more complex phenomena in future developments.

An information theory application to improve understanding of subsurface flow and transport conditions at the BARC OPE3 site

USDA-ARS?s Scientific Manuscript database

Improving understanding of subsurface conditions includes comparison and discrimination of concurrent models. Additional observations can be useful for that purpose. The objective of this work was to implement and test a novel method for optimization of selecting locations for additional observation...

Measurements of Capillary Pressure-Saturation Relationships for Silica Sands Using Light Transmission Visualization and a Rapid Pseudo Static Methods

EPA Science Inventory

Measurement of water saturation in porous media is essential for many types of studies including subsurface water flow, subsurface colloids transport and contaminant remediation to name a few. Water saturation (S) in porous media is dependent on the capillary pressure (Pc) which,...

Role of subsurface ocean in decadal climate predictability over the South Atlantic.

PubMed

Morioka, Yushi; Doi, Takeshi; Storto, Andrea; Masina, Simona; Behera, Swadhin K

2018-06-04

Decadal climate predictability in the South Atlantic is explored by performing reforecast experiments using a coupled general circulation model with two initialization schemes; one is assimilated with observed sea surface temperature (SST) only, and the other is additionally assimilated with observed subsurface ocean temperature and salinity. The South Atlantic is known to undergo decadal variability exhibiting a meridional dipole of SST anomalies through variations in the subtropical high and ocean heat transport. Decadal reforecast experiments in which only the model SST is initialized with the observation do not predict well the observed decadal SST variability in the South Atlantic, while the other experiments in which the model SST and subsurface ocean are initialized with the observation skillfully predict the observed decadal SST variability, particularly in the Southeast Atlantic. In-depth analysis of upper-ocean heat content reveals that a significant improvement of zonal heat transport in the Southeast Atlantic leads to skillful prediction of decadal SST variability there. These results demonstrate potential roles of subsurface ocean assimilation in the skillful prediction of decadal climate variability over the South Atlantic.

Control of topography gradients on residence time distributions, mixing dynamics and reactive hotspot development

NASA Astrophysics Data System (ADS)

Bandopadhyay, Aditya; Le Borgne, Tanguy; Davy, Philippe

2017-04-01

Topography-driven subsurface flows are thought to play a central role in determining solute turnover and biogeochemical processes at different scales in the critical zone, including river-hyporheic zone exchanges, hillslope solute transport and reactions, and catchment biogeochemical cycles. Hydraulic head gradients, induced by topography gradients at different scales, generate a distribution of streamlines at depth, dictating the spatial distribution of redox sensitive species, the magnitude of surface water - ground water exchanges and ultimately the source/sink function of the subsurface. Flow velocities generally decrease with depth, leading to broad residence time distributions, which have been shown to affect river chemistry and geochemical reactions in catchments. In this presentation, we discuss the impact of topography-driven flows on mixing processes and the formation of localized reactive hotspots. For this, we solve analytically the coupled flow, mixing and reaction equations in two-dimensional vertical cross-sections of subsurface domains with different topography gradients. For a given topography gradient, we derive the spatial distribution of subsurface velocities, the rates of solute mixing accross streamlines and the induced kinetics of redox, precipitation and dissolution reactions using a Lagrangian approach (Le Borgne et al. 2014). We demonstrate that vertical velocity profiles driven by topography variations, act effectively as shear flows, hence stretching continuously the mixing fronts between recently infiltrated and resident water (Bandopadhyay et al. 2017). We thus derive analytical expressions for residence time distributions, mixing rates and kinetics of chemical reactions as a function of the topography gradients. We show that the rates dissolution and precipitation reactions are significantly enhanced by the existence of vertical velocity gradients and that reaction rates reach a maximum in a localized subsurface reactive layer, whose location and intensity depends on topography gradients. As a consequence of these findings, we discuss the links between topography variations, subsurface velocity gradients and biogeochemical processes in the critical zone. References: Bandopadhyay A., T. Le Borgne, Y. Méheust and M. Dentz (2017) Enhanced reaction kinetics and reactive mixing scale dynamics in mixing fronts under shear flow for arbitrary Damkohler numbers, Adv. in Water Resour. Vol. 100, p. 78-95 Le Borgne T., T. Ginn and M. Dentz (2014) Impact of Fluid Deformation on Mixing-Induced Chemical Reactions in Heterogeneous Flows, Geophys. Res. Lett., Vol. 41, 22, p. 7898-790

E. coli transport through surface-connected biopores identified from smoke injection tests

USDA-ARS?s Scientific Manuscript database

Macropores are the primary mechanism by which fecal bacteria from surface-applied manure can be transported into subsurface drains or shallow groundwater bypassing the soil matrix. Limited research has been performed investigating fecal bacteria transport through specific macropores identified in th...

The Prediction-Focused Approach: An opportunity for hydrogeophysical data integration and interpretation

NASA Astrophysics Data System (ADS)

Hermans, Thomas; Nguyen, Frédéric; Klepikova, Maria; Dassargues, Alain; Caers, Jef

2017-04-01

Hydrogeophysics is an interdisciplinary field of sciences aiming at a better understanding of subsurface hydrological processes. If geophysical surveys have been successfully used to qualitatively characterize the subsurface, two important challenges remain for a better quantification of hydrological processes: (1) the inversion of geophysical data and (2) their integration in hydrological subsurface models. The classical inversion approach using regularization suffers from spatially and temporally varying resolution and yields geologically unrealistic solutions without uncertainty quantification, making their utilization for hydrogeological calibration less consistent. More advanced techniques such as coupled inversion allow for a direct use of geophysical data for conditioning groundwater and solute transport model calibration. However, the technique is difficult to apply in complex cases and remains computationally demanding to estimate uncertainty. In a recent study, we investigate a prediction-focused approach (PFA) to directly estimate subsurface physical properties from geophysical data, circumventing the need for classic inversions. In PFA, we seek a direct relationship between the data and the subsurface variables we want to predict (the forecast). This relationship is obtained through a prior set of subsurface models for which both data and forecast are computed. A direct relationship can often be derived through dimension reduction techniques. PFA offers a framework for both hydrogeophysical "inversion" and hydrogeophysical data integration. For hydrogeophysical "inversion", the considered forecast variable is the subsurface variable, such as the salinity. An ensemble of possible solutions is generated, allowing uncertainty quantification. For hydrogeophysical data integration, the forecast variable becomes the prediction we want to make with our subsurface models, such as the concentration of contaminant in a drinking water production well. Geophysical and hydrological data are combined to derive a direct relationship between data and forecast. We illustrate the process for the design of an aquifer thermal energy storage (ATES) system. An ATES system can theoretically recover in winter the heat stored in the aquifer during summer. In practice, the energy efficiency is often lower than expected due to spatial heterogeneity of hydraulic properties combined to a non-favorable hydrogeological gradient. A proper design of ATES systems should consider the uncertainty of the prediction related to those parameters. With a global sensitivity analysis, we identify sensitive parameters for heat storage prediction and validate the use of a short term heat tracing experiment monitored with geophysics to generate informative data. First, we illustrate how PFA can be used to successfully derive the distribution of temperature in the aquifer from ERT during the heat tracing experiment. Then, we successfully integrate the geophysical data to predict medium-term heat storage in the aquifer using PFA. The result is a full quantification of the posterior distribution of the prediction conditioned to observed data in a relatively limited time budget.

Wells for In Situ Extraction of Volatiles from Regolith (WIEVR)

NASA Technical Reports Server (NTRS)

Walton, Otis R.

2013-01-01

A document discusses WIEVRs, a means to extract water ice more efficiently than previous approaches. This water may exist in subsurface deposits on the Moon, in many NEOs (Near- Earth Objects), and on Mars. The WIEVR approach utilizes heat from the Sun to vaporize subsurface ice; the water (or other volatile) vapor is transported to a surface collection vessel where it is condensed (and collected). The method does not involve mining and extracting regolith before removing the frozen volatiles, so it uses less energy and is less costly than approaches that require mining of regolith. The only drilling required for establishing the WIEVR collection/recovery system is a well-bore drill hole. In its simplest form, the WIEVRs will function without pumps, compressors, or other gas-moving equipment, relying instead on diffusive transport and thermally induced convection of the vaporized volatiles for transport to the collection location(s). These volatile extraction wells could represent a significant advance in extraction efficiency for recovery of frozen volatiles in subsurface deposits on the Moon, Mars, or other extraterrestrial bodies.

Electrode Cultivation and Interfacial Electron Transport in Subsurface Microorganisms

NASA Astrophysics Data System (ADS)

Karbelkar, A. A.; Jangir, Y.; Reese, B. K.; Wanger, G.; Anderson, C.; El-Naggar, M.; Amend, J.

2016-12-01

Continental subsurface environments can present significant energetic challenges to the resident microorganisms. While these environments are geologically diverse, potentially allowing energy harvesting by microorganisms that catalyze redox reactions, many of the abundant electron donors and acceptors are insoluble and therefore not directly bioavailable. Microbes can use extracellular electron transfer (EET) as a metabolic strategy to interact with redox active surfaces. This process can be mimicked on electrode surfaces and hence can lead to enrichment and quantification of subsurface microorganisms A primary bioelectrochemical enrichment with different oxidizing and reducing potentials set up in a single bioreactor was applied in situ to subsurface microorganisms residing in iron oxide rich deposits in the Sanford Underground Research Facility. Secondary enrichment revealed a plethora of classified and unclassified subsurface microbiota on both oxidizing and reducing potentials. From this enrichment, we have isolated a Gram-positive Bacillus along with Gram-negative Cupriavidus and Anaerospora strains (as electrode reducers) and Comamonas (as an electrode oxidizer). The Bacillus and Comamonas isolates were subjected to a detailed electrochemical characterization in half-reactors at anodic and cathodic potentials, respectively. An increase in cathodic current upon inoculation and cyclic voltammetry measurements confirm the hypothesis that Comamonas is capable of electron uptake from electrodes. In addition, measurements of Bacillus on anodes hint towards novel mechanisms that allow EET from Gram-positive bacteria. This study suggests that electrochemical approaches are well positioned to dissect such extracellular interactions that may be prevalent in the subsurface, while using physical electrodes to emulate the microhabitats, redox and geochemical gradients, and the spatially dependent interspecies interactions encountered in the subsurface. Electrochemical characterization of isolated strains can help us establish the possible mechanisms of EET, and hence provide an insight on survival strategies of subsurface microbiota in extreme environments. Continental subsurface environments can present significant energetic challenges to the resident microorganisms. While these environments are geologically diverse, potentially allowing energy harvesting by microorganisms that catalyze redox reactions, many of the abundant electron donors and acceptors are insoluble and therefore not directly bioavailable. Microbes can use extracellular electron transfer (EET) as a metabolic strategy to interact with redox active surfaces. This process can be mimicked on electrode surfaces and hence can lead to enrichment and quantification of subsurface microorganisms A primary bioelectrochemical enrichment with different oxidizing and reducing potentials set up in a single bioreactor was applied in situ to subsurface microorganisms residing in iron oxide rich deposits in the Sanford Underground Research Facility. Secondary enrichment revealed a plethora of classified and unclassified subsurface microbiota on both oxidizing and reducing potentials. From this enrichment, we have isolated a Gram-positive Bacillus along with Gram-negative Cupriavidus and Anaerospora strains (as electrode reducers) and Comamonas (as an electrode oxidizer). The Bacillus and Comamonas isolates were subjected to a detailed electrochemical characterization in half-reactors at anodic and cathodic potentials, respectively. An increase in cathodic current upon inoculation and cyclic voltammetry measurements confirm the hypothesis that Comamonas is capable of electron uptake from electrodes. In addition, measurements of Bacillus on anodes hint towards novel mechanisms that allow EET from Gram-positive bacteria. This study suggests that electrochemical approaches are well positioned to dissect such extracellular interactions that may be prevalent in the subsurface, while using physical electrodes to emulate the microhabitats, redox and geochemical gradients, and the spatially dependent interspecies interactions encountered in the subsurface. Electrochemical characterization of isolated strains can help us establish the possible mechanisms of EET, and hence provide an insight on survival strategies of subsurface microbiota in extreme environments.

Inputs and losses by surface runoff and subsurface leaching for pastures managed by continuous or rotational stocking.

PubMed

Owens, L B; Barker, D J; Loerch, S C; Shipitalo, M J; Bonta, J V; Sulc, R M

2012-01-01

Pasture management practices can affect forage quality and production, animal health and production, and surface and groundwater quality. In a 5-yr study conducted at the North Appalachian Experimental Watershed near Coshocton, Ohio, we compared the effects of two contrasting grazing methods on surface and subsurface water quantity and quality. Four pastures, each including a small, instrumented watershed (0.51-1.09 ha) for surface runoff measurements and a developed spring for subsurface flow collection, received 112 kg N ha(-1) yr(-1) and were grazed at similar stocking rates (1.8-1.9 cows ha(-1)). Two pastures were continuously stocked; two were subdivided so that they were grazed with frequent rotational stocking (5-6 times weekly). In the preceding 5 yr, these pastures received 112 kg N ha(-1) yr(-1) after several years of 0 N fertilizer and were grazed with weekly rotational stocking. Surface runoff losses of N were minimal. During these two periods, some years had precipitation up to 50% greater than the long-term average, which increased subsurface flow and NO(3)-N transport. Average annual NO(3)-N transported in subsurface flow from the four watersheds during the two 5-yr periods ranged from 11.3 to 22.7 kg N ha(-1), which was similar to or less than the mineral-N received in precipitation. Flow and transport variations were greater among seasons than among watersheds. Flow-weighted seasonal NO(3)-N concentrations in subsurface flow did not exceed 7 mg L(-1). Variations in NO(3)-N leached from pastures were primarily due to variable precipitation rather than the effects of continuous, weekly rotational, or frequent rotational stocking practices. This suggests that there was no difference among these grazing practices in terms of NO(3)-N leaching. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Magnetorheological finishing for removing surface and subsurface defects of fused silica optics

NASA Astrophysics Data System (ADS)

Catrin, Rodolphe; Neauport, Jerome; Taroux, Daniel; Cormont, Philippe; Maunier, Cedric; Lambert, Sebastien

2014-09-01

We investigate the capacity of magnetorheological finishing (MRF) process to remove surface and subsurface defects of fused silica optics. Polished samples with engineered surface and subsurface defects were manufactured and characterized. Uniform material removals were performed with a QED Q22-XE machine using different MRF process parameters in order to remove these defects. We provide evidence that whatever the MRF process parameters are, MRF is able to remove surface and subsurface defects. Moreover, we show that MRF induces a pollution of the glass interface similar to conventional polishing processes.

Development of stream-subsurface flow module in sub-daily simulation of Escherichia coli using SWAT

NASA Astrophysics Data System (ADS)

Kim, Minjeong; Boithias, Laurie; Cho, Kyung Hwa; Silvera, Norbert; Thammahacksa, Chanthamousone; Latsachack, Keooudone; Rochelle-Newall, Emma; Sengtaheuanghoung, Oloth; Pierret, Alain; Pachepsky, Yakov A.; Ribolzi, Olivier

2017-04-01

Water contaminated with pathogenic bacteria poses a large threat to public health, especially in the rural areas in the tropics where sanitation and drinking water facilities are often lacking. Several studies have used the Soil and Water Assessment Tool (SWAT) to predict the export of in-stream bacteria at a watershed-scale. However, SWAT is limited to in-stream processes, such as die-off, resuspension and, deposition; and it is usually implemented on a daily time step using the SCS Curve Number method, making it difficult to explore the dynamic fate and transport of bacteria during short but intense events such as flash floods in tropical humid montane headwaters. To address these issues, this study implemented SWAT on an hourly time step using the Green-Ampt infiltration method, and tested the effects of subsurface flow (LATQ+GWQ in SWAT) on bacterial dynamics. We applied the modified SWAT model to the 60-ha Houay Pano catchment in Northern Laos, using sub-daily rainfall and discharge measurements, electric conductivity-derived fractions of overland and subsurface flows, suspended sediments concentrations, and the number of fecal indicator organism Escherichia coli monitored at the catchment outlet from 2011 to 2013. We also took into account land use change by delineating the watershed with the 3-year composite land use map. The results show that low subsurface flow of less than 1 mm recovered the underestimation of E. coli numbers during the dry season, while high subsurface flow caused an overestimation during the wet season. We also found that it is more reasonable to apply the stream-subsurface flow interaction to simulate low in-stream bacteria counts. Using fecal bacteria to identify and understand the possible interactions between overland and subsurface flows may well also provide some insight into the fate of other bacteria, such as those involved in biogeochemical fluxes both in-stream and in the adjacent soils and hyporheic zones.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hammond, Glenn Edward; Bao, J; Huang, M

Hyporheic exchange is a critical mechanism shaping hydrological and biogeochemical processes along a river corridor. Recent studies on quantifying the hyporheic exchange were mostly limited to local scales due to field inaccessibility, computational demand, and complexity of geomorphology and subsurface geology. Surface flow conditions and subsurface physical properties are well known factors on modulating the hyporheic exchange, but quantitative understanding of their impacts on the strength and direction of hyporheic exchanges at reach scales is absent. In this study, a high resolution computational fluid dynamics (CFD) model that couples surface and subsurface flow and transport is employed to simulate hyporheicmore » exchanges in a 7-km long reach along the main-stem of the Columbia River. Assuming that the hyporheic exchange does not affect surface water flow conditions due to its negligible magnitude compared to the volume and velocity of river water, we developed a one-way coupled surface and subsurface water flow model using the commercial CFD software STAR-CCM+. The model integrates the Reynolds-averaged Navier-Stokes (RANS) equation solver with a realizable κ-ε two-layer turbulence model, a two-layer all y + wall treatment, and the volume of fluid (VOF) method, and is used to simulate hyporheic exchanges by tracking the free water-air interface as well as flow in the river and the subsurface porous media. The model is validated against measurements from acoustic Doppler current profiler (ADCP) in the stream water and hyporheic fluxes derived from a set of temperature profilers installed across the riverbed. The validated model is then employed to systematically investigate how hyporheic exchanges are influenced by surface water fluid dynamics strongly regulated by upstream dam operations, as well as subsurface structures (e.g. thickness of riverbed and subsurface formation layers) and hydrogeological properties (e.g. permeability). The results suggest that the thickness of riverbed alluvium layer is the dominant factor for reach-scale hyporheic exchanges, followed by the alluvium permeability, the depth of the underlying impermeable layer, and the assumption of hydrostatic pressure.« less

Debates - Stochastic subsurface hydrology from theory to practice: Introduction

NASA Astrophysics Data System (ADS)

Rajaram, Harihar

2016-12-01

This paper introduces the papers in the "Debates - Stochastic Subsurface Hydrology from Theory to Practice" series. Beginning in the 1970s, the field of stochastic subsurface hydrology has been an active field of research, with over 3500 journal publications, of which over 850 have appeared in Water Resources Research. We are fortunate to have insightful contributions from four groups of distinguished authors who discuss the reasons why the advanced research framework established in stochastic subsurface hydrology has not impacted the practice of groundwater flow and transport modeling and design significantly. There is reasonable consensus that a community effort aimed at developing "toolboxes" for applications of stochastic methods will make them more accessible and encourage practical applications.

Subsurface fate and transport of sulfamethoxazole, 4-nonylphenol, and 17β-estradiol

USGS Publications Warehouse

Barber, L.B.; Meyer, M.T.; LeBlanc, D.R.; Kolpin, Dana W.; Radley, Paul; Chapelle, F.; Rubio, F.

2008-01-01

Subsurface fate and transport of the antibiotic sulfamethoxazole (SX), the non-ionic surfactant degradation product 4-nonylphenol (NP), and the sex hormone 17β-estradiol (E2) were evaluated in a plume of contaminated groundwater at Cape Cod, Massachusetts, USA. The plume is the result of 60 years of wastewater treatment plant effluent disposal into rapid infiltration beds. Natural-gradient, in situ tracer experiments were used to evaluate subsurface transport of SX, NP, and E2 (injected at 300, 530, and 0.55 µg/L, respectively) relative to the conservative tracer bromide. Two geochemical zones were evaluated: (1) uncontaminated groundwater overlying the plume, and (2) contaminated groundwater within the plume that has recently become oxic after decades of anoxic conditions. The uncontaminated groundwater is characterized by a microbial community unacclimated to treated wastewater, whereas the contaminated groundwater is characterized by microbes acclimated to wastewater contaminants. Results from the tracer tests in both zones showed that the antibiotic SX was co-transported with the conservative tracer bromide, with little retardation or mass removal. In contrast, NP and E2, which are more hydrophobic and biodegradable, showed sorption (relative retardation factors ranged up to 5.9) and mass loss at both the uncontaminated and contaminated sites.

Resolving the Multi-scale Behavior of Geochemical Weathering in the Critical Zone Using High Resolution Hydro-geochemical Models

NASA Astrophysics Data System (ADS)

Pandey, S.; Rajaram, H.

2015-12-01

This work investigates hydrologic and geochemical interactions in the Critical Zone (CZ) using high-resolution reactive transport modeling. Reactive transport models can be used to predict the response of geochemical weathering and solute fluxes in the CZ to changes in a dynamic environment, such as those pertaining to human activities and climate change in recent years. The scales of hydrology and geochemistry in the CZ range from days to eons in time and centimeters to kilometers in space. Here, we present results of a multi-dimensional, multi-scale hydro-geochemical model to investigate the role of subsurface heterogeneity on the formation of mineral weathering fronts in the CZ, which requires consideration of many of these spatio-temporal scales. The model is implemented using the reactive transport code PFLOTRAN, an open source subsurface flow and reactive transport code that utilizes parallelization over multiple processing nodes and provides a strong framework for simulating weathering in the CZ. The model is set up to simulate weathering dynamics in the mountainous catchments representative of the Colorado Front Range. Model parameters were constrained based on hydrologic, geochemical, and geophysical observations from the Boulder Creek Critical Zone Observatory (BcCZO). Simulations were performed in fractured rock systems and compared with systems of heterogeneous and homogeneous permeability fields. Tracer simulations revealed that the mean residence time of solutes was drastically accelerated as fracture density increased. In simulations that include mineral reactions, distinct signatures of transport limitations on weathering arose when discrete flow paths were included. This transport limitation was related to both advective and diffusive processes in the highly heterogeneous systems (i.e. fractured media and correlated random permeability fields with σlnk > 3). The well-known time-dependence of mineral weathering rates was found to be the most pronounced in the fractured systems, with a departure from the maximum system-averaged dissolution rate occurring after ~100 kyr followed by a gradual decrease in the reaction rate with time that persists beyond 104 kyr.

A trench study to assess transfer of pesticides in subsurface lateral flow for a soil with contrasting texture on a sloping vineyard in Beaujolais.

PubMed

Peyrard, X; Liger, L; Guillemain, C; Gouy, V

2016-01-01

Subsurface lateral flow in both texture-contrast soils and catchments with shallow bedrock is suspected to be a non-point source of contamination of watercourses by pesticides used in agriculture. As a case study, the north of the Beaujolais region (eastern France) provides a favorable environment for such contamination due to its agro-pedo-climatic conditions. Environments seen in the Beaujolais region include intense viticulture, permeable and shallow soils, steep hillslopes, and storms that occur during the periods of pesticide application. Watercourse contamination by pesticides has been widely observed in this region, and offsite pesticide transport by subsurface lateral flow is suspected to be involved in diffuse and chronic presence of pesticides in surface water. In order to confirm and quantify the potential role of such processes in pesticide transfer, an automated trench system has been designed. The trench was set up on a steep farmed hillslope in a texture-contrast soil. It was equipped with a tipping bucket flow meter and an automatic sampler to monitor pesticide concentrations in lateral flow at fine resolution, by means of a flow-dependent sampling strategy. Four pesticides currently used in vine growing were studied to provide a range of mobility properties: one insecticide (chlorpyrifos-methyl) and three fungicides (spiroxamine, tebuconazole, and dimethomorph). With this system, it was possible to study pesticide concentration dynamics in the subsurface lateral flow, generated by substantial rainfall events following pesticide applications. The experimental design ascertained to be a suitable method in which to monitor subsurface lateral flow and related transfer of pesticides.

Comparison of contaminant transport in agricultural drainage water and urban stormwater runoff

USDA-ARS?s Scientific Manuscript database

Transport of nitrogen and phosphorus from agricultural and urban landscapes to surface water bodies can cause adverse environmental impacts including hypoxia and harmful algal blooms. The main objective of this long-term study was to quantify and compare contaminant transport from a subsurface-drain...

Quantifying subsurface hydrology effects on chemical transport in drainage ditches using a 20-meter flume

USDA-ARS?s Scientific Manuscript database

Agriculture drainage ditches serve as the veins of the Midwestern agricultural landscapes. The transport of chemical fertilizers and pesticides in these ditches affect the local and downstream ecosystems. Although much research has already been conducted on chemical transport in streams and drainage...

Transport of tylosin and tylosin-resistance genes in subsurface drainage water from manured fields

USDA-ARS?s Scientific Manuscript database

Animal agriculture appears to contribute to the spread of antibiotic resistance genes, but few studies have quantified gene transport in agricultural fields. The transport of tylosin, tylosin-resistance genes (erm B, F, A) and tylosin-resistant Enterococcus were measured in tile drainage water from ...

Carbon Tetrachloride Flow and Transport in the Subsurface of the 216-Z-9 Trench at the Hanford Site

NASA Astrophysics Data System (ADS)

Oostrom, M.; Rockhold, M.; Truex, M.; Thorne, P.; Last, G.; Rohay, V.

2006-12-01

Three-dimensional modeling was conducted with layered and heterogeneous models to enhance the conceptual model of CT distribution in the vertical and lateral direction beneath the 216-Z-9 trench and to investigate the effects of soil vapor extraction (SVE). This work supports the U.S. Department of Energy's (DOE's) efforts to characterize the nature and distribution of CT in the 200 West Area and subsequently select an appropriate final remedy. Simulations targeted migration of dense, nonaqueous phase liquid (DNAPL) consisting of CT and co-disposed organics in the subsurface beneath the 216-Z-9 trench as a function of the properties and distribution of subsurface sediments and of the properties and disposal history of the waste. Simulations of CT migration were conducted using the Subsurface Transport Over Multiple Phases (STOMP) simulator. Simulation results support a conceptual model for CT distribution where CT in the DNAPL phase is expected to have migrated primarily in a vertical direction below the disposal trench. Presence of small-scale heterogeneities tends to limit the extent of vertical migration of CT DNAPL due to enhanced retention of DNAPL compared to more homogeneous conditions, but migration is still predominantly in the vertical direction. Results also show that the Cold Creek units retain more CT DNAPL within the vadose zone than other hydrologic unit during SVE. A considerable amount of the disposed CT DNAPL may have partitioned to the vapor and subsequently water and sorbed phases. Presence of small-scale heterogeneities tends to increase the amount of volatilization. Any continued migration of CT from the vadose zone to the groundwater is likely through interaction of vapor phase CT with the groundwater and not through continued DNAPL migration. The results indicated that SVE appears to be an effective technology for vadose zone remediation, but additional effort is needed to improve simulation of the SVE process.

Mineral solubility and free energy controls on microbial reaction kinetics: Application to contaminant transport in the subsurface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taillefert, Martial; Van Cappellen, Philippe

Recent developments in the theoretical treatment of geomicrobial reaction processes have resulted in the formulation of kinetic models that directly link the rates of microbial respiration and growth to the corresponding thermodynamic driving forces. The overall objective of this project was to verify and calibrate these kinetic models for the microbial reduction of uranium(VI) in geochemical conditions that mimic as much as possible field conditions. The approach combined modeling of bacterial processes using new bioenergetic rate laws, laboratory experiments to determine the bioavailability of uranium during uranium bioreduction, evaluation of microbial growth yield under energy-limited conditions using bioreactor experiments, competitionmore » experiments between metabolic processes in environmentally relevant conditions, and model applications at the field scale. The new kinetic descriptions of microbial U(VI) and Fe(III) reduction should replace those currently used in reactive transport models that couple catabolic energy generation and growth of microbial populations to the rates of biogeochemical redox processes. The above work was carried out in collaboration between the groups of Taillefert (batch reactor experiments and reaction modeling) at Georgia Tech and Van Cappellen (retentostat experiments and reactive transport modeling) at University of Waterloo (Canada).« less

Integrating Geochemical Reactions with a Particle-Tracking Approach to Simulate Nitrogen Transport and Transformation in Aquifers

NASA Astrophysics Data System (ADS)

Cui, Z.; Welty, C.; Maxwell, R. M.

2011-12-01

Lagrangian, particle-tracking models are commonly used to simulate solute advection and dispersion in aquifers. They are computationally efficient and suffer from much less numerical dispersion than grid-based techniques, especially in heterogeneous and advectively-dominated systems. Although particle-tracking models are capable of simulating geochemical reactions, these reactions are often simplified to first-order decay and/or linear, first-order kinetics. Nitrogen transport and transformation in aquifers involves both biodegradation and higher-order geochemical reactions. In order to take advantage of the particle-tracking approach, we have enhanced an existing particle-tracking code SLIM-FAST, to simulate nitrogen transport and transformation in aquifers. The approach we are taking is a hybrid one: the reactive multispecies transport process is operator split into two steps: (1) the physical movement of the particles including the attachment/detachment to solid surfaces, which is modeled by a Lagrangian random-walk algorithm; and (2) multispecies reactions including biodegradation are modeled by coupling multiple Monod equations with other geochemical reactions. The coupled reaction system is solved by an ordinary differential equation solver. In order to solve the coupled system of equations, after step 1, the particles are converted to grid-based concentrations based on the mass and position of the particles, and after step 2 the newly calculated concentration values are mapped back to particles. The enhanced particle-tracking code is capable of simulating subsurface nitrogen transport and transformation in a three-dimensional domain with variably saturated conditions. Potential application of the enhanced code is to simulate subsurface nitrogen loading to the Chesapeake Bay and its tributaries. Implementation details, verification results of the enhanced code with one-dimensional analytical solutions and other existing numerical models will be presented in addition to a discussion of implementation challenges.

Hydraulic and geochemical framework of the Idaho National Engineering and Environmental Laboratory vadose zone

USGS Publications Warehouse

Nimmo, John R.; Rousseau, Joseph P.; Perkins, Kim S.; Stollenwerk, Kenneth G.; Glynn, Pierre D.; Bartholomay, Roy C.; Knobel, LeRoy L.

2004-01-01

Questions of major importance for subsurface contaminant transport at the Idaho National Engineering and Environmental Laboratory (INEEL) include (i) travel times to the aquifer, both average or typical values and the range of values to be expected, and (ii) modes of contaminant transport, especially sorption processes. The hydraulic and geochemical framework within which these questions are addressed is dominated by extreme heterogeneity in a vadose zone and aquifer consisting of interbedded basalts and sediments. Hydraulically, major issues include diverse possible types of flow pathways, extreme anisotropy, preferential flow, combined vertical and horizontal flow, and temporary saturation or perching. Geochemically, major issues include contaminant mobility as influenced by redox conditions, the concentration of organic and inorganic complexing solutes and other local variables, the interaction with infiltrating waters and with the contaminant source environment, and the aqueous speciation of contaminants such as actinides. Another major issue is the possibility of colloid transport, which inverts some of the traditional concepts of mobility, as sorbed contaminants on mobile colloids may be transported with ease compared with contaminants that are not sorbed. With respect to the goal of minimizing aquifer concentrations of contaminants, some characteristics of the vadose zone are essentially completely favorable. Examples include the great thickness (200 m) of the vadose zone, and the presence of substantial quantities of fine sediments that can retard contaminant transport both hydraulically and chemically. Most characteristics, however, have both favorable and unfavorable aspects. For example, preferential flow, as promoted by several notable features of the vadose zone at the INEEL, can provide fast, minimally sorbing pathways for contaminants to reach the aquifer easily, but it also leads to a wide dispersal of contaminants in a large volume of subsurface material, thus increasing the opportunity for dilution and sorption.

Transformation of zinc-concentrate in surface and subsurface environments: Implications for assessing zinc mobility/toxicity and choosing an optimal remediation strategy.

PubMed

Kwon, Man Jae; Boyanov, Maxim I; Yang, Jung-Seok; Lee, Seunghak; Hwang, Yun Ho; Lee, Ju Yeon; Mishra, Bhoopesh; Kemner, Kenneth M

2017-07-01

Zinc contamination in near- and sub-surface environments is a serious threat to many ecosystems and to public health. Sufficient understanding of Zn speciation and transport mechanisms is therefore critical to evaluating its risk to the environment and to developing remediation strategies. The geochemical and mineralogical characteristics of contaminated soils in the vicinity of a Zn ore transportation route were thoroughly investigated using a variety of analytical techniques (sequential extraction, XRF, XRD, SEM, and XAFS). Imported Zn-concentrate (ZnS) was deposited in a receiving facility and dispersed over time to the surrounding roadside areas and rice-paddy soils. Subsequent physical and chemical weathering resulted in dispersal into the subsurface. The species identified in the contaminated areas included Zn-sulfide, Zn-carbonate, other O-coordinated Zn-minerals, and Zn species bound to Fe/Mn oxides or clays, as confirmed by XAFS spectroscopy and sequential extraction. The observed transformation from S-coordinated Zn to O-coordinated Zn associated with minerals suggests that this contaminant can change into more soluble and labile forms as a result of weathering. For the purpose of developing a soil washing remediation process, the contaminated samples were extracted with dilute acids. The extraction efficiency increased with the increase of O-coordinated Zn relative to S-coordinated Zn in the sediment. This study demonstrates that improved understanding of Zn speciation in contaminated soils is essential for well-informed decision making regarding metal mobility and toxicity, as well as for choosing an appropriate remediation strategy using soil washing. Copyright © 2017 Elsevier Ltd. All rights reserved.

Biogeographic congruency among bacterial communities from terrestrial sulfidic springs

PubMed Central

Headd, Brendan; Engel, Annette S.

2014-01-01

Terrestrial sulfidic springs support diverse microbial communities by serving as stable conduits for geochemically diverse and nutrient-rich subsurface waters. Microorganisms that colonize terrestrial springs likely originate from groundwater, but may also be sourced from the surface. As such, the biogeographic distribution of microbial communities inhabiting sulfidic springs should be controlled by a combination of spring geochemistry and surface and subsurface transport mechanisms, and not necessarily geographic proximity to other springs. We examined the bacterial diversity of seven springs to test the hypothesis that occurrence of taxonomically similar microbes, important to the sulfur cycle, at each spring is controlled by geochemistry. Complementary Sanger sequencing and 454 pyrosequencing of 16S rRNA genes retrieved five proteobacterial classes, and Bacteroidetes, Chlorobi, Chloroflexi, and Firmicutes phyla from all springs, which suggested the potential for a core sulfidic spring microbiome. Among the putative sulfide-oxidizing groups (Epsilonproteobacteria and Gammaproteobacteria), up to 83% of the sequences from geochemically similar springs clustered together. Abundant populations of Hydrogenimonas-like or Sulfurovum-like spp. (Epsilonproteobacteria) occurred with abundant Thiothrix and Thiofaba spp. (Gammaproteobacteria), but Arcobacter-like and Sulfurimonas spp. (Epsilonproteobacteria) occurred with less abundant gammaproteobacterial populations. These distribution patterns confirmed that geochemistry rather than biogeography regulates bacterial dominance at each spring. Potential biogeographic controls were related to paleogeologic sedimentation patterns that could control long-term microbial transport mechanisms that link surface and subsurface environments. Knowing the composition of a core sulfidic spring microbial community could provide a way to monitor diversity changes if a system is threatened by anthropogenic processes or climate change. PMID:25250021

Transformation of zinc-concentrate in surface and subsurface environments: Implications for assessing zinc mobility/toxicity and choosing an optimal remediation strategy

DOE PAGES

Kwon, Man Jae; Boyanov, Maxim I.; Yang, Jung -Seok; ...

2017-03-24

Zinc contamination in near- and sub-surface environments is a serious threat to many ecosystems and to public health. Sufficient understanding of Zn speciation and transport mechanisms is therefore critical to evaluating its risk to the environment and to developing remediation strategies. The geochemical and mineralogical characteristics of contaminated soils in the vicinity of a Zn ore transportation route were thoroughly investigated using a variety of analytical techniques (sequential extraction, XRF, XRD, SEM, and XAFS). Imported Zn-concentrate (ZnS) was deposited in a receiving facility and dispersed over time to the surrounding roadside areas and rice-paddy soils. Subsequent physical and chemical weatheringmore » resulted in dispersal into the subsurface. The species identified in the contaminated areas included Zn-sulfide, Zn-carbonate, other O-coordinated Zn-minerals, and Zn species bound to Fe/Mn oxides or clays, as confirmed by XAFS spectroscopy and sequential extraction. The observed transformation from S-coordinated Zn to O-coordinated Zn associated with minerals suggests that this contaminant can change into more soluble and labile forms as a result of weathering. For the purpose of developing a soil washing remediation process, the contaminated samples were extracted with dilute acids. The extraction efficiency increased with the increase of O-coordinated Zn relative to S-coordinated Zn in the sediment. Furthermore, this study demonstrates that improved understanding of Zn speciation in contaminated soils is essential for well-informed decision making regarding metal mobility and toxicity, as well as for choosing an appropriate remediation strategy using soil washing.« less

Hydrogeologic controls on nitrate transport in a small agricultural catchment, Iowa

USGS Publications Warehouse

Schilling, K.E.; Tomer, M.D.; Zhang, Y.-K.; Weisbrod, T.; Jacobson, P.; Cambardella, C.A.

2007-01-01

Effects of subsurface deposits on nitrate loss in stream riparian zones are recognized, but little attention has been focused on similar processes occurring in upland agricultural settings. In this paper, we evaluated hydrogeologic controls on nitrate transport processes occurring in a small 7.6 ha Iowa catchment. Subsurface deposits in the catchment consisted of upland areas of loess overlying weathered pre-Illinoian till, drained by two ephemeral drainageways that consisted of Holocene-age silty and organic rich alluvium. Water tables in upland areas fluctuated more than 4 m per year compared to less than 0.3 m in the drainageway. Water quality patterns showed a distinct spatial pattern, with groundwater in the drainageways having lower nitrate concentrations (10 mg L-1) as wells as lower pH, dissolved oxygen and redox, and higher ammonium and dissolved organic carbon levels. Several lines of evidence suggested that conditions are conducive for denitrification of groundwater flowing from uplands through the drainageways. Field-measured nitrate decay rates in the drainageways (???0.02 day-1) were consistent with other laboratory studies and regional patterns. Results from MODFLOW and MT3DMS simulations indicated that soils in the ephemeral drainageways could process all upland groundwater nitrate flowing through them. However, model-simulated tile drainage increased both water flux and nitrate loss from the upland catchment. Study results suggest that ephemeral drainageways can provide a natural nitrate treatment system in our upland glaciated catchments, offering management opportunities to reduce nitrate delivery to streams. Copyright 2007 by the American Geophysical Union.

A three-component hydrograph separation based on geochemical tracers in a tropical mountainous headwater catchment in northern Thailand

NASA Astrophysics Data System (ADS)

Hugenschmidt, C.; Ingwersen, J.; Sangchan, W.; Sukvanachaikul, Y.; Duffner, A.; Uhlenbrook, S.; Streck, T.

2014-02-01

Land-use change in the mountainous parts of northern Thailand is reflected by an increased application of agrochemicals, which may be lost to surface and groundwater. The close relation between flow paths and contaminant transport within hydrological systems requires recognizing and understanding the dominant hydrological processes. To date, the vast majority of studies on runoff generation have been conducted in temperate regions. Tropical regions suffer from a general lack of data, and little is known about runoff generation processes. To fill this knowledge gap, a three-component hydrograph separation based on geochemical tracers was carried out in a steep, remote and monsoon-dominated study site (7 km2) in northern Thailand. Silica and electrical conductivity (EC) were identified as useful tracers and were applied to calculate the fractions of groundwater (similar to pre-event water), shallow subsurface flow and surface runoff on stormflow. K+ was a useful indicator for surface runoff dynamics, and Ca2+ provided insights into groundwater behaviour. Nevertheless, neither measure was applicable for the quantification of runoff components. Cl- and further parameters (e.g. Na+, K+, and Mg2+) were also not helpful for flow path identification, nor were their concentrations distinguishable among the components. Groundwater contributed the largest fractions to stormflow (62-80%) throughout all events, followed by shallow subsurface flow (17-36%) and surface runoff (2-13%). Our results provide important insights into the dynamics of the runoff processes in the study area and may be used to assess the transport pattern of contaminants (i.e. agrochemicals) here.

Reactive Transport Modeling of Subsurface Arsenic Removal Systems in Rural Bangladesh

NASA Astrophysics Data System (ADS)

Bakker, M.; Rahman, M. M.; van Breukelen, B. M.; Ahmed, K. M.

2014-12-01

Elevated concentrations of arsenic (As) in the groundwater of the shallow aquifers of Bangladesh are a major public health concern. Subsurface Arsenic Removal (SAR) is a relatively new treatment option that can potentially be a cost effective method for arsenic removal for community-based drinking water supplies. The basic idea of SAR is to extract water, aerate it, and re-inject it, after which groundwater with reduced arsenic concentrations may be extracted. The main process for As reduction is sorption to Hydrous Ferric Oxides (HFO) that forms after injection of the aerated water. The purpose of this poster is to investigate the major geochemical processes responsible for the (im)mobilization of As during SAR operation. SAR was applied at a test site in Muradnagar upazila in Comilla district about 100 km southeast of Dhaka in Bangladesh. Multiple extraction/aeration/re-injection cycles were performed and water samples were analyzed. A PHREEQC reactive transport model (RTM) was used in a radial flow setting to try to reproduce the measurements. Kinetic oxidation/dissolution reactions, cation exchange, and surface complexation were simulated. The simulation of different reactions enables the possibility to discern the reaction parameters involved in the im(mobilization) of As. The model fit has reasonable agreement with the observed data for major ions and trace elements. The model suggests an increasing sorption capacity due to the gradual development of HFO precipitates resulting from the injection phases. Modeled breakthrough curves of As, Fe(II), and Mn, match the measured increase of As, Fe(II), and Mn removal with successive cycles. The model illustrates that the pH of groundwater during SAR operation has a great impact on As sorption in the subsurface. The surface complexation modeling suggests that competitive displacement of As by H4SiO4 is an important factor limiting As removal during SAR operation.

Spatial Autocorrelation, Source Water and the Distribution of Total and Viable Microbial Abundances within a Crystalline Formation to a Depth of 800 m

PubMed Central

Beaton, E. D.; Stuart, Marilyne; Stroes-Gascoyne, Sim; King-Sharp, Karen J.; Gurban, Ioana; Festarini, Amy; Chen, Hui Q.

2017-01-01

Proposed radioactive waste repositories require long residence times within deep geological settings for which we have little knowledge of local or regional subsurface dynamics that could affect the transport of hazardous species over the period of radioactive decay. Given the role of microbial processes on element speciation and transport, knowledge and understanding of local microbial ecology within geological formations being considered as host formations can aid predictions for long term safety. In this relatively unexplored environment, sampling opportunities are few and opportunistic. We combined the data collected for geochemistry and microbial abundances from multiple sampling opportunities from within a proposed host formation and performed multivariate mixing and mass balance (M3) modeling, spatial analysis and generalized linear modeling to address whether recharge can explain how subsurface communities assemble within fracture water obtained from multiple saturated fractures accessed by boreholes drilled into the crystalline formation underlying the Chalk River Laboratories site (Deep River, ON, Canada). We found that three possible source waters, each of meteoric origin, explained 97% of the samples, these are: modern recharge, recharge from the period of the Laurentide ice sheet retreat (ca. ∼12000 years before present) and a putative saline source assigned as Champlain Sea (also ca. 12000 years before present). The distributed microbial abundances and geochemistry provide a conceptual model of two distinct regions within the subsurface associated with bicarbonate – used as a proxy for modern recharge – and manganese; these regions occur at depths relevant to a proposed repository within the formation. At the scale of sampling, the associated spatial autocorrelation means that abundances linked with geochemistry were not unambiguously discerned, although fine scale Moran’s eigenvector map (MEM) coefficients were correlated with the abundance data and suggest the action of localized processes possibly associated with the manganese and sulfate content of the fracture water. PMID:28974945

Conceptual Model of Iodine Behavior in the Subsurface at the Hanford Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Truex, Michael J.; Lee, Brady D.; Johnson, Christian D.

Isotopes of iodine were generated during plutonium production within the nine production reactors at the U.S. Department of Energy Hanford Site. The short half-life 131I that was released from the fuel into the atmosphere during the dissolution process (when the fuel was dissolved) in the Hanford Site 200 Area is no longer present at concentrations of concern in the environment. The long half-life 129I generated at the Hanford Site during reactor operations was (1) stored in single-shell and double-shell tanks, (2) discharged to liquid disposal sites (e.g., cribs and trenches), (3) released to the atmosphere during fuel reprocessing operations, ormore » (4) captured by off-gas absorbent devices (silver reactors) at chemical separations plants (PUREX, B-Plant, T-Plant, and REDOX). Releases of 129I to the subsurface have resulted in several large, though dilute, plumes in the groundwater. There is also 129I remaining in the vadose zone beneath disposal or leak locations. The fate and transport of 129I in the environment and potential remediation technologies are currently being studied as part of environmental remediation activities at the Hanford Site. A conceptual model describing the nature and extent of subsurface contamination, factors that control plume behavior, and factors relevant to potential remediation processes is needed to support environmental remedy decisions. Because 129I is an uncommon contaminant, relevant remediation experience and scientific literature are limited. In addition, its behavior in subsurface is different from that of other more common and important contaminants (e.g., U, Cr and Tc) in terms of sorption (adsorption and precipitation), and aqueous phase species transformation via redox reactions. Thus, the conceptual model also needs to both describe known contaminant and biogeochemical process information and identify aspects about which additional information is needed to effectively support remedy decisions.« less

Linking Surface Topography Variations To Subsurface Mixing And Reaction Patterns

NASA Astrophysics Data System (ADS)

Le Borgne, T.; Bandopadhyay, A.; Davy, P.

2017-12-01

Fluctuations in surface topography generate nested streamline patterns in the subsurface over scales ranging from millimeters to kilometers. Because solute residence times can be very different for each streamlines, these patterns exert a strong control on biogeochemical reactions. While this effect has been quantified in reactive transport models, solute transfer across streamlines has been generally neglected. Yet, this process can lead to significant solute dilution and may trigger reactions by mixing water with different chemical compositions. Considering topography-driven subsurface flow cells of different sizes, we show that the resulting streamline structures act as shear flows, with shear rates that can vary over orders of magnitude depending on scale, permeability and hydraulic head gradient. This leads to the formation of localized layers of enhanced dilution and reaction, where mixing rates can be orders of magnitude larger than diffusion limited rates (Bandopadhyay et al. under review). We develop a theoretical model that predicts the depth and magnitude of these mixing hotspots and quantifies the resulting exports of conservative and reactive chemical species at discharge locations. We discuss consequences of these findings by applying this model at hyporheic zone, hillslope, and catchment scales.

Silica-coated titania and zirconia colloids for subsurface transport field experiments

USGS Publications Warehouse

Ryan, Joseph N.; Elimelech, Menachem; Baeseman, Jenny L.; Magelky, Robin D.

2000-01-01

Silica-coated titania (TiO2) and zirconia (ZrO2) colloids were synthesized in two sizes to provide easily traced mineral colloids for subsurface transport experiments. Electrophoretic mobility measurements showed that coating with silica imparted surface properties similar to pure silica to the titania and zirconia colloids. Measurements of steady electrophoretic mobility and size (by dynamic light scattering) over a 90-day period showed that the silica-coated colloids were stable to aggregation and loss of coating. A natural gradient field experiment conducted in an iron oxide-coated sand and gravel aquifer also showed that the surface properties of the silica-coated colloids were similar. Colloid transport was traced at μg L-1 concentrations by inductively coupled plasma-atomic emission spectroscopy measurement of Ti and Zr in acidified samples.

Controls on radium transport by adsorption to iron minerals

NASA Astrophysics Data System (ADS)

Chen, M.; Wang, T.; Kocar, B. D.

2015-12-01

Radium is a naturally occurring radioactive metal found in many subsurface environments. Radium isotopes are generated by uranium and thorium decay, and are particularly abundant within groundwaters where minimal porewater flux leads to accumulation. These isotopes are used as natural tracers for estimating submarine groundwater discharge (SGD) [1], allowing for large scale estimation of GW fluxes into and out of the ocean [2]. They also represent a substantial hazard in wastewater produced after hydraulic fracturing for natural gas extraction [3], resulting in a significant risk of environmental release to surface and near-surface waters, and increased cost for water treatment or disposal. Adsorption to mineral surfaces represents a dominant pathway of radium retention in subsurface environments. For SGD studies, adsorption processes impact estimates of GW fluxes, while in hydraulic fracturing, radium adsorption to aquifer solids mediates wastewater radium activities. Analysis of past sorption studies revealed large variability in partition coefficients [4], while examination of radium adsorption kinetics and surface complexation have only recently started [5]. Accordingly, we present the results of sorption and column experiments of radium with a suite of iron minerals representative of those found within deep saline and near-surface (freshwater) aquifers, and evaluate impacts of varying salinity solutions through artificial waters. Further, we explore the impacts of pyrite oxidation and ferrihydrite transformation to other iron-bearing secondary minerals on the transport and retention of radium. These results will provide critical information on the mineralogical controls on radium retention in subsurface environments, and will therefore improve predictions of radium groundwater transport in natural and contaminated systems. [1] Charette, M.A., Buesseler, K.O. & Andrews, J.E., Limnol. Oceanogr. (2001). [2] Moore, W.S., Ann. Rev. Mar. Sci. (2010). [3] Vengosh, A. et al. Environ. Sci. Technol., (2014). [4] Beck, A., Cochran, M., Marine Chem., (2013). [5] Sajih, M. et al. Geochim. Cosmochim. AC. (2014).

Compositions produced using an in situ heat treatment process

DOEpatents

Roes, Augustinus Wilhelmus Maria; Nair, Vijay; Munsterman, Erwin Hunh; Van Bergen, Petrus Franciscus; Van Den Berg, Franciscus Gondulfus Antonius

2013-05-28

Methods for treating a subsurface formation and compositions produced therefrom are described herein. At least one method for producing hydrocarbons from a subsurface formation includes providing heat to the subsurface formation using an in situ heat treatment process. One or more formation particles may be formed during heating of the subsurface formation. Fluid that includes hydrocarbons and the formation particles may be produced from the subsurface formation. The formation particles in the produced fluid may include cenospheres and have an average particle size of at least 0.5 micrometers.

Compositions produced using an in situ heat treatment process

DOEpatents

Roes, Augustinus Wilhelmus Maria [Houston, TX; Nair, Vijay [Katy, TX; Munsterman, Erwin Henh [Amsterdam, NL; Van Bergen, Petrus Franciscus [Amsterdam, NL; Van Den Berg, Franciscus Gondulfus Antonius

2009-10-20

Systems, methods, and heaters for treating a subsurface formation are described herein. At least one method for producing hydrocarbons from a subsurface formation includes providing heat to the subsurface formation using an in situ heat treatment process. One or more formation particles may be formed during heating of the subsurface formation. Fluid that includes hydrocarbons and the formation particles may be produced from the subsurface formation. The formation particles in the produced fluid may include cenospheres and have an average particle size of at least 0.5 micrometers.

Upscaling of reaction rates in reactive transport using pore-scale reactive transport model

NASA Astrophysics Data System (ADS)

Yoon, H.; Dewers, T. A.; Arnold, B. W.; Major, J. R.; Eichhubl, P.; Srinivasan, S.

2013-12-01

Dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes among hydrodynamics, transport, and reactions at the (sub) pore-scale. In this research pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reaction at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This work is motivated by the observed CO2 seeps from a natural analog to geologic CO2 sequestration at Crystal Geyser, Utah. A key observation is the lateral migration of CO2 seep sites at a scale of ~ 100 meters over time. A pore-scale model provides fundamental mechanistic explanations of how calcite precipitation alters flow paths by pore plugging under different geochemical compositions and pore configurations. In addition, response function of reaction rates will be constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Damkohler and Peclet numbers. Newly developed response functions will be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO2 seeps. Comparison of field observations and simulations results will provide mechanistic explanations of the lateral migration and enhance our understanding of subsurface processes associated with the CO2 injection. This work is supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

On the non-uniqueness of the hydro-geomorphic responses in a zero-order catchment with respect to soil moisture

NASA Astrophysics Data System (ADS)

Kim, Jongho; Dwelle, M. Chase; Kampf, Stephanie K.; Fatichi, Simone; Ivanov, Valeriy Y.

2016-06-01

This study advances mechanistic interpretation of predictability challenges in hydro-geomorphology related to the role of soil moisture spatial variability. Using model formulations describing the physics of overland flow, variably saturated subsurface flow, and erosion and sediment transport, this study explores (1) why a basin with the same mean soil moisture can exhibit distinctly different spatial moisture distributions, (2) whether these varying distributions lead to non-unique hydro-geomorphic responses, and (3) what controls non-uniqueness in relation to the response type. Two sets of numerical experiments are carried out with two physically-based models, HYDRUS and tRIBS+VEGGIE+FEaST, and their outputs are analyzed with respect to pre-storm moisture state. The results demonstrate that distinct spatial moisture distributions for the same mean wetness arise because near-surface soil moisture dynamics exhibit different degrees of coupling with deeper-soil moisture and the process of subsurface drainage. The consequences of such variations are different depending on the type of hydrological response. Specifically, if the predominant runoff response is of infiltration excess type, the degree of non-uniqueness is related to the spatial distribution of near-surface moisture. If runoff is governed by subsurface stormflow, the extent of deep moisture contributing area and its "readiness to drain" determine the response characteristics. Because the processes of erosion and sediment transport superimpose additional controls over factors governing runoff generation and overland flow, non-uniqueness of the geomorphic response can be highly dampened or enhanced. The explanation is sediment composed by multi-size particles can alternate states of mobilization or surface shielding and the transient behavior is inherently intertwined with the availability of mobile particles. We conclude that complex nonlinear dynamics of hydro-geomorphic processes are inherent expressions of physical interactions. As complete knowledge of watershed properties, states, or forcings will always present the ultimate, if ever resolvable, challenge, deterministic predictability will remain handicapped. Coupling of uncertainty quantification methods and space-time physics-based approaches will need to evolve to facilitate mechanistic interpretations and informed practical applications.

Corn stover harvest increases herbicide movement to subsurface drains - Root Zone Water Quality Model simulations.

PubMed

Shipitalo, Martin J; Malone, Robert W; Ma, Liwang; Nolan, Bernard T; Kanwar, Rameshwar S; Shaner, Dale L; Pederson, Carl H

2016-06-01

Crop residue removal for bioenergy production can alter soil hydrologic properties and the movement of agrochemicals to subsurface drains. The Root Zone Water Quality Model (RZWQM), previously calibrated using measured flow and atrazine concentrations in drainage from a 0.4 ha chisel-tilled plot, was used to investigate effects of 50 and 100% corn (Zea mays L.) stover harvest and the accompanying reductions in soil crust hydraulic conductivity and total macroporosity on transport of atrazine, metolachlor and metolachlor oxanilic acid (OXA). The model accurately simulated field-measured metolachlor transport in drainage. A 3 year simulation indicated that 50% residue removal reduced subsurface drainage by 31% and increased atrazine and metolachlor transport in drainage 4-5-fold when surface crust conductivity and macroporosity were reduced by 25%. Based on its measured sorption coefficient, approximately twofold reductions in OXA losses were simulated with residue removal. The RZWQM indicated that, if corn stover harvest reduces crust conductivity and soil macroporosity, losses of atrazine and metolachlor in subsurface drainage will increase owing to reduced sorption related to more water moving through fewer macropores. Losses of the metolachlor degradation product OXA will decrease as a result of the more rapid movement of the parent compound into the soil. Published 2015. This article is a U.S. Government work and is in the public domain in the USA. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Evaluation of the BioVapor Model

EPA Science Inventory

The BioVapor model addresses transport and biodegradation of petroleum vapors in the subsurface. This presentation describes basic background on the nature and scientific basis of environmental transport models. It then describes a series of parameter uncertainty runs of the Bi...

A new solar cycle model including meridional circulation

NASA Technical Reports Server (NTRS)

Wang, Y.-M.; Sheeley, N. R., Jr.; Nash, A. G.

1991-01-01

A kinematic model is presented for the solar cycle which includes not only the transport of magnetic flux by supergranular diffusion and a poleward bulk flow at the sun's surface, but also the effects of turbulent diffusion and an equatorward 'return flow' beneath the surface. As in the earlier models of Babcock and Leighton, the rotational shearing of a subsurface poloidal field generates toroidal flux that erupts at the surface in the form of bipolar magnetic regions. However, such eruptions do not result in any net loss of toroidal flux from the sun (as assumed by Babcock and Leighton); instead, the large-scale toroidal field is destroyed both by 'unwinding' as the local poloidal field reverses its polarity, and by diffusion as the toroidal flux is transported equatorward by the subsurface flow and merged with its opposite hemisphere counterpart. The inclusion of meridional circulation allows stable oscillations of the magnetic field, accompanied by the equatorward progression of flux eruptions, to be achieved even in the absence of a radial gradient in the angular velocity. An illustrative case in which a subsurface flow speed of order 1 m/s and subsurface diffusion rate of order 10 sq km/s yield 22-yr oscillations in qualitative agreement with observations.

Methane clathrate stability zone variations and gas transport in the Martian subsurface

NASA Astrophysics Data System (ADS)

Karatekin, O.; Gloesener, E.; Dehant, V. M. A.; Temel, O.

2016-12-01

During the last years, several detections of methane in the atmosphere of Mars were reported from Earth-based and Mars orbit instruments with abundances ranging to tens of parts-per-billion by volume (ppbv). Recently, the Curiosity rover detected methane with background levels of 0.7 ppbv and episodic releases of 7 ppbv. Although the methane sources are still unknown, this gas may have been stored in reservoirs of clathrate hydrate in the Martian subsurface where thermodynamics conditions are favourable to their presence. Clathrate hydrates are crystalline compounds constituted by cages formed by hydrogen-bonded water molecules inside of which guest gas molecules are trapped. In this study, methane clathrate stability in the Martian subsurface are investigated and their temporal and spatial variations are studied. Present-day maps of methane clathrate stability zone are produced by coupling the stability conditions of methane clathrate with a subsurface model using the available observations such as the the thermal inertia derived from TES MGS data. Then, a gas transport model has been used to study the methane flux at the surface due to the diffusion of different plausible methane volumes released by clathrate hydrates at variable depths under the Martian surface.

Subsurface damage in precision ground ULE(R) and Zerodur(R) surfaces.

PubMed

Tonnellier, X; Morantz, P; Shore, P; Baldwin, A; Evans, R; Walker, D D

2007-09-17

The total process cycle time for large ULE((R)) and Zerodur((R))optics can be improved using a precise and rapid grinding process, with low levels of surface waviness and subsurface damage. In this paper, the amounts of defects beneath ULE((R)) and Zerodur((R) )surfaces ground using a selected grinding mode were compared. The grinding response was characterised by measuring: surface roughness, surface profile and subsurface damage. The observed subsurface damage can be separated into two distinct depth zones, which are: 'process' and 'machine dynamics' related.

Earth Sciences Division

NASA Astrophysics Data System (ADS)

1991-06-01

This Annual Report presents summaries of selected representative research activities grouped according to the principal disciplines of the Earth Sciences Division: Reservoir Engineering and Hydrogeology, Geology and Geochemistry, and Geophysics and Geomechanics. Much of the Division's research deals with the physical and chemical properties and processes in the earth's crust, from the partially saturated, low-temperature near-surface environment to the high-temperature environments characteristic of regions where magmatic-hydrothermal processes are active. Strengths in laboratory and field instrumentation, numerical modeling, and in situ measurement allow study of the transport of mass and heat through geologic media -- studies that now include the appropriate chemical reactions and the hydraulic-mechanical complexities of fractured rock systems. Of particular note are three major Division efforts addressing problems in the discovery and recovery of petroleum, the application of isotope geochemistry to the study of geodynamic processes and earth history, and the development of borehole methods for high-resolution imaging of the subsurface using seismic and electromagnetic waves. In 1989, a major DOE-wide effort was launched in the areas of Environmental Restoration and Waste Management. Many of the methods previously developed for and applied to deeper regions of the earth will, in the coming years, be turned toward process definition and characterization of the very shallow subsurface, where man-induced contaminants now intrude and where remedial action is required.

Reactive transport modeling of subsurface arsenic removal systems in rural Bangladesh.

PubMed

Rahman, M M; Bakker, M; Patty, C H L; Hassan, Z; Röling, W F M; Ahmed, K M; van Breukelen, B M

2015-12-15

Subsurface Arsenic Removal (SAR) is a technique for in-situ removal of arsenic from groundwater. Extracted groundwater is aerated and re-injected into an anoxic aquifer, where the oxygen in the injected water reacts with ferrous iron in the aquifer to form hydrous ferric oxide (HFO). Subsequent extraction of groundwater contains temporarily lower As concentrations, because As sorbs onto the HFO. Injection, storage, and extraction together is called a cycle. A reactive transport model (RTM) was developed in PHREEQC to determine the hydrogeochemical processes responsible for As (im)mobilization during experimental SAR operation performed in Bangladesh. Oxidation of Fe(II) and As(III) were modeled using kinetic-rate expressions. Cation exchange, precipitation of HFO, and surface complexation, were modeled as equilibrium processes. A best set of surface complexation reactions and corresponding equilibrium constants was adopted from previous studies to simulate all 20 cycles of a SAR experiment. The model gives a reasonable match with observed concentrations of different elements in the extracted water (e.g., the r(2) value of As was 0.59 or higher). As concentrations in the extracted water are governed by four major processes. First, As concentration decreases in response to the elevated pH of injection water and likewise increases when native neutral pH groundwater flows in. Second, the sorption capacity for As increases due to the gradual buildup of HFO. Third, As sorption is enhanced by preferential removal of As(V). Fourth, competitive sorption of Si limits the capacity of freshly precipitated HFO for As sorption. Transferability of the developed reactive transport model was demonstrated through successful application of the model, without further calibration, to two additional SAR sites in Bangladesh. This gives confidence that the model could be useful to assess potential SAR performance at locations in Bangladesh based on local hydrogeochemical conditions. Copyright © 2015 Elsevier B.V. All rights reserved.

dfnWorks: A discrete fracture network framework for modeling subsurface flow and transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hyman, Jeffrey D.; Karra, Satish; Makedonska, Nataliia

DFNWORKS is a parallelized computational suite to generate three-dimensional discrete fracture networks (DFN) and simulate flow and transport. Developed at Los Alamos National Laboratory over the past five years, it has been used to study flow and transport in fractured media at scales ranging from millimeters to kilometers. The networks are created and meshed using DFNGEN, which combines FRAM (the feature rejection algorithm for meshing) methodology to stochastically generate three-dimensional DFNs with the LaGriT meshing toolbox to create a high-quality computational mesh representation. The representation produces a conforming Delaunay triangulation suitable for high performance computing finite volume solvers in anmore » intrinsically parallel fashion. Flow through the network is simulated in dfnFlow, which utilizes the massively parallel subsurface flow and reactive transport finite volume code PFLOTRAN. A Lagrangian approach to simulating transport through the DFN is adopted within DFNTRANS to determine pathlines and solute transport through the DFN. Example applications of this suite in the areas of nuclear waste repository science, hydraulic fracturing and CO 2 sequestration are also included.« less

dfnWorks: A discrete fracture network framework for modeling subsurface flow and transport

DOE PAGES

Hyman, Jeffrey D.; Karra, Satish; Makedonska, Nataliia; ...

2015-11-01

DFNWORKS is a parallelized computational suite to generate three-dimensional discrete fracture networks (DFN) and simulate flow and transport. Developed at Los Alamos National Laboratory over the past five years, it has been used to study flow and transport in fractured media at scales ranging from millimeters to kilometers. The networks are created and meshed using DFNGEN, which combines FRAM (the feature rejection algorithm for meshing) methodology to stochastically generate three-dimensional DFNs with the LaGriT meshing toolbox to create a high-quality computational mesh representation. The representation produces a conforming Delaunay triangulation suitable for high performance computing finite volume solvers in anmore » intrinsically parallel fashion. Flow through the network is simulated in dfnFlow, which utilizes the massively parallel subsurface flow and reactive transport finite volume code PFLOTRAN. A Lagrangian approach to simulating transport through the DFN is adopted within DFNTRANS to determine pathlines and solute transport through the DFN. Example applications of this suite in the areas of nuclear waste repository science, hydraulic fracturing and CO 2 sequestration are also included.« less

Subsurface energy storage and transport for solar-powered geysers on Triton

NASA Technical Reports Server (NTRS)

Kirk, Randolph L.; Soderblom, Laurence A.; Brown, Robert H.

1990-01-01

The location of active geyser-like eruptions and related features close to the current subsolar latitude on Triton suggests a solar energy source for these phenomena. Solid-state greenhouse calculations have shown that sunlight can generate substantially elevated subsurface temperatures. A variety of models for the storage of solar energy in a subgreenhouse layer and for the supply of gas and energy to a geyser are examined. 'Leaky greenhouse' models with only vertical gas transport are inconsistent with the observed upper limit on geyser radius of about 1.5 km. However, lateral transport of energy by gas flow in a porous N2 layer with a block size on the order of a meter can supply the required amount of gas to a source region about 1 km in radius. The decline of gas output to steady state may occur over a period comparable with the inferred active geyser lifetime of 5 earth years. The required subsurface permeability may be maintained by thermal fracturing of the residual N2 polar cap. A lower limit on geyser source radius of about 50 to 100 m predicted by a theory of negatively buoyant jets is not readily attained.

Subsurface transport of orthophosphate in five agricultural watersheds, USA

USGS Publications Warehouse

Domagalski, Joseph L.; Johnson, Henry M.

2011-01-01

Concentrations of dissolved orthophosphate (ortho P) in the unsaturated zone, groundwater, tile drains, and groundwater/stream water interfaces were assessed in five agricultural watersheds to determine the potential for subsurface transport. Concentrations of iron oxides were measured in the aquifer material and adsorption of ortho P on oxide surfaces was assessed by geochemical modeling. Attenuation of ortho P in these aquifers was attributed primarily to sorption onto iron oxides, and in one location onto clay minerals. Only one location showed a clear indication of phosphorus transport to a stream from groundwater discharge, although groundwater did contribute to the stream load elsewhere. Subsurface ortho P movement at a site in California resulted in a plume down gradient from orchards, which was attenuated by a 200 m thick riparian zone with natural vegetation. Iron oxides had an effect on phosphorus movement and concentrations at all locations, and groundwater chemistry, especially pH, exerted a major control on the amount of phosphorus adsorbed. Groundwater pH at a site in Maryland was below 5 and that resulted in complete sequestration of phosphorus and no movement toward the stream. Geochemical modeling indicated that as the surfaces approached saturation, groundwater concentrations of ortho P rise rapidly.

Exploration criteria for low permeability geothermal resources. Final report. [Coso KGRA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Norton, D.

1977-10-01

Low permeability geothermal systems related to high temperature plutons in the upper crust were analyzed in order to ascertain those characteristics of these systems which could be detected by surface and shallow subsurface exploration methods. Analyses were designed to integrate data and concepts from the literature, which relate to the transport processes, together with computer simulation of idealized systems. The systems were analyzed by systematically varying input parameters in order to understand their effect on the variables which might be measured in an exploration-assessment program. The methods were applied to a prospective system in its early stages of evaluation. Datamore » from the Coso system were used. The study represents a first-order approximation to transport processes in geothermal systems, which consist of high temperature intrusions, host rock, and fluids. Included in an appendix are operations procedures for interactive graphics programs developed during the study. (MHR)« less

The role of the hyporheic flow on sediment transport processes : an experimental approach using particle image velocimetry

NASA Astrophysics Data System (ADS)

Rousseau, Gauthier; Sklivaniti, Angeliki; Vito Papa, Daniel; Ancey, Christophe

2017-04-01

The study of river dynamics usually considers a turbulent stream on an impervious bed. However, it is known that part of the total discharge takes place through the erodible bed, especially for mountain rivers. This hyporheic flow (or subsurface flow) is likely to play an active role in the stability of the erodible bed. The question then arises: How does the hyporheic flow affect bed stability and thereby bed load transport? Monitoring hyporheic flow under natural conditions remains a key challenge. Laboratory experiments and new measurement techniques shed new light on this problem. Using PIV-LIF method (Particle Image Velocimetry - Laser Induced Fluorescence) we investigate hyporheic flows through erodible beds. The experiment is conducted in a 2-m-long and 6-cm-width flume with 2-mm-diameter glass beads and 4-mm-diameter natural pebbles under turbulent stream conditions. In parallel, we develop a simple analytical model that accounts for the interaction between the surface and subsurface flows at the bed interface. As the Reynolds number of the hyporheic flow is fairly high (10 to 100), inertia cannot be neglected. This leads us to use the Darcy-Forchheimer law instead of Darcy's law to model hyporheic flows. We show that this model is consistent with the PIV-LIF experimental results. Moreover, the PIV-LIF data show that hyporheic flows modify the velocity profile and turbulence. Our measurements and empirical model emphasize the exchange processes in coarse-grained river for incipient sediment motion.

Project Work Plan: Sequestration of Strontium-90 Subsurface Contamination in the Hanford 100-N Area by Surface Infiltration of an Apatite Solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szecsody, Jim E.

2006-04-30

We propose to develop an infiltration strategy that defines the precipitation rate of an apatite-forming solution and Sr-90 sequestration processes under variably saturated (low water content) conditions. We will develop this understanding through small-scale column studies, intermediate-scale two-dimensional (2-D) experiments, and numerical modeling to quantify individual and coupled processes associated with apatite formation and Sr-90 transport during and after infiltration of the Ca-citrate-PO4 solution. Development of capabilities to simulate these coupled biogeochemical processes during both injection and infiltration will be used to determine the most cost-effective means to emplace an in situ apatite barrier with a longevity of 300 yearsmore » to permanently sequester Sr-90 until it decays. Biogeochemical processes that will be investigated are citrate biodegradation and apatite precipitation rates at varying water contents as a function of water content. Coupled processes that will be investigated include the influence of apatite precipitation (which occupies pore space) on the hydraulic and transport properties of the porous media during infiltration.« less

BACTERIAL TRANSPORT THROUGH HOMOGENEOUS SOIL

EPA Science Inventory

The transport of microorganisms in soils is of major importance for bioremediation of subsurface polluted zones and for pollution of groundwater with pathogens. A procedure for evaluating the relative mobility and recovery of bacteria in the soil matrix was developed. In the meth...

USING SUBSURFACE TRANSPORT RESEARCH TO ACHIEVE AGENCY OUTCOMES

EPA Science Inventory

Gasoline leaks from underground storage tanks can cause ground water contamination because there are a number of organic chemicals in gasoline. These chemicals have varying properties that influence how far contamination extends from the release. Research on transport of these ...

BioVapor Model Evaluation (St. Louis, MO)

EPA Science Inventory

The BioVapor model addresses transport and biodegradation of petroleum vapors in the subsurface. This presentation describes basic background on the nature and scientific basis of environmental transport models. It then describes a series of parameter uncertainty runs of the Bi...

SELECTION AND CALIBRATION OF SUBSURFACE REACTIVE TRANSPORT MODELS USING A SURROGATE-MODEL APPROACH

EPA Science Inventory

While standard techniques for uncertainty analysis have been successfully applied to groundwater flow models, extension to reactive transport is frustrated by numerous difficulties, including excessive computational burden and parameter non-uniqueness. This research introduces a...

APPROXIMATE MULTIPHASE FLOW MODELING BY CHARACTERISTIC METHODS

EPA Science Inventory

The flow of petroleum hydrocarbons, organic solvents and other liquids that are immiscible with water presents the nation with some of the most difficult subsurface remediation problems. One aspect of contaminant transport associated releases of such liquids is the transport as a...

Effects of cell surface characteristics and manure-application practices on Escherichia coli populations in the subsurface: A three-farm study

NASA Astrophysics Data System (ADS)

Salvucci, A. E.; Elton, M.; Siler, J. D.; Zhang, W.; Richards, B. K.; Geohring, L. D.; Warnick, L. D.; Hay, A. G.; Steenhuis, T.

2010-12-01

The introduction of microbial pathogens into the environment from untreated manure represents a threat to water quality and human health. Thus, understanding the effect of manure management strategies is imperative to effectively mitigate the inadvertent release of pathogens, particularly in subsurface environments where they can be transported through macropores to the groundwater or through agricultural tile line to open water bodies. The production of cell-surface biomolecules is also suspected to play an important role in the environmental survival and transport of enterobacterial pathogens. This study collected Escherichia coli samples from three dairy farms with artificial tile drainage systems and active manure spreading in the Central New York region over a three-month period. Sampling targeted four potential source locations on each farm: (i) cow housing, (ii) manure storage facilities, (iii) field soil, and (iv) subsurface drainage effluent. Over 2800 E. coli isolates were recovered and consequently analyzed for the cell surface components, cellulose and curli, traits associated with increased environmental survival, altered transport and pathogenicity. The E. coli isolates from locations i-iii displayed highly variable curli and cellulose-producing communities, while isolates collected from subsurface runoff on each farm had stable curli and cellulose production communities over all sampling dates. Furthermore, the method of manure application to the fields influenced the population characteristics found in drainage effluent isolates. Incorporation of manure into the soil was correlated to isolate populations largely deficient of curli and cellulose; whereas farms that only surface-applied manure were correlated to isolate populations of high curli and cellulose production. The production of curli and cellulose has previously been shown to be a response to environmental stress on the cell. Therefore, incorporation of manure directly into the soil appears to minimize environmental stresses, like UV radiation, desiccation and temperature fluctuation, typically found on the soil surface. Our findings indicate that E. coli strains above the surface are largely diverse, until they enter subsurface environments where specific extracellular characteristics are likely advantageous for survival and/or transport.

Viscous and gravitational contributions to mixing during vertical brine transport in water-saturated porous media

PubMed Central

Flowers, Tracey C.; Hunt, James R.

2010-01-01

The transport of fluids miscible with water arises in groundwater contamination and during remediation of the subsurface environment. For concentrated salt solutions, i.e., brines, the increased density and viscosity determine mixing processes between these fluids and ambient groundwater. Under downward flow conditions, gravitational and viscous forces work against each other to determine the interfacial mixing processes. Historically, mixing has been modeled as a dispersive process, as viscous fingering, and as a combination of both using approaches that were both analytical and numerical. A compilation of previously reported experimental data on vertical miscible displacements by fluids with significant density and viscosity contrasts reveals some agreement with a stability analysis presented by Hill (1952). Additional experimental data on one-dimensional dispersion during downward displacement of concentrated salt solutions by freshwater and freshwater displacement by brines support the stability analysis and provides an empirical representation for dispersion coefficients as functions of a gravity number and a mobility ratio. PMID:20300476

TReacLab: An object-oriented implementation of non-intrusive splitting methods to couple independent transport and geochemical software

NASA Astrophysics Data System (ADS)

Jara, Daniel; de Dreuzy, Jean-Raynald; Cochepin, Benoit

2017-12-01

Reactive transport modeling contributes to understand geophysical and geochemical processes in subsurface environments. Operator splitting methods have been proposed as non-intrusive coupling techniques that optimize the use of existing chemistry and transport codes. In this spirit, we propose a coupler relying on external geochemical and transport codes with appropriate operator segmentation that enables possible developments of additional splitting methods. We provide an object-oriented implementation in TReacLab developed in the MATLAB environment in a free open source frame with an accessible repository. TReacLab contains classical coupling methods, template interfaces and calling functions for two classical transport and reactive software (PHREEQC and COMSOL). It is tested on four classical benchmarks with homogeneous and heterogeneous reactions at equilibrium or kinetically-controlled. We show that full decoupling to the implementation level has a cost in terms of accuracy compared to more integrated and optimized codes. Use of non-intrusive implementations like TReacLab are still justified for coupling independent transport and chemical software at a minimal development effort but should be systematically and carefully assessed.

Community Characterization of Microbial Populations Found at a Cold Water Sulfidic Spring in the Canadian High Arctic

NASA Astrophysics Data System (ADS)

Trivedi, C.; Lau, G. E.; Templeton, A. S.; Grasby, S. E.; Spear, J. R.

2015-12-01

The unique environment on Europa makes it an ideal target for astrobiological investigation. One such earth-based analogue to aid in this investigation is the sulfur-dominated glacial spring system found at Borup Fiord Pass (BFP), Ellesmere Island, Nunavut, Canada. In this system, subsurface microbial sulfate reduction produces hydrogen sulfide, which is transported through the glacier along spring channels [1]. As the surface oxidation of H2S occurs, resultant deposition of elemental sulfur (S0) and other minerals becomes visible (attached image). The energy released from these reactions can support potential microbial metabolisms and may be a valuable representation of microbial processes occurring on Europa. The resulting sulfur minerals provide sensitive records of dynamic atmospheric, geological, hydrological, chemical, and biological processes on planetary surfaces. Moreover, we expect that the S0-rich deposits of this glacial spring system will serve as a mineralogical record for biological activity and will provide a valuable tool for recognizing potential sulfur-based life on Europa. During a recent collaborative expedition (2014) to BFP, samples were taken from the toe of the glacier in an area called the 'Blister Crust' (attached image). At this location, glacial channels reach the surface, representing an active interface between subsurface and surface processes. Initial geochemical characterization at the site revealed high amounts of aqueous sulfide (1.8 mM) and hydrogen (29 nM), which likely serve as the electron donation potential in the system. Furthermore, preliminary 16S rRNA gene sequencing has shown a high abundance of the genus Sulfurimonas, which is a known sulfur metabolizer. Our research seeks to further characterize microbial communities found at this interface in order to elucidate information regarding in situ sulfur cycling and the potential to tie this into subsurface/surface processes on Europa. Continued work will provide guidance into potential astrobiological targets on the surface of Europa, predominantly in regions where subsurface fluids interact with surface icings. References: [1] Grasby S. E. et al. (2003) Astrobiology, 3(3), 583-596.

Sampling surface and subsurface particle-size distributions in wadable gravel-and cobble-bed streams for analyses in sediment transport, hydraulics, and streambed monitoring

Treesearch

Kristin Bunte; Steven R. Abt

2001-01-01

This document provides guidance for sampling surface and subsurface sediment from wadable gravel-and cobble-bed streams. After a short introduction to streams types and classifications in gravel-bed rivers, the document explains the field and laboratory measurement of particle sizes and the statistical analysis of particle-size distributions. Analysis of particle...

A 3D object-based model to simulate highly-heterogeneous, coarse, braided river deposits

NASA Astrophysics Data System (ADS)

Huber, E.; Huggenberger, P.; Caers, J.

2016-12-01

There is a critical need in hydrogeological modeling for geologically more realistic representation of the subsurface. Indeed, widely-used representations of the subsurface heterogeneity based on smooth basis functions such as cokriging or the pilot-point approach fail at reproducing the connectivity of high permeable geological structures that control subsurface solute transport. To realistically model the connectivity of high permeable structures of coarse, braided river deposits, multiple-point statistics and object-based models are promising alternatives. We therefore propose a new object-based model that, according to a sedimentological model, mimics the dominant processes of floodplain dynamics. Contrarily to existing models, this object-based model possesses the following properties: (1) it is consistent with field observations (outcrops, ground-penetrating radar data, etc.), (2) it allows different sedimentological dynamics to be modeled that result in different subsurface heterogeneity patterns, (3) it is light in memory and computationally fast, and (4) it can be conditioned to geophysical data. In this model, the main sedimentological elements (scour fills with open-framework-bimodal gravel cross-beds, gravel sheet deposits, open-framework and sand lenses) and their internal structures are described by geometrical objects. Several spatial distributions are proposed that allow to simulate the horizontal position of the objects on the floodplain as well as the net rate of sediment deposition. The model is grid-independent and any vertical section can be computed algebraically. Furthermore, model realizations can serve as training images for multiple-point statistics. The significance of this model is shown by its impact on the subsurface flow distribution that strongly depends on the sedimentological dynamics modeled. The code will be provided as a free and open-source R-package.

Imaging Preferential Flow Pathways of Contaminants from Passive Acid Mine Drainage Mitigation Sites Using Electrical Resistivity

NASA Astrophysics Data System (ADS)

Kelley, N.; Mount, G.; Terry, N.; Herndon, E.; Singer, D. M.

2017-12-01

The Critical Zone represents the surficial and shallow layer of rock, air, water, and soil where most interactions between living organisms and the Earth occur. Acid mine drainage (AMD) resulting from coal extraction can influence both biological and geochemical processes across this zone. Conservative estimates suggest that more than 300 million gallons of AMD are released daily, making this acidic solution of water and contaminants a common issue in areas with legacy or current coal extraction. Electrical resistivity imaging (ERI) provides a rapid and minimally invasive method to identify and monitor contaminant pathways from AMD remediation systems in the subsurface of the Critical Zone. The technique yields spatially continuous data of subsurface resistivity that can be inverted to determine electrical conductivity as a function of depth. Since elevated concentrations of heavy metals can directly influence soil conductivity, ERI data can be used to trace the flow pathways or perhaps unknown mine conduits and transport of heavy metals through the subsurface near acid mine drainage sources. This study aims to examine preferential contaminant migration from those sources through substrate pores, fractures, and shallow mine workings in the near subsurface surrounding AMD sites in eastern Ohio and western Pennsylvania. We utilize time lapse ERI measures during different hydrologic conditions to better understand the variability of preferential flow pathways in relation to changes in stage and discharge within the remediation systems. To confirm ERI findings, and provide constraint to geochemical reactions occurring in the shallow subsurface, we conducted Inductively Coupled Plasma (ICP) spectrometry analysis of groundwater samples from boreholes along the survey transects. Through these combined methods, we can provide insight into the ability of engineered systems to contain and isolate metals in passive acid mine drainage treatment systems.

Hydrologic response of catchments to precipitation: Quantification of mechanical carriers and origins of water

NASA Astrophysics Data System (ADS)

Park, Y.-J.; Sudicky, E. A.; Brookfield, A. E.; Jones, J. P.

2011-12-01

Precipitation-induced overland and groundwater flow and mixing processes are quantified to analyze the temporal (event and pre-event water) and spatial (groundwater discharge and overland runoff) origins of water entering a stream. Using a distributed-parameter control volume finite-element simulator that can simultaneously solve the fully coupled partial differential equations describing 2-D Manning and 3-D Darcian flow and advective-dispersive transport, mechanical flow (driven by hydraulic potential) and tracer-based hydrograph separation (driven by dispersive mixing as well as mechanical flow) are simulated in response to precipitation events in two cross sections oriented parallel and perpendicular to a stream. The results indicate that as precipitation becomes more intense, the subsurface mechanical flow contributions tend to become less significant relative to the total pre-event stream discharge. Hydrodynamic mixing can play an important role in enhancing pre-event tracer signals in the stream. This implies that temporally tagged chemical signals introduced into surface-subsurface flow systems from precipitation may not be strong enough to detect the changes in the subsurface flow system. It is concluded that diffusive/dispersive mixing, capillary fringe groundwater ridging, and macropore flow can influence the temporal sources of water in the stream, but any sole mechanism may not fully explain the strong pre-event water discharge. Further investigations of the influence of heterogeneity, residence time, geomorphology, and root zone processes are required to confirm the conclusions of this study.

Hydrologic response of catchments to precipitation: Quantification of mechanical carriers and origins of water

USGS Publications Warehouse

Park, Y.-J.; Sudicky, E.A.; Brookfield, A.E.; Jones, J.P.

2011-01-01

Precipitation-induced overland and groundwater flow and mixing processes are quantified to analyze the temporal (event and pre-event water) and spatial (groundwater discharge and overland runoff) origins of water entering a stream. Using a distributed-parameter control volume finite-element simulator that can simultaneously solve the fully coupled partial differential equations describing 2-D Manning and 3-D Darcian flow and advective-dispersive transport, mechanical flow (driven by hydraulic potential) and tracer-based hydrograph separation (driven by dispersive mixing as well as mechanical flow) are simulated in response to precipitation events in two cross sections oriented parallel and perpendicular to a stream. The results indicate that as precipitation becomes more intense, the subsurface mechanical flow contributions tend to become less significant relative to the total pre-event stream discharge. Hydrodynamic mixing can play an important role in enhancing pre-event tracer signals in the stream. This implies that temporally tagged chemical signals introduced into surface-subsurface flow systems from precipitation may not be strong enough to detect the changes in the subsurface flow system. It is concluded that diffusive/dispersive mixing, capillary fringe groundwater ridging, and macropore flow can influence the temporal sources of water in the stream, but any sole mechanism may not fully explain the strong pre-event water discharge. Further investigations of the influence of heterogeneity, residence time, geomorphology, and root zone processes are required to confirm the conclusions of this study. Copyright 2011 by the American Geophysical Union.

VIRTUS: A MODEL OF VIRUS TRANSPORT IN UNSATURATED SOILS

EPA Science Inventory

As a result of the recently proposed mandatory groundwater disinfection requirements to inactivate viruses in potable water supplies, there has been increasing interest in virus fate and transport in the subsurface. Several models have been developed to predict the fate of viruse...

Sedimentary silicon isotope indicates the Kuroshio subsurface upwelling in the East China Sea

NASA Astrophysics Data System (ADS)

Zhao, Y.; Yang, S.; Su, N.

2017-12-01

The Kuroshio as the western boundary current of the North Pacific subtropical circulation, originates from east of the Philippine Islands, and flows northeastward along the eastern coast of Taiwan. It's subsurface water intrudes the East China Sea (ECS) and forms a typical upwelling on the inner shelf, which may play an important role in the material and heat transport, biogeochemical process and marine ecosystem of the ECS.To date, most previous studies on the Kuroshio subsurface upwelling focuse on the seasonal and interannual variations, and few researches touch on the upwelling evolution in the geologic past. In this study, eight short sediment cores were taken along the ECS inner shelf (upwelling area), which allow us to reconstruct the upwelling history over the last several hundred years. Although conventional indexes of oceanographic changes, such as salinity, temperature and hydrogen and oxygen isotope, provide valuable constraints on the modern oceanic circulation and water mass movements, how to reconstruct them from geologic records is always a challenging work. In this contribution, we present the data of stable silicon isotope, biogenic opal, diatom assemblages, element geochemistry and stable carbon and nitrogen isotopes of these core sediments, and aim to decipher the Kuroshio subsurface upwelling history on the ECS shelf. We will also illustrate the difference in δ30Si signals between small (<30 um) and large (>150 um) diatom fractions, and test whether it is an effective indicator for paleo-upwelling intensity.

Scale-Dependent Solute Dispersion in Variably Saturated Porous Media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rockhold, Mark L.; Zhang, Z. F.; Bott, Yi-Ju

2016-03-29

This work was performed to support performance assessment (PA) calculations for the Integrated Disposal Facility (IDF) at the Hanford Site. PA calculations require defensible estimates of physical, hydraulic, and transport parameters to simulate subsurface water flow and contaminant transport in both the near- and far-field environments. Dispersivity is one of the required transport parameters.

Nonlinear dynamics in flow through unsaturated fractured-porous media: Status and perspectives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faybishenko, Boris

2002-11-27

The need has long been recognized to improve predictions of flow and transport in partially saturated heterogeneous soils and fractured rock of the vadose zone for many practical applications, such as remediation of contaminated sites, nuclear waste disposal in geological formations, and climate predictions. Until recently, flow and transport processes in heterogeneous subsurface media with oscillating irregularities were assumed to be random and were not analyzed using methods of nonlinear dynamics. The goals of this paper are to review the theoretical concepts, present the results, and provide perspectives on investigations of flow and transport in unsaturated heterogeneous soils and fracturedmore » rock, using the methods of nonlinear dynamics and deterministic chaos. The results of laboratory and field investigations indicate that the nonlinear dynamics of flow and transport processes in unsaturated soils and fractured rocks arise from the dynamic feedback and competition between various nonlinear physical processes along with complex geometry of flow paths. Although direct measurements of variables characterizing the individual flow processes are not technically feasible, their cumulative effect can be characterized by analyzing time series data using the models and methods of nonlinear dynamics and chaos. Identifying flow through soil or rock as a nonlinear dynamical system is important for developing appropriate short- and long-time predictive models, evaluating prediction uncertainty, assessing the spatial distribution of flow characteristics from time series data, and improving chemical transport simulations. Inferring the nature of flow processes through the methods of nonlinear dynamics could become widely used in different areas of the earth sciences.« less

Modelling coupled microbial processes in the subsurface: Model development, verification, evaluation and application

NASA Astrophysics Data System (ADS)

Masum, Shakil A.; Thomas, Hywel R.

2018-06-01

To study subsurface microbial processes, a coupled model which has been developed within a Thermal-Hydraulic-Chemical-Mechanical (THCM) framework is presented. The work presented here, focuses on microbial transport, growth and decay mechanisms under the influence of multiphase flow and bio-geochemical reactions. In this paper, theoretical formulations and numerical implementations of the microbial model are presented. The model has been verified and also evaluated against relevant experimental results. Simulated results show that the microbial processes have been accurately implemented and their impacts on porous media properties can be predicted either qualitatively or quantitatively or both. The model has been applied to investigate biofilm growth in a sandstone core that is subjected to a two-phase flow and variable pH conditions. The results indicate that biofilm growth (if not limited by substrates) in a multiphase system largely depends on the hydraulic properties of the medium. When the change in porewater pH which occurred due to dissolution of carbon dioxide gas is considered, growth processes are affected. For the given parameter regime, it has been shown that the net biofilm growth is favoured by higher pH; whilst the processes are considerably retarded at lower pH values. The capabilities of the model to predict microbial respiration in a fully coupled multiphase flow condition and microbial fermentation leading to production of a gas phase are also demonstrated.

Diffusional Transport of Organic Solutes in Subsurface Clay Lenses and Layers

NASA Astrophysics Data System (ADS)

Demond, A. H.; Ayral, D.; Goltz, M. N.

2009-12-01

The storage of organic solvents in clay lenses and layers in the subsurface creates long-term contaminant sources. Because of the low hydraulic conductivities of clay, it is thought that organic movement into clay lenses occurs through the process of diffusion. The ratio of the effective diffusion coefficient in the porous medium and the diffusion coefficient in bulk water is usually given by the tortuosity factor which accounts for the reduced area and the increased path length in the porous medium. However, there is field evidence which suggests that the concentrations in these lenses exceed that which can be accounted for by simple diffusion. There are reports, for example, of tortuosity factors greater than 1.0, which theoretically is not possible. Clays such as montmorillonite or bentonite shrink and swell depending on water content, and similar behavior can occur in the presence of organic solvents. In fact, research has shown that the basal spacing of bentonite can decrease by 50% when permeated with heptane. Such contraction of the clay structure can lead to the formation of cracks and macropores, with a concomitant alteration of the diffusional pathways that solutes follow. Models formulated for diffusional transport in soil are available to calculate the tortuosity factor as a function of water content. In addition, models are available to simulate phenomena in which the diffusion coefficient is concentration dependent. However, calculations of diffusional transport using such models show that they may not adequately reflect the impact of the alteration of the clay structure. However, modeling the transport of organic solutes in clay as a dual-domain system with some minimal advective transport in macropores can yield tortuosity factors greater than 1.0. Thus, it appears the cracking of clay in contact with organic solvents and a resultant advective component to transport of the solute may be an explanation of field observations.

Correcting for diffusion in carbon-14 dating of ground water

USGS Publications Warehouse

Sanford, W.E.

1997-01-01

It has generally been recognized that molecular diffusion can be a significant process affecting the transport of carbon-14 in the subsurface when occurring either from a permeable aquifer into a confining layer or from a fracture into a rock matrix. An analytical solution that is valid for steady-state radionuclide transport through fractured rock is shown to be applicable to many multilayered aquifer systems. By plotting the ratio of the rate of diffusion to the rate of decay of carbon-14 over the length scales representative of several common hydrogeologic settings, it is demonstrated that diffusion of carbon-14 should often be not only a significant process, but a dominant one relative to decay. An age-correction formula is developed and applied to the Bangkok Basin of Thailand, where a mean carbon-14-based age of 21,000 years was adjusted to 11,000 years to account for diffusion. This formula and its graphical representation should prove useful for many studies, for they can be used first to estimate the potential role of diffusion and then to make a simple first-order age correction if necessary.It has generally been recognized that molecular diffusion can be a significant process affecting the transport of carbon-14 in the subsurface when occurring either from a permeable aquifer into a confining layer or from a fracture into a rock matrix. An analytical solution that is valid for steady-state radionuclide transport through fractured rock is shown to be applicable to many multilayered aquifer systems. By plotting the ratio of the rate of diffusion to the rate of decay of carbon-14 over the length scales representative of several common hydrogeologic settings, it is demonstrated that diffusion of carbon-14 should often be not only a significant process, but a dominant one relative to decay. An age-correction formula is developed and applied to the Bangkok Basin of Thailand, where a mean carbon-14-based age of 21,000 years was adjusted to 11,000 years to account for diffusion. This formula and its graphical representation should prove useful for many studies, for they can be used first to estimate the potential role of diffusion and then to make a simple first-order age correction if necessary.

Influence of Reactive Transport on the Reduction of U(VI) in the Presence of Fe(III) and Nitrate: Implications for U(VI) Immobilization by Bioremediation / Biobarriers- Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

B.D. Wood

2007-01-01

Subsurface contamination by metals and radionuclides represent some of the most challenging remediation problems confronting the Department of Energy (DOE) complex. In situ remediation of these contaminants by dissimilatory metal reducing bacteria (DMRB) has been proposed as a potential cost effective remediation strategy. The primary focus of this research is to determine the mechanisms by which the fluxes of electron acceptors, electron donors, and other species can be controlled to maximize the transfer of reductive equivalents to the aqueous and solid phases. The proposed research is unique in the NABIR portfolio in that it focuses on (i) the role ofmore » flow and transport in the initiation of biostimulation and the successful sequestration of metals and radionuclides [specifically U(VI)], (ii) the subsequent reductive capacity and stability of the reduced sediments produced by the biostimulation process, and (iii) the potential for altering the growth of biomass in the subsurface by the addition of specific metabolic uncoupling compounds. A scientifically-based understanding of these phenomena are critical to the ability to design successful bioremediation schemes. The laboratory research will employ Shewanella putrefaciens (CN32), a facultative DMRB that can use Fe(III) oxides as a terminal electron acceptor. Sediment-packed columns will be inoculated with this organism, and the reduction of U(VI) by the DMRB will be stimulated by the addition of a carbon and energy source in the presence of Fe(III). Separate column experiments will be conducted to independently examine: (1) the importance of the abiotic reduction of U(VI) by biogenic Fe(II); (2) the influence of the transport process on Fe(III) reduction and U(VI) immobilization, with emphasis on methods for controlling the fluxes of aqueous species to maximize uranium reduction; (3) the reductive capacity of biologically-reduced sediments (with respect to re-oxidation by convective fluxes of O2 and NO3-) and the long-term stability of immobilized uranium mineral phases after bioremediation processes are complete, and (4) the ability for metabolic uncoupling compounds to maintain microbial growth while limiting biomass production. The results of the laboratory experiments will be used to develop mathematical descriptive models for the coupled transport and reduction processes.« less

Examining Changes in Radioxenon Isotope Activity Ratios during Subsurface Transport

NASA Astrophysics Data System (ADS)

Annewandter, Robert

2014-05-01

The Non-Proliferation Experiment (NPE) has demonstrated and modelled the usefulness of barometric pumping induced gas transport and subsequent soil gas sampling during On-Site inspections. Generally, gas transport has been widely studied with different numerical codes. However, gas transport of radioxenons and radioiodines in the post-detonation regime and their possible fractionation is still neglected in the open peer-reviewed literature. Atmospheric concentrations of the radioxenons Xe-135, Xe-133m, Xe-133 and Xe-131m can be used to discriminate between civilian releases (nuclear power plants or medical isotope facilities), and nuclear explosion sources. It is based on the multiple isotopic activity ratio method. Yet it is not clear whether subsurface migration of the radionuclides, with eventual release into the atmosphere, can affect the activity ratios due to fractionation. Fractionation can be caused by different mass diffusivities due to mass differences between the radionuclides. Cyclical changes in atmospheric pressure can drive subsurface gas transport. This barometric pumping phenomenon causes an oscillatoric flow in upward trending fractures or highly conductive faults which, combined with diffusion into the porous matrix, leads to a net transport of gaseous components - a so-called ratcheting effect. We use a general purpose reservoir simulator (Complex System Modelling Platform, CSMP++) which is recognized by the oil industry as leading in Discrete Fracture-Matrix (DFM) simulations. It has been applied in a range of fields such as deep geothermal systems, three-phase black oil simulations, fracture propagation in fractured, porous media, and Navier-Stokes pore-scale modelling among others. It is specifically designed to account for structurally complex geologic situation of fractured, porous media. Parabolic differential equations are solved by a continuous Galerkin finite-element method, hyperbolic differential equations by a complementary finite volume method. The parabolic and hyperbolic problem can be solved separately by operator-splitting. The resulting system of linear equations is solved by the algebraic multigrid library SAMG, developed at the Fraunhofer Institute for Algorithms and Scientific Computing, Germany. CSMP++ is developed at Montan University of Leoben, ETH Zuerich, Imperial College London and Heriot-Watt University in Edinburgh. This study examines barometric pumping-driven subsurface transport of Xe-135, Xe-133m, Xe-133, Xe-131m including I-131, I-133 and I-135 on arrival times and isotopic activity ratios. This work was funded by the CTBTO Research Award for Young Scientist and Engineers (2013).

A multiple-point geostatistical method for characterizing uncertainty of subsurface alluvial units and its effects on flow and transport

USGS Publications Warehouse

Cronkite-Ratcliff, C.; Phelps, G.A.; Boucher, A.

2012-01-01

This report provides a proof-of-concept to demonstrate the potential application of multiple-point geostatistics for characterizing geologic heterogeneity and its effect on flow and transport simulation. The study presented in this report is the result of collaboration between the U.S. Geological Survey (USGS) and Stanford University. This collaboration focused on improving the characterization of alluvial deposits by incorporating prior knowledge of geologic structure and estimating the uncertainty of the modeled geologic units. In this study, geologic heterogeneity of alluvial units is characterized as a set of stochastic realizations, and uncertainty is indicated by variability in the results of flow and transport simulations for this set of realizations. This approach is tested on a hypothetical geologic scenario developed using data from the alluvial deposits in Yucca Flat, Nevada. Yucca Flat was chosen as a data source for this test case because it includes both complex geologic and hydrologic characteristics and also contains a substantial amount of both surface and subsurface geologic data. Multiple-point geostatistics is used to model geologic heterogeneity in the subsurface. A three-dimensional (3D) model of spatial variability is developed by integrating alluvial units mapped at the surface with vertical drill-hole data. The SNESIM (Single Normal Equation Simulation) algorithm is used to represent geologic heterogeneity stochastically by generating 20 realizations, each of which represents an equally probable geologic scenario. A 3D numerical model is used to simulate groundwater flow and contaminant transport for each realization, producing a distribution of flow and transport responses to the geologic heterogeneity. From this distribution of flow and transport responses, the frequency of exceeding a given contaminant concentration threshold can be used as an indicator of uncertainty about the location of the contaminant plume boundary.

Subsurface North Atlantic warming as a trigger of rapid cooling events: evidences from the Early Pleistocene (MIS 31-19)

NASA Astrophysics Data System (ADS)

Hernández-Almeida, I.; Sierro, F.-J.; Cacho, I.; Flores, J.-A.

2014-10-01

Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt IRD events during cold periods of the Early Pleistocene. We used Mg / Ca-based temperatures of deep-dwelling (Neogloboquadrina pachyderma sinistral) planktonic foraminifera and paired Mg / Ca-δ18O measurements to estimate the subsurface temperatures and δ18O of seawater at Site U1314. Carbon isotopes on benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and δ18O of seawater suggest increased temperatures and salinities during ice-rafting, likely due to enhanced northward subsurface transport of subtropical waters during periods of AMOC reduction. Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of ice-rafted detritus (IRD). Warm waters accumulated at subsurface would result in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. Release of heat and salt stored at subsurface would help to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during the MIS3.

Subsurface North Atlantic warming as a trigger of rapid cooling events: evidence from the early Pleistocene (MIS 31-19)

NASA Astrophysics Data System (ADS)

Hernández-Almeida, I.; Sierro, F.-J.; Cacho, I.; Flores, J.-A.

2015-04-01

Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt ice-rafted detritus (IRD) events during cold periods of the early Pleistocene. We used paired Mg / Ca and δ18O measurements of Neogloboquadrina pachyderma (sinistral - sin.), deep-dwelling planktonic foraminifera, to estimate the subsurface temperatures and seawater δ18O from a sediment core from Gardar Drift, in the subpolar North Atlantic. Carbon isotopes of benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and seawater δ18O suggest increased subsurface temperatures and salinities during ice-rafting, likely due to northward subsurface transport of subtropical waters during periods of weaker Atlantic Meridional Overturning Circulation (AMOC). Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of IRD. Subsurface accumulation of warm waters would have resulted in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. The release of heat stored at the subsurface to the atmosphere would have helped to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during Marine Isotope Stage (MIS) 3.

Exchange of Groundwater and Surface-Water Mediated by Permafrost Response to Seasonal and Long Term Air Temperature Variation

USGS Publications Warehouse

Ge, Shemin; McKenzie, Jeffrey; Voss, Clifford; Wu, Qingbai

2011-01-01

Permafrost dynamics impact hydrologic cycle processes by promoting or impeding groundwater and surface water exchange. Under seasonal and decadal air temperature variations, permafrost temperature changes control the exchanges between groundwater and surface water. A coupled heat transport and groundwater flow model, SUTRA, was modified to simulate groundwater flow and heat transport in the subsurface containing permafrost. The northern central Tibet Plateau was used as an example of model application. Modeling results show that in a yearly cycle, groundwater flow occurs in the active layer from May to October. Maximum groundwater discharge to the surface lags the maximum subsurface temperature by two months. Under an increasing air temperature scenario of 3?C per 100 years, over the initial 40-year period, the active layer thickness can increase by three-fold. Annual groundwater discharge to the surface can experience a similar three-fold increase in the same period. An implication of these modeling results is that with increased warming there will be more groundwater flow in the active layer and therefore increased groundwater discharge to rivers. However, this finding only holds if sufficient upgradient water is available to replenish the increased discharge. Otherwise, there will be an overall lowering of the water table in the recharge portion of the catchment.

Modular evaluation method for subsurface activities (MEMSA). A novel approach for integrating social acceptance in a permit decision-making process for subsurface activities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Os, Herman W.A. van, E-mail: h.w.a.van.os@rug.nl; Herber, Rien, E-mail: rien.herber@rug.nl; Scholtens, Bert, E-mail: l.j.r.scholtens@rug.nl

We investigate how the decision support system ‘Modular Evaluation Method Subsurface Activities’ (MEMSA) can help facilitate an informed decision-making process for permit applications of subsurface activities. To this end, we analyze the extent the MEMSA approach allows for a dialogue between stakeholders in a transparent manner. We use the exploration permit for the underground gas storage facility at the Pieterburen salt dome (Netherlands) as a case study. The results suggest that the MEMSA approach is flexible enough to adjust to changing conditions. Furthermore, MEMSA provides a novel way for identifying structural problems and possible solutions in permit decision-making processes formore » subsurface activities, on the basis of the sensitivity analysis of intermediate rankings. We suggest that the planned size of an activity should already be specified in the exploration phase, because this would allow for a more efficient use of the subsurface as a whole. We conclude that the host community should be involved to a greater extent and in an early phase of the permit decision-making process, for example, already during the initial analysis of the project area of a subsurface activity. We suggest that strategic national policy goals are to be re-evaluated on a regular basis, in the form of a strategic vision for the subsurface, to account for timing discrepancies between the realization of activities and policy deadlines, because this discrepancy can have a large impact on the necessity and therefore acceptance of a subsurface activity.« less

Using molecular-scale tracers to investigate transport of agricultural pollutants in soil and water

NASA Astrophysics Data System (ADS)

Lloyd, C.; Michaelides, K.; Chadwick, D.; Dungait, J.; Evershed, R. P.

2012-12-01

We explore the use of molecular-scale tracers to investigate the transport of potential pollutants due to the application of slurry to soil. The molecular-scale approach allows us to separate the pollutants which are moved to water bodies through sediment-bound and dissolved transport pathways. Slurry is applied to agricultural land to as a soil-improver across a wide-range of topographic and climatic regimes, hence a set of experiments were designed to assess the effect of changing slope gradient and rainfall intensity on the transport of pollutants. The experiments were carried out using University of Bristol's TRACE (Test Rig for Advancing Connectivity Experiments) facility. The facility includes a dual axis soil slope (6 x 2.5 x 0.3 m3) and 6-nozzle rainfall simulator, which enables the manipulation of the slope to simulate different slope gradient and rainfall scenarios. Cattle slurry was applied to the top 1 metre strip of the experimental soil slope followed by four rainfall simulations, where the gradient (5° & 10°) and the rainfall intensity (60 & 120 mm hr-1) were co-varied. Leachate was sampled from different flow pathways (surface, subsurface and percolated) via multiple outlets on the slope throughout the experiments and soil cores were taken from the slope after each experiment. Novel tracers were used to trace the pollutants in both dissolved and sediment-bound forms. Fluorescence spectroscopy was used to trace dissolved slurry-derived material via water flow pathways, as the slurry was found to have a distinct signature compared with the soil. The fluorescence signatures of the leachates were compared with those of many organic compounds in order to characterise the origin of the signal. This allowed the assessment of the longevity of the signal in the environment to establish if it could be used as a robust long-term tracer of slurry material in water or if would be subject to transform processes through time. 5-βstanols, organic compounds unique to ruminant faeces, were used to trace the transport of sediment-bound pollutants from the slurry which could be transported into water bodies via erosion processes. The results showed that contributions of potential pollutants from the surface and subsurface flow pathways and from the eroded sediment differ according to slope gradient and rainfall intensity. Therefore, as the contribution of each of these pathways changes in response to rainfall and slope gradient, the pollution risk also changes accordingly, as different organic compounds are mobilised at varying rates. Rapid hydrological response to rainfall results in erosion and surface transport of sediment-bound and dissolved pollutants, creating an immediate contamination threat. However, conditions resulting in a slower hydrological response and the predominance of flow percolation over surface runoff results in higher rates of dissolved pollutant transport through the soil layers which risks contamination of subsurface and deeper ground-water systems. These experiments provide insight into the pathways and timing of contaminant transport with potential implications for understanding contamination risk from the transfer of slurry from land to water bodies. Understanding this threat is critical at a time when pressure is on to develop land-management strategies to reduce pollution alongside maintaining food security.

Modelling of spatial contaminant probabilities of occurrence of chlorinated hydrocarbons in an urban aquifer.

PubMed

Greis, Tillman; Helmholz, Kathrin; Schöniger, Hans Matthias; Haarstrick, Andreas

2012-06-01

In this study, a 3D urban groundwater model is presented which serves for calculation of multispecies contaminant transport in the subsurface on the regional scale. The total model consists of two submodels, the groundwater flow and reactive transport model, and is validated against field data. The model equations are solved applying finite element method. A sensitivity analysis is carried out to perform parameter identification of flow, transport and reaction processes. Coming from the latter, stochastic variation of flow, transport, and reaction input parameters and Monte Carlo simulation are used in calculating probabilities of pollutant occurrence in the domain. These probabilities could be part of determining future spots of contamination and their measure of damages. Application and validation is exemplarily shown for a contaminated site in Braunschweig (Germany), where a vast plume of chlorinated ethenes pollutes the groundwater. With respect to field application, the methods used for modelling reveal feasible and helpful tools to assess natural attenuation (MNA) and the risk that might be reduced by remediation actions.

Quantifying the surface subsurface biogeochemical coupling during the VERTIGO ALOHA and K2 studies

NASA Astrophysics Data System (ADS)

Boyd, Philip W.; Gall, Mark P.; Silver, Mary W.; Coale, Susan L.; Bidigare, Robert R.; Bishop, James L. K. B.

2008-07-01

A central question addressed by the VERtical Transport In the Global Ocean (VERTIGO) study was 'What controls the efficiency of particle export between the surface and subsurface ocean'? Here, we present data from sites at ALOHA (N Central Pacific Gyre) and K2 (NW subarctic Pacific) on phytoplankton processes, and relate them via a simple planktonic foodweb model, to subsurface particle export (150-500 m). Three key factors enable quantification of the surface-subsurface coupling: a sampling design to overcome the temporal lag and spatial displacement between surface and subsurface processes; data on the size partitioning of net primary production (NPP) and subsequent transformations prior to export; estimates of the ratio of algal- to faecal-mediated vertical export flux. At ALOHA, phytoplankton were characterized by low stocks, NPP, Fv/ Fm (N-limited), and were dominated by picoplankton. The HNLC waters at K2 were characterized by both two-fold changes in NPP and floristic shifts (high to low proportion of diatoms) between deployment 1 and 2. Prediction of export exiting the euphotic zone was based on size partitioning of NPP, a copepod-dominated foodweb and a ratio of 0.2 (ALOHA) and 0.1 (K2) for algal:faecal particle flux. Predicted export was 20-22 mg POC m -2 d -1 at ALOHA (i.e. 10-11% NPP (0-125 m); 1.1-1.2×export flux at 150 m ( E150). At K2, export was 111 mg C m -2 d -1 (21% NPP (0-50 m); 1.8× E150) and 33 mg POC m -2 d -1 (11% NPP, 0-55 m); 1.4× E150) for deployments 1 and 2, respectively. This decrease in predicted export at K2 matches the observed trend for E150. Also, the low attenuation of export flux from 60 to 150 m is consistent with that between 150 and 500 m. This strong surface-subsurface coupling suggests that phytoplankton productivity and floristics play a key role at K2 in setting export flux, and moreover that pelagic particle transformations by grazers strongly influence to what extent sinking particles are further broken down in the underlying waters of the Twilight Zone.

Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study

USGS Publications Warehouse

Molins, S.; Mayer, K.U.

2007-01-01

The two‐way coupling that exists between biogeochemical reactions and vadose zone transport processes, in particular gas phase transport, determines the composition of soil gas. To explore these feedback processes quantitatively, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described on the basis of the dusty gas model, which accounts for all relevant gas diffusion mechanisms. The simulation of gas attenuation in partially saturated landfill soil covers, methane production, and oxidation in aquifers contaminated by organic compounds (e.g., an oil spill site) and pyrite oxidation in mine tailings demonstrate that both diffusive and advective gas transport can be affected by geochemical reactions. Methane oxidation in landfill covers reduces the existing upward pressure gradient, thereby decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, methane oxidation causes a reversal in the direction of gas advection, which results in advective transport toward the zone of oxidation both from the ground surface and the deeper zone of methane production. Both diffusion and advection contribute to supply atmospheric oxygen into the subsurface, and methane emissions to the atmosphere are averted. During pyrite oxidation in mine tailings, pressure reduction in the reaction zone drives advective gas flow into the sediment column, enhancing the oxidation process. In carbonate‐rich mine tailings, calcite dissolution releases carbon dioxide, which partly offsets the pressure reduction caused by O2 consumption.

Subsurface iron and arsenic removal for shallow tube well drinking water supply in rural Bangladesh.

PubMed

van Halem, D; Olivero, S; de Vet, W W J M; Verberk, J Q J C; Amy, G L; van Dijk, J C

2010-11-01

Subsurface iron and arsenic removal has the potential to be a cost-effective technology to provide safe drinking water in rural decentralized applications, using existing shallow tube wells. A community-scale test facility in Bangladesh was constructed for injection of aerated water (∼1 m(3)) into an anoxic aquifer with elevated iron (0.27 mmolL(-1)) and arsenic (0.27μmolL(-1)) concentrations. The injection (oxidation) and abstraction (adsorption) cycles were monitored at the test facility and simultaneously simulated in the laboratory with anoxic column experiments. Dimensionless retardation factors (R) were determined to represent the delayed arrival of iron or arsenic in the well compared to the original groundwater. At the test facility the iron removal efficacies increased after every injection-abstraction cycle, with retardation factors (R(Fe)) up to 17. These high removal efficacies could not be explained by the theory of adsorptive-catalytic oxidation, and therefore other ((a)biotic or transport) processes have contributed to the system's efficacy. This finding was confirmed in the anoxic column experiments, since the mechanism of adsorptive-catalytic oxidation dominated in the columns and iron removal efficacies did not increase with every cycle (stable at R(Fe)=∼8). R(As) did not increase after multiple cycles, it remained stable around 2, illustrating that the process which is responsible for the effective iron removal did not promote the co-removal of arsenic. The columns showed that subsurface arsenic removal was an adsorptive process and only the freshly oxidized adsorbed iron was available for the co-adsorption of arsenic. This indicates that arsenic adsorption during subsurface treatment is controlled by the amount of adsorbed iron that is oxidized, and not by the amount of removed iron. For operational purposes this is an important finding, since apparently the oxygen concentration of the injection water does not control the subsurface arsenic removal, but rather the injection volume. Additionally, no relation has been observed in this study between the amount of removed arsenic at different molar Fe:As ratios (28, 63, and 103) of the groundwater. It is proposed that the removal of arsenic was limited by the presence of other anions, such as phosphate, competing for the same adsorption sites. Copyright © 2010 Elsevier Ltd. All rights reserved.

INTERNET COURSE ON MODELING SUBSURFACE TRANSPORT OF PETROLEUM HYDROCARBONS

EPA Science Inventory

Assessment of leaks from underground storage tanks relies on knowledge of contaminant fate and transport, hydrology and in some cases modeling. EPA is developing an interactive, on-line training course to provide states with a low-cost training opportunity for these areas. Two ...

CONTAMINANT TRANSPORT RESULTING FROM MULTICOMPONENT NONAQUEOUS PHASE LIQUID POOL DISSOLUTION IN THREE-DIMENSIONAL SUBSURFACE FORMATIONS (R823579)

EPA Science Inventory

A semi-analytical method for simulating transient contaminant transport originating from the dissolution of multicomponent nonaqueous phase liquid (NAPL) pools in three-dimensional, saturated, homogeneous porous media is presented. Each dissolved component may undergo first-order...

Subsurface Hydrology: Data Integration for Properties and Processes

NASA Astrophysics Data System (ADS)

Hyndman, David W.; Day-Lewis, Frederick D.; Singha, Kamini

Groundwater is a critical resource and the PrinciPal source of drinking water for over 1.5 billion people. In 2001, the National Research Council cited as a "grand challenge" our need to understand the processes that control water movement in the subsurface. This volume faces that challenge in terms of data integration between complex, multi-scale hydrologie processes, and their links to other physical, chemical, and biological processes at multiple scales. Subsurface Hydrology: Data Integration for Properties and Processes presents the current state of the science in four aspects: • Approaches to hydrologie data integration • Data integration for characterization of hydrologie properties • Data integration for understanding hydrologie processes • Meta-analysis of current interpretations Scientists and researchers in the field, the laboratory, and the classroom will find this work an important resource in advancing our understanding of subsurface water movement.

Parametric sensitivity analysis of leachate transport simulations at landfills.

PubMed

Bou-Zeid, E; El-Fadel, M

2004-01-01

This paper presents a case study in simulating leachate generation and transport at a 2000 ton/day landfill facility and assesses leachate migration away from the landfill in order to control associated environmental impacts, particularly on groundwater wells down gradient of the site. The site offers unique characteristics in that it is a former quarry converted to a landfill and is planned to have refuse depths that could reach 100 m, making it one of the deepest in the world. Leachate quantity and potential percolation into the subsurface are estimated using the Hydrologic Evaluation of Landfill Performance (HELP) model. A three-dimensional subsurface model (PORFLOW) was adopted to simulate ground water flow and contaminant transport away from the site. A comprehensive sensitivity analysis to leachate transport control parameters was also conducted. Sensitivity analysis suggests that changes in partition coefficient, source strength, aquifer hydraulic conductivity, and dispersivity have the most significant impact on model output indicating that these parameters should be carefully selected when similar modeling studies are performed. Copyright 2004 Elsevier Ltd.

Quantification of the effect of temperature gradients in soils on subsurface radon signal

NASA Astrophysics Data System (ADS)

Haquin, Gustavo; Ilzycer, Danielle; Kamai, Tamir; Zafrir, Hovav; Weisbrod, Noam

2017-04-01

Temperature gradients that develop in soils due to atmospheric temperature cycles are factors of primary importance in determining the rates and directions of subsurface gas flow. Models including mechanisms of thermal convection and thermal diffusion partially explain the impact of temperature gradients on subsurface radon transport. However, the overall impact of temperature gradients on subsurface radon transport is still not well understood. A laboratory setup was designed and built to experimentally investigate the influence of temperature gradients on radon transport under well controlled conditions. A 60 cm diameter and 120 cm tall column was thermally insulated except from the atmosphere-soil interface, such that it was constructed to simulate field conditions where temperature gradients in soils are developed following atmospheric temperature cycles. The column was filled with fine grinded phosphate rock which provided the porous media with radon source. Radon in soil-air was continuously monitored using NaI gamma detectors positioned at different heights along the column. Soil temperature, differential pressure, and relative humidity were monitored along the column. Experiments based on steep and gradual stepwise changes in ambient temperature were conducted. Absolute changes on radon levels in the order of 10-30% were measured at temperature gradients of up to ±20oC/m. Results showed a non-linear correlation between the temperature gradient and the subsurface radon concentration. An asymmetric relationship between the radon concentration and the temperature gradients for ΔT>0 and ΔT<0 was also observed. Laboratory simulations of the time- and depth-dependent temperature wave functions with frequencies ranged from a daily cycle to few days were performed. In response to the harmonic temperature behaviour radon oscillations at similar frequencies were detected correspondingly. In this work a quantitative relationship between radon and temperature gradients will be presented for cases beyond the classical conditions for thermal convection and thermal diffusion.

STATE WATER RESOURCES RESEARCH INSTITUTE PROGRAM: GROUND WATER RESEARCH.

USGS Publications Warehouse

Burton, James S.; ,

1985-01-01

This paper updates a review of the accomplishments of the State Water Resources Research Program in ground water contamination research. The aim is to assess the progress made towards understanding the mechanisms of ground water contamination and based on this understanding, to suggest procedures for the prevention and control of ground water contamination. The following research areas are covered: (1) mechanisms of organic contaminant transport in the subsurface environment; (2) bacterial and viral contamination of ground water from landfills and septic tank systems; (3) fate and persistence of pesticides in the subsurface; (4) leachability and transport of ground water pollutants from coal production and utilization; and (5) pollution of ground water from mineral mining activities.

Effect of small scale transport processes on phytoplankton distribution in coastal seas.

PubMed

Hernández-Carrasco, Ismael; Orfila, Alejandro; Rossi, Vincent; Garçon, Veronique

2018-06-05

Coastal ocean ecosystems are major contributors to the global biogeochemical cycles and biological productivity. Physical factors induced by the turbulent flow play a crucial role in regulating marine ecosystems. However, while large-scale open-ocean dynamics is well described by geostrophy, the role of multiscale transport processes in coastal regions is still poorly understood due to the lack of continuous high-resolution observations. Here, the influence of small-scale dynamics (O(3.5-25) km, i.e. spanning upper submesoscale and mesoscale processes) on surface phytoplankton derived from satellite chlorophyll-a (Chl-a) is studied using Lagrangian metrics computed from High-Frequency Radar currents. The combination of complementary Lagrangian diagnostics, including the Lagrangian divergence along fluid trajectories, provides an improved description of the 3D flow geometry which facilitates the interpretation of two non-exclusive physical mechanisms affecting phytoplankton dynamics and patchiness. Attracting small-scale fronts, unveiled by backwards Lagrangian Coherent Structures, are associated to negative divergence where particles and Chl-a standing stocks cluster. Filaments of positive divergence, representing large accumulated upward vertical velocities and suggesting accrued injection of subsurface nutrients, match areas with large Chl-a concentrations. Our findings demonstrate that an accurate characterization of small-scale transport processes is necessary to comprehend bio-physical interactions in coastal seas.

Facilitated strontium transport by remobilization of strontium-containing secondary precipitates in Hanford Site subsurface.

PubMed

Wang, Guohui; Um, Wooyong

2013-03-15

Significantly enhanced immobilization of radionuclides (such as (90)Sr and (137)Cs) due to adsorption and coprecipitation with neo-formed colloid-sized secondary precipitates has been reported at the U.S. Department of Energy's Hanford Site. However, the stability of these secondary precipitates containing radionuclides in the subsurface under changeable field conditions is not clear. Here, the authors tested the remobilization possibility of Sr-containing secondary precipitates (nitrate-cancrinite) in the subsurface using saturated column experiments under different geochemical and flow conditions. The columns were packed with quartz sand that contained secondary precipitates (nitrate-cancrinite containing Sr), and leached using colloid-free solutions under different flow rates, varying pH, and ionic strength conditions. The results indicate remobilization of the neo-formed secondary precipitates could be possible given a change of pH of ionic strength and flow rate conditions. The remobility of the neo-formed precipitates increased with the rise in the leaching solution flow rate and pH (in a range of pH 4-11), as well as with decreasing solution ionic strength. The increased mobility of Sr-containing secondary precipitates with changing background conditions can be a potential source for additional radionuclide transport in Hanford Site subsurface environments. Published by Elsevier B.V.

Manipulation of subsurface carbon nanoparticles in Bi 2 Sr 2 CaCu 2 O 8 + δ using a scanning tunneling microscope

DOE PAGES

Stollenwerk, A. J.; Hurley, N.; Beck, B.; ...

2015-03-19

In this study, we present evidence that subsurface carbon nanoparticles in Bi₂Sr₂CaCu₂O 8+δ can be manipulated with nanometer precision using a scanning tunneling microscope. High resolution images indicate that most of the carbon particles remain subsurface after transport observable as a local increase in height as the particle pushes up on the surface. Tunneling spectra in the vicinity of these protrusions exhibit semiconducting characteristics with a band gap of approximately 1.8 eV, indicating that the incorporation of carbon locally alters the electronic properties near the surface.

A reaction-based paradigm to model reactive chemical transport in groundwater with general kinetic and equilibrium reactions.

PubMed

Zhang, Fan; Yeh, Gour-Tsyh; Parker, Jack C; Brooks, Scott C; Pace, Molly N; Kim, Young-Jin; Jardine, Philip M; Watson, David B

2007-06-16

This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss-Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing N(E) equilibrium reactions and a set of reactive transport equations of M-N(E) kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions.

Geologic and climatic controls on streamflow generation processes in a complex eogenetic karst basin

NASA Astrophysics Data System (ADS)

Vibhava, F.; Graham, W. D.; Maxwell, R. M.

2012-12-01

Streamflow at any given location and time is representative of surface and subsurface contributions from various sources. The ability to fully identify the factors controlling these contributions is key to successfully understanding the transport of contaminants through the system. In this study we developed a fully integrated 3D surface water-groundwater-land surface model, PARFLOW, to evaluate geologic and climatic controls on streamflow generation processes in a complex eogenetic karst basin in North Central Florida. In addition to traditional model evaluation criterion, such as comparing field observations to model simulated streamflow and groundwater elevations, we quantitatively evaluated the model's predictions of surface-groundwater interactions over space and time using a suite of binary end-member mixing models that were developed using observed specific conductivity differences among surface and groundwater sources throughout the domain. Analysis of model predictions showed that geologic heterogeneity exerts a strong control on both streamflow generation processes and land atmospheric fluxes in this watershed. In the upper basin, where the karst aquifer is overlain by a thick confining layer, approximately 92% of streamflow is "young" event flow, produced by near stream rainfall. Throughout the upper basin the confining layer produces a persistent high surficial water table which results in high evapotranspiration, low groundwater recharge and thus negligible "inter-event" streamflow. In the lower basin, where the karst aquifer is unconfined, deeper water tables result in less evapotranspiration. Thus, over 80% of the streamflow is "old" subsurface flow produced by diffuse infiltration through the epikarst throughout the lower basin, and all surface contributions to streamflow originate in the upper confined basin. Climatic variability provides a secondary control on surface-subsurface and land-atmosphere fluxes, producing significant seasonal and interannual variability in these processes. Spatial and temporal patterns of evapotranspiration, groundwater recharge and streamflow generation processes reveal potential hot spots and hot moments for surface and groundwater contamination in this basin.

FATE AND TRANSPORT MODELING OF CONTAMINANTS OF CONCERN FROM A CAFO IN AN AGRICULTURAL WATERSHED

EPA Science Inventory

The groundwater flow and transport modeling effort will require hydrogeological site characterization and the development of a conceptual flow model for the site. Site characterization will involve an assessment of both the surface and subsurface and be accomplished through joint...

A shallow subsurface controlled release facility in Bozeman, Montana, USA, for testing near surface CO2 detection techniques and transport models

USGS Publications Warehouse

Spangler, L.H.; Dobeck, L.M.; Repasky, K.S.; Nehrir, A.R.; Humphries, S.D.; Keith, C.J.; Shaw, J.A.; Rouse, J.H.; Cunningham, A.B.; Benson, S.M.; Oldenburg, C.M.; Lewicki, J.L.; Wells, A.W.; Diehl, J.R.; Strazisar, B.R.; Fessenden, J.E.; Rahn, T.A.; Amonette, J.E.; Barr, J.L.; Pickles, W.L.; Jacobson, J.D.; Silver, E.A.; Male, E.J.; Rauch, H.W.; Gullickson, K.S.; Trautz, R.; Kharaka, Y.; Birkholzer, J.; Wielopolski, L.

2010-01-01

A controlled field pilot has been developed in Bozeman, Montana, USA, to study near surface CO2 transport and detection technologies. A slotted horizontal well divided into six zones was installed in the shallow subsurface. The scale and CO2 release rates were chosen to be relevant to developing monitoring strategies for geological carbon storage. The field site was characterized before injection, and CO2 transport and concentrations in saturated soil and the vadose zone were modeled. Controlled releases of CO2 from the horizontal well were performed in the summers of 2007 and 2008, and collaborators from six national labs, three universities, and the U.S. Geological Survey investigated movement of CO2 through the soil, water, plants, and air with a wide range of near surface detection techniques. An overview of these results will be presented. ?? 2009 The Author(s).

Geo-material surface modification of microchips using layer-by-layer (LbL) assembly for subsurface energy and environmental applications.

PubMed

Zhang, Y Q; Sanati-Nezhad, A; Hejazi, S H

2018-01-16

A key constraint in the application of microfluidic technology to subsurface flow and transport processes is the surface discrepancy between microchips and the actual rocks/soils. This research employs a novel layer-by-layer (LbL) assembly technology to produce rock-forming mineral coatings on microchip surfaces. The outcome of the work is a series of 'surface-mimetic micro-reservoirs (SMMR)' that represent multi-scales and multi-types of natural rocks/soils. For demonstration, the clay pores of sandstones and mudrocks are reconstructed by representatively coating montmorillonite and kaolinite in polydimethylsiloxane (PDMS) microchips in a wide range of channel sizes (width of 10-250 μm, depth of 40-100 μm) and on glass substrates. The morphological and structural properties of mineral coatings are characterized using a scanning electron microscope (SEM), optical microscope and profilometer. The coating stability is tested by dynamic flooding experiments. The surface wettability is characterized by measuring mineral oil-water contact angles. The results demonstrate the formation of nano- to micro-scale, fully-covered and stable mineral surfaces with varying wetting properties. There is an opportunity to use this work in the development of microfluidic technology-based applications for subsurface energy and environmental research.

Groundwater flow with energy transport and water-ice phase change: Numerical simulations, benchmarks, and application to freezing in peat bogs

USGS Publications Warehouse

McKenzie, J.M.; Voss, C.I.; Siegel, D.I.

2007-01-01

In northern peatlands, subsurface ice formation is an important process that can control heat transport, groundwater flow, and biological activity. Temperature was measured over one and a half years in a vertical profile in the Red Lake Bog, Minnesota. To successfully simulate the transport of heat within the peat profile, the U.S. Geological Survey's SUTRA computer code was modified. The modified code simulates fully saturated, coupled porewater-energy transport, with freezing and melting porewater, and includes proportional heat capacity and thermal conductivity of water and ice, decreasing matrix permeability due to ice formation, and latent heat. The model is verified by correctly simulating the Lunardini analytical solution for ice formation in a porous medium with a mixed ice-water zone. The modified SUTRA model correctly simulates the temperature and ice distributions in the peat bog. Two possible benchmark problems for groundwater and energy transport with ice formation and melting are proposed that may be used by other researchers for code comparison. ?? 2006 Elsevier Ltd. All rights reserved.

Higher and lowest order mixed finite element approximation of subsurface flow problems with solutions of low regularity

NASA Astrophysics Data System (ADS)

Bause, Markus

2008-02-01

In this work we study mixed finite element approximations of Richards' equation for simulating variably saturated subsurface flow and simultaneous reactive solute transport. Whereas higher order schemes have proved their ability to approximate reliably reactive solute transport (cf., e.g. [Bause M, Knabner P. Numerical simulation of contaminant biodegradation by higher order methods and adaptive time stepping. Comput Visual Sci 7;2004:61-78]), the Raviart- Thomas mixed finite element method ( RT0) with a first order accurate flux approximation is popular for computing the underlying water flow field (cf. [Bause M, Knabner P. Computation of variably saturated subsurface flow by adaptive mixed hybrid finite element methods. Adv Water Resour 27;2004:565-581, Farthing MW, Kees CE, Miller CT. Mixed finite element methods and higher order temporal approximations for variably saturated groundwater flow. Adv Water Resour 26;2003:373-394, Starke G. Least-squares mixed finite element solution of variably saturated subsurface flow problems. SIAM J Sci Comput 21;2000:1869-1885, Younes A, Mosé R, Ackerer P, Chavent G. A new formulation of the mixed finite element method for solving elliptic and parabolic PDE with triangular elements. J Comp Phys 149;1999:148-167, Woodward CS, Dawson CN. Analysis of expanded mixed finite element methods for a nonlinear parabolic equation modeling flow into variably saturated porous media. SIAM J Numer Anal 37;2000:701-724]). This combination might be non-optimal. Higher order techniques could increase the accuracy of the flow field calculation and thereby improve the prediction of the solute transport. Here, we analyse the application of the Brezzi- Douglas- Marini element ( BDM1) with a second order accurate flux approximation to elliptic, parabolic and degenerate problems whose solutions lack the regularity that is assumed in optimal order error analyses. For the flow field calculation a superiority of the BDM1 approach to the RT0 one is observed, which however is less significant for the accompanying solute transport.

The influence of humic acid and clay content on the transport of polymer-coated iron nanoparticles through sand.

PubMed

Jung, Bahngmi; O'Carroll, Denis; Sleep, Brent

2014-10-15

The introduction of nanoscale zero valent iron (nZVI) into the subsurface has recently received significant attention as a potentially effective method for remediation of source zones of chlorinated solvents present as dense nonaqueous phase liquids (DNAPL). One of the challenges in the deployment of nZVI is to achieve good subsurface nZVI mobility to permit delivery of the nZVI to the target treatment zone. Stabilization of nZVI with various polymers has shown promise for enhancing nZVI subsurface mobility, but the impact of subsurface conditions on nZVI mobility has not been fully explored. In this study, the effect of humic acid and kaolinite on the transport of polymer-stabilized nZVI (carboxylmethyl cellulose-surface modified nZVI, CMC90K-RNIP) in sand was investigated using column experiments. In addition, effects of electrolytes on the stability of CMC90K-RNIP in the presence of humic acid, and the stability of humic acid-coated reactive nanoscale iron particles (HA-RNIP) at various humic acid concentrations were investigated. Humic acid enhanced the mobility of bare RNIP, whereas the transport of CMC90K-RNIP was not significantly affected by humic acid injected as a background solution, except at the highest concentration of 500mg/L. At lower pore water velocity, the effect of humic acid on the transport of CMC90K-RNIP was greater than that at high water velocity. Adding kaolinite up to 2% by weight to the sand column reduced the retention of CMC90K-RNIP, but further increases in kaolinite content (to 5%) did not significantly affect nZVI retention. The impact of kaolinite on nZVI retention was more pronounced at lower pore water velocities. Copyright © 2014 Elsevier B.V. All rights reserved.

Deep subsurface microbial processes

USGS Publications Warehouse

Lovley, D.R.; Chapelle, F.H.

1995-01-01

Information on the microbiology of the deep subsurface is necessary in order to understand the factors controlling the rate and extent of the microbially catalyzed redox reactions that influence the geophysical properties of these environments. Furthermore, there is an increasing threat that deep aquifers, an important drinking water resource, may be contaminated by man's activities, and there is a need to predict the extent to which microbial activity may remediate such contamination. Metabolically active microorganisms can be recovered from a diversity of deep subsurface environments. The available evidence suggests that these microorganisms are responsible for catalyzing the oxidation of organic matter coupled to a variety of electron acceptors just as microorganisms do in surface sediments, but at much slower rates. The technical difficulties in aseptically sampling deep subsurface sediments and the fact that microbial processes in laboratory incubations of deep subsurface material often do not mimic in situ processes frequently necessitate that microbial activity in the deep subsurface be inferred through nonmicrobiological analyses of ground water. These approaches include measurements of dissolved H2, which can predict the predominant microbially catalyzed redox reactions in aquifers, as well as geochemical and groundwater flow modeling, which can be used to estimate the rates of microbial processes. Microorganisms recovered from the deep subsurface have the potential to affect the fate of toxic organics and inorganic contaminants in groundwater. Microbial activity also greatly influences 1 the chemistry of many pristine groundwaters and contributes to such phenomena as porosity development in carbonate aquifers, accumulation of undesirably high concentrations of dissolved iron, and production of methane and hydrogen sulfide. Although the last decade has seen a dramatic increase in interest in deep subsurface microbiology, in comparison with the study of other habitats, the study of deep subsurface microbiology is still in its infancy.

Radar Imaging of Europa's Subsurface Properties and Processes: The View from Earth

NASA Astrophysics Data System (ADS)

Blankenship, D. D.; Moore, W. B.; Young, D. A.; Peters, M. E.

2007-12-01

A primary objective of future Europa studies will be to characterize the distribution of shallow subsurface water as well as to identify any ice-ocean interface. Another objective will be to understand the formation of surface and subsurface features associated with interchange processes between any ocean and the surface. Achieving these objectives will require either direct or inferred knowledge of the position of any ice/water interfaces as well as any brine or layer pockets. We will review the hypothesized processes that control the thermal, compositional and structural (TCS) properties, and therefore the dielectric character, of the subsurface of Europa's icy shell. Our approach will be to extract the TCS properties for various subsurface processes thought to control the formation of major surface (e.g., ridges/bands, lenticulae, chaos, cratering...) and subsurface (e.g., rigid shell eutectics, diapirs, accretionary lenses ...) features on Europa. We will then assess the spectrum of analog processes and TCS properties represented by Earth's cryosphere including both Arctic and Antarctic ice sheets, ice shelves and valley glaciers. There are few complete analogs over the full TCS space but, because of the wide range of ice thickness, impurities and strain rates for Earth's cryosphere, there are many more analogs than many Earth and planetary researchers might imagine for significant portions of this space (e.g., bottom crevasses, marine ice shelf/subglacial lake accretion, surging polythermal glaciers...).Our ultimate objective is to use these Earth analog studies to define the radar imaging approach for Europa's subsurface that will be most useful for supporting/refuting the hypotheses for the formation of major surface/subsurface features as well as for "pure" exploration of Europa's icy shell and its interface with the underlying ocean.

Examining Changes in Radioxenon Isotope Activity Ratios during Subsurface Transport

NASA Astrophysics Data System (ADS)

Annewandter, R.

2013-12-01

The Non-Proliferation Experiment (NPE) has demonstrated and modelled the usefulness of barometric pumping induced soil gas sampling during On-Site inspections. Gas transport has been widely studied with different numerical codes. However, gas transport of all radioxenons in the post-detonation regime and their possible fractionation is still neglected in the open literature. Atmospheric concentrations of the radioxenons Xe-135, Xe-133m, Xe-133 and Xe-131m can be used to discriminate between civilian releases (nuclear power plants or medical isotope facilities), and nuclear explosion sources. It is based on the isotopic activity ratio method. Yet it is not clear whether subsurface migration of the radioxenons, with eventual release into the atmosphere, can affect the activity ratios due to fractionation. Fractionation can be caused by different diffusivities due to mass differences between the radioxenons. A previous study showed surface arrival time of a chemically inert gaseous tracer is affected by its diffusivity. They observed detectable amount for SF6 50 days after detonation and 375 days for He-3. They predict 50 and 80 days for Xe-133 and Ar-37 respectively. Cyclical changes in atmospheric pressure can drive subsurface gas transport. This barometric pumping phenomenon causes an oscillatoric flow in upward trending fractures which, combined with diffusion into the porous matrix, leads to a net transport of gaseous components - a ratcheting effect. We use a general purpose reservoir simulator (Complex System Modelling Platform, CSMP++) which has been applied in a range of fields such as deep geothermal systems, three-phase black oil simulations , fracture propagation in fractured, porous media, Navier-Stokes pore-scale modelling among others. It is specifically designed to account for structurally complex geologic situation of fractured, porous media. Parabolic differential equations are solved by a continuous Galerkin finite-element method, hyperbolic differential equations by a complementary finite volume method. The parabolic and hyperbolic problem can be solved separately using the operator-splitting method (Implicit Pressure Explicit Saturation, IMPES). The resulting system of linear equations is solved by the algebraic multigrid library SAMG, developed at the Fraunhofer Institute for Algorithms and Scientific Computing. CSMP++ is developed at Montan University of Leoben, ETH Zuerich, Imperial College London and Heriot-Watt University in Edinburgh. To date, there has been no research investigating how subsurface transport impacts isotope activity ratios. The isotopic activity ratio method can be used to discriminate between civil release or nuclear explosion sources. This study examines possible fractionation of Xe-135, Xe-133m, Xe-133, Xe-131m during barometric pumping-driven subsurface migration, which can affect surface arrival times and isotopic activity ratios. Surface arrival times for the Noble gases Kr-81, Kr-85 and Ar-39 are also calculated.

Modelling rapid subsurface flow at the hillslope scale with explicit representation of preferential flow paths

NASA Astrophysics Data System (ADS)

Wienhöfer, J.; Zehe, E.

2012-04-01

Rapid lateral flow processes via preferential flow paths are widely accepted to play a key role for rainfall-runoff response in temperate humid headwater catchments. A quantitative description of these processes, however, is still a major challenge in hydrological research, not least because detailed information about the architecture of subsurface flow paths are often impossible to obtain at a natural site without disturbing the system. Our study combines physically based modelling and field observations with the objective to better understand how flow network configurations influence the hydrological response of hillslopes. The system under investigation is a forested hillslope with a small perennial spring at the study area Heumöser, a headwater catchment of the Dornbirnerach in Vorarlberg, Austria. In-situ points measurements of field-saturated hydraulic conductivity and dye staining experiments at the plot scale revealed that shrinkage cracks and biogenic macropores function as preferential flow paths in the fine-textured soils of the study area, and these preferential flow structures were active in fast subsurface transport of artificial tracers at the hillslope scale. For modelling of water and solute transport, we followed the approach of implementing preferential flow paths as spatially explicit structures of high hydraulic conductivity and low retention within the 2D process-based model CATFLOW. Many potential configurations of the flow path network were generated as realisations of a stochastic process informed by macropore characteristics derived from the plot scale observations. Together with different realisations of soil hydraulic parameters, this approach results in a Monte Carlo study. The model setups were used for short-term simulation of a sprinkling and tracer experiment, and the results were evaluated against measured discharges and tracer breakthrough curves. Although both criteria were taken for model evaluation, still several model setups produced acceptable matches to the observed behaviour. These setups were selected for long-term simulation, the results of which were compared against water level measurements at two piezometers along the hillslope and the integral discharge response of the spring to reject some non-behavioural model setups and further reduce equifinality. The results of this study indicate that process-based modelling can provide a means to distinguish preferential flow networks on the hillslope scale when complementary measurements to constrain the range of behavioural model setups are available. These models can further be employed as a virtual reality to investigate the characteristics of flow path architectures and explore effective parameterisations for larger scale applications.

Earth Sciences Division annual report 1990

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

1991-06-01

This Annual Report presents summaries of selected representative research activities grouped according to the principal disciplines of the Earth Sciences Division: Reservoir Engineering and Hydrogeology, Geology and Geochemistry, and Geophysics and Geomechanics. Much of the Division`s research deals with the physical and chemical properties and processes in the earth`s crust, from the partially saturated, low-temperature near-surface environment to the high-temperature environments characteristic of regions where magmatic-hydrothermal processes are active. Strengths in laboratory and field instrumentation, numerical modeling, and in situ measurement allow study of the transport of mass and heat through geologic media -- studies that now include the appropriatemore » chemical reactions and the hydraulic-mechanical complexities of fractured rock systems. Of particular note are three major Division efforts addressing problems in the discovery and recovery of petroleum, the application of isotope geochemistry to the study of geodynamic processes and earth history, and the development of borehole methods for high-resolution imaging of the subsurface using seismic and electromagnetic waves. In 1989 a major DOE-wide effort was launched in the areas of Environmental Restoration and Waste Management. Many of the methods previously developed for and applied to deeper regions of the earth will in the coming years be turned toward process definition and characterization of the very shallow subsurface, where man-induced contaminants now intrude and where remedial action is required.« less

MICROSCALE METABOLIC, REDOX AND ABIOTIC REACTIONS IN HANFORD 300 AREA SUBSURFACE SEDIMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beyenal, Haluk; McLEan, Jeff; Majors, Paul

2013-11-14

The Hanford 300 Area is a unique site due to periodic hydrologic influence of river water resulting in changes in groundwater elevation and flow direction. This area is also highly subject to uranium remobilization, the source of which is currently believed to be the region at the base of the vadose zone that is subject to period saturation due to the changes in the water levels in the Columbia River. We found that microbial processes and redox and abiotic reactions which operate at the microscale were critical to understanding factors controlling the macroscopic fate and transport of contaminants in themore » subsurface. The combined laboratory and field research showed how microscale conditions control uranium mobility and how biotic, abiotic and redox reactions relate to each other. Our findings extended the current knowledge to examine U(VI) reduction and immobilization using natural 300 Area communities as well as selected model organisms on redox-sensitive and redox-insensitive minerals. Using innovative techniques developed specifically to probe biogeochemical processes at the microscale, our research expanded our current understanding of the roles played by mineral surfaces, bacterial competition, and local biotic, abiotic and redox reaction rates on the reduction and immobilization of uranium.« less

Further influence of the eastern boundary on the seasonal variability of the Atlantic Meridional Overturning Circulation at 26N

NASA Astrophysics Data System (ADS)

Baehr, Johanna; Schmidt, Christian

2016-04-01

The seasonal cycle of the Atlantic Meridional Overturning Circulation (AMOC) at 26.5 N has been shown to arise predominantly from sub-surface density variations at the Eastern boundary. Here, we suggest that these sub-surface density variations have their origin in the seasonal variability of the Canary Current system, in particular the Poleward Undercurrent (PUC). We use a high-resolution ocean model (STORM) for which we show that the seasonal variability resembles observations for both sub-surface density variability and meridional transports. In particular, the STORM model simulation density variations at the eastern boundary show seasonal variations reaching down to well over 1000m, a pattern that most model simulations systematically underestimate. We find that positive wind stress curl anomalies in late summer and already within one degree off the eastern boundary result -through water column stretching- in strong transport anomlies in PUC in fall, coherent down to 1000m depth. Simultaneously with a westward propagation of these transport anomalies, we find in winter a weak PUC between 200 m and 500m, and southward transports between 600m and 1300m. This variability is in agreement with the observationally-based suggestion of a seasonal reversal of the meridional transports at intermediate depths. Our findings extend earlier studies which suggested that the seasonal variability at of the meridional transports across 26N is created by changes in the basin-wide thermocline through wind-driven upwelling at the eastern boundary analyzing wind stress curl anomalies 2 degrees off the eastern boundary. Our results suggest that the investigation of AMOC variability and particular its seasonal cycle modulations require the analysis of boundary wind stress curl and the upper ocean transports within 1 degree off the eastern boundary. These findings also implicate that without high-resolution coverage of the eastern boundary, coarser model simulation might not fully represent the AMOC's seasonal variability.

Fluid-faulting interactions: Fracture-mesh and fault-valve behavior in the February 2014 Mammoth Mountain, California, earthquake swarm

USGS Publications Warehouse

Shelly, David R.; Taira, Taka’aki; Prejean, Stephanie; Hill, David P.; Dreger, Douglas S.

2015-01-01

Faulting and fluid transport in the subsurface are highly coupled processes, which may manifest seismically as earthquake swarms. A swarm in February 2014 beneath densely monitored Mammoth Mountain, California, provides an opportunity to witness these interactions in high resolution. Toward this goal, we employ massive waveform-correlation-based event detection and relative relocation, which quadruples the swarm catalog to more than 6000 earthquakes and produces high-precision locations even for very small events. The swarm's main seismic zone forms a distributed fracture mesh, with individual faults activated in short earthquake bursts. The largest event of the sequence, M 3.1, apparently acted as a fault valve and was followed by a distinct wave of earthquakes propagating ~1 km westward from the updip edge of rupture, 1–2 h later. Late in the swarm, multiple small, shallower subsidiary faults activated with pronounced hypocenter migration, suggesting that a broader fluid pressure pulse propagated through the subsurface.

Optical and electronic properties of sub-surface conducting layers in diamond created by MeV B-implantation at elevated temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Willems van Beveren, L. H., E-mail: laurensw@unimelb.edu.au; Bowers, H.; Ganesan, K.

2016-06-14

Boron implantation with in-situ dynamic annealing is used to produce highly conductive sub-surface layers in type IIa (100) diamond plates for the search of a superconducting phase transition. Here, we demonstrate that high-fluence MeV ion-implantation, at elevated temperatures avoids graphitization and can be used to achieve doping densities of 6 at. %. In order to quantify the diamond crystal damage associated with implantation Raman spectroscopy was performed, demonstrating high temperature annealing recovers the lattice. Additionally, low-temperature electronic transport measurements show evidence of charge carrier densities close to the metal-insulator-transition. After electronic characterization, secondary ion mass spectrometry was performed to mapmore » out the ion profile of the implanted plates. The analysis shows close agreement with the simulated ion-profile assuming scaling factors that take into account an average change in diamond density due to device fabrication. Finally, the data show that boron diffusion is negligible during the high temperature annealing process.« less

Influence of Si wafer thinning processes on (sub)surface defects

NASA Astrophysics Data System (ADS)

Inoue, Fumihiro; Jourdain, Anne; Peng, Lan; Phommahaxay, Alain; De Vos, Joeri; Rebibis, Kenneth June; Miller, Andy; Sleeckx, Erik; Beyne, Eric; Uedono, Akira

2017-05-01

Wafer-to-wafer three-dimensional (3D) integration with minimal Si thickness can produce interacting multiple devices with significantly scaled vertical interconnections. Realizing such a thin 3D structure, however, depends critically on the surface and subsurface of the remaining backside Si after the thinning processes. The Si (sub)surface after mechanical grinding has already been characterized fruitfully for a range of few dozen of μm. Here, we expand the characterization of Si (sub)surface to 5 μm thickness after thinning process on dielectric bonded wafers. The subsurface defects and damage layer were investigated after grinding, chemical mechanical polishing (CMP), wet etching and plasma dry etching. The (sub)surface defects were characterized using transmission microscopy, atomic force microscopy, and positron annihilation spectroscopy. Although grinding provides the fastest removal rate of Si, the surface roughness was not compatible with subsequent processing. Furthermore, mechanical damage such as dislocations and amorphous Si cannot be reduced regardless of Si thickness and thin wafer handling systems. The CMP after grinding showed excellent performance to remove this grinding damage, even though the removal amount is 1 μm. For the case of Si thinning towards 5 μm using grinding and CMP, the (sub)surface is atomic scale of roughness without vacancy. For the case of grinding + dry etch, vacancy defects were detected in subsurface around 0.5-2 μm. The finished surface after wet etch remains in the nm scale in the strain region. By inserting a CMP step in between grinding and dry etch it is possible to significantly reduce not only the roughness, but also the remaining vacancies at the subsurface. The surface of grinding + CMP + dry etching gives an equivalent mono vacancy result as to that of grinding + CMP. This combination of thinning processes allows development of extremely thin 3D integration devices with minimal roughness and vacancy surface.

Pathogen transport in groundwater systems: contrasts with traditional solute transport

NASA Astrophysics Data System (ADS)

Hunt, Randall J.; Johnson, William P.

2017-06-01

Water quality affects many aspects of water availability, from precluding use to societal perceptions of fit-for-purpose. Pathogen source and transport processes are drivers of water quality because they have been responsible for numerous outbreaks resulting in large economic losses due to illness and, in some cases, loss of life. Outbreaks result from very small exposure (e.g., less than 20 viruses) from very strong sources (e.g., trillions of viruses shed by a single infected individual). Thus, unlike solute contaminants, an acute exposure to a very small amount of contaminated water can cause immediate adverse health effects. Similarly, pathogens are larger than solutes. Thus, interactions with surfaces and settling become important even as processes important for solutes such as diffusion become less important. These differences are articulated in "Colloid Filtration Theory", a separate branch of pore-scale transport. Consequently, understanding pathogen processes requires changes in how groundwater systems are typically characterized, where the focus is on the leading edges of plumes and preferential flow paths, even if such features move only a very small fraction of the aquifer flow. Moreover, the relatively short survival times of pathogens in the subsurface require greater attention to very fast (<10 year) flow paths. By better understanding the differences between pathogen and solute transport mechanisms discussed here, a more encompassing view of water quality and source water protection is attained. With this more holistic view and theoretical understanding, better evaluations can be made regarding drinking water vulnerability and the relation between groundwater and human health.

RISK ASSESSMENT ANALYSES USING EPA'S ON-LINE SITE-SPECIFIC TRANSPORT MODELS AND FIELD DATA

EPA Science Inventory

EPA has developed a suite of on-line calculators and transport models to aid in risk assessment for subsurface contamination. The calculators (www.epa.gov/athens/onsite) provide several levels of tools and data. These include tools for generating commonly-used model input param...

Grand challenge problems in environmental modeling and remediation: groundwater contaminant transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Todd Arbogast; Steve Bryant; Clint N. Dawson

1998-08-31

This report describes briefly the work of the Center for Subsurface Modeling (CSM) of the University of Texas at Austin (and Rice University prior to September 1995) on the Partnership in Computational Sciences Consortium (PICS) project entitled Grand Challenge Problems in Environmental Modeling and Remediation: Groundwater Contaminant Transport.

Analytic solutions for colloid transport with time- or depth-dependent retention in porous media

USDA-ARS?s Scientific Manuscript database

Elucidating and quantifying the transport of industrial nanoparticles (e.g. silver, carbon nanotubes, and graphene oxide) and other colloid-size particles such as viruses and bacteria is important to safeguard and manage the quality of the subsurface environment. Analytic solutions were derived for...

EXPERIMENTAL EVALUATION OF TWO SHARP FRONT MODELS FOR VADOSE ZONE NON-AQUEOUS PHASE LIQUID TRANSPORT

EPA Science Inventory

Recent research efforts on the transport of immiscible organic wastes in subsurface the development of numerical models of various levels of sophistication. Systems have focused on the site characterization data needed to obtain. However, in real field applications, the model p...

Quantification of the Mass Transfer at Fluid Interfaces in Microfluidic Channels

NASA Astrophysics Data System (ADS)

Wismeth, Carina; Manhart, Michael; Niessner, Reinhard; Baumann, Thomas

2017-04-01

Mass transfer rates at interfaces in a complex porous media are relevant in many environmental applications and control the functions of natural filter systems in subsurface environments. The mass transfer at fluid interfaces is associated with interface convection caused by local inhomogeneities in interface tension and hydrodynamic instabilities at the interface. If there is a surface tension gradient along the surface a shear stress jump is generated that results in fluid motion along the surface that is called Marangoni effect. These spontaneous convection currents can lead to an increased mass transfer of the transition component at the phase boundary and to an increased mixing of the phases. Therefore compensatory currents at the interface can have a significant influence on the subsurface transport of contaminants in the groundwater area, especially in the vadose zone. Using microfluidic channels and advanced experimental techniques it is possible to measure the fluid flow and mass transfer rates directly and to quantify the effect of the Marangoni convection on the mass transfer at interfaces between a non-aqueous liquid and water with high temporal and spatial resolution. The use of fluorescent particles as well as the recording and analysis of their trajectories is intended to visualize interfacial processes and to quantify the mass transfer at fluid phase boundaries. Concentration gradients at the interface are analysed by spectroscopic methods and allow an assessment of the enrichment and depletion at the phase boundaries. Extensive test series provide the experimental basis for quantifying and analysing the impact of the Marangoni effect on the mass transfer rates at interfaces in porous media in subsurface aquatic environments. Within this research project we concentrate on the effect of Marangoni convection on the mass transfer near an 1-octanol-water interface, which serves as a well defined proxy for non-aqueous phase liquids in porous media. Experiments and a numerical simulation are closely coupled to provide a generic data set with high reproducibility and used to obtain highly resolved three-dimensional data of mass transfer in two- and three-phase systems to foster the understanding of subsurface transport, especially in the vadose zone.

Effect of Natural Abiotic Colloids on the Transport of Lindane (gamma-hexachlorocyclohexane) through Saturated Porous Media: Laboratory Experiments and Model-Based Analysis

NASA Astrophysics Data System (ADS)

Ngueleu Kamangou, S.; Cirpka, O. A.; Grathwohl, P.

2012-04-01

In many developing countries, the hygienic situation has improved by changing from surface-water bodies to groundwater as drinking water resource. However, failures have frequently been reported, presumably caused by wrong design of groundwater extraction (e.g., wells too close to open-water bodies, landfill leachates or agricultural areas). Moreover threat to groundwater pollution is enhanced when colloidal particles in the subsurface can act as carriers for adsorbing contaminants such as hydrophobic chlorinated organic contaminants. In this study, the main objective was to investigate the influence of particles in the size range of colloids on the subsurface transport of pesticides which are known to cause severe health problems. The model pesticide was gamma-hexachlorocyclohexane, a representative hydrophobic insecticide which is still used mainly in tropical countries. Colloid-facilitated transport was carried out by considering a first case where the adsorption of the contaminant to the particles is at equilibrium before getting simultaneously transported, and a second case where this equilibrium was not reached before their transport. Another focus besides colloid-facilitated transport was placed on the release of the contaminant from trapped colloids. Data analysis was done with the help of numerical modeling and the minimum model complexity needed to simulate such transports was examined.

A High-Resolution Model of Water Mass Transformation and Transport in the Weddell Sea

NASA Astrophysics Data System (ADS)

Hazel, J.; Stewart, A.

2016-12-01

The ocean circulation around the Antarctic margins has a pronounced impact on the global ocean and climate system. One of these impacts includes closing the global meridional overturning circulation (MOC) via formation of dense Antarctic Bottom Water (AABW), which ventilates a large fraction of the subsurface ocean. AABW is also partially composed of modified Circumpolar Deep Water (CDW), a warm, mid-depth water mass whose transport towards the continent has the potential to induce rapid retreat of marine-terminating glaciers. Previous studies suggest that these water mass exchanges may be strongly influenced by high-frequency processes such as downslope gravity currents, tidal flows, and mesoscale/submesoscale eddy transport. However, evaluating the relative contributions of these processes to near-Antarctic water mass transports is hindered by the region's relatively small scales of motion and the logistical difficulties in taking measurements beneath sea ice.In this study we develop a regional model of the Weddell Sea, the largest established source of AABW. The model is forced by an annually-repeating atmospheric state constructed from the Antarctic Mesoscale Prediction System data and by annually-repeating lateral boundary conditions constructed from the Southern Ocean State Estimate. The model incorporates the full Filchner-Ronne cavity and simulates the thermodynamics and dynamics of sea ice. To analyze the role of high-frequency processes in the transport and transformation of water masses, we compute the model's overturning circulation, water mass transformations, and ice sheet basal melt at model horizontal grid resolutions ranging from 1/2 degree to 1/24 degree. We temporally decompose the high-resolution (1/24 degree) model circulation into components due to mean, eddy and tidal flows and discuss the geographical dependence of these processes and their impact on water mass transformation and transport.

Influence of mineral colloids and humic substances on uranium(VI) transport in water-saturated geologic porous media

NASA Astrophysics Data System (ADS)

Wang, Qing; Cheng, Tao; Wu, Yang

2014-12-01

Mineral colloids and humic substances often co-exist in subsurface environment and substantially influence uranium (U) transport. However, the combined effects of mineral colloids and humic substances on U transport are not clear. This study is aimed at quantifying U transport and elucidating geochemical processes that control U transport when both mineral colloids and humic acid (HA) are present. U-spiked solutions/suspensions were injected into water-saturated sand columns, and U and colloid concentrations in column effluent were monitored. We found that HA promoted U transport via (i) formation of aqueous U-HA complexes, and (ii) competition against aqueous U for surface sites on transport media. Illite colloids had no influence on U transport at pH 5 in the absence of HA due to low mobility of the colloids. At pH 9, U desorbed from mobile illite and the presence of illite decreased U transport. At pH 5, high U transport occurred when both illite colloids and HA were present, which was attributed to enhanced U adsorption to illite colloids via formation of ternary illite-HA-U surface complexes, and enhanced illite transport due to HA attachment to illite and transport media. This study demonstrates that the combined effects of mineral colloids and HA on contaminant transport is different from simple addition of the individual effect.

Evaluation of a Genome-Scale In Silico Metabolic Model for Geobacter metallireducens Using Proteomic Data from a Field Biostimulation Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Yilin; Wilkins, Michael J.; Yabusaki, Steven B.

2012-12-12

Biomass and shotgun global proteomics data that reflected relative protein abundances from samples collected during the 2008 experiment at the U.S. Department of Energy Integrated Field-Scale Subsurface Research Challenge site in Rifle, Colorado, provided an unprecedented opportunity to validate a genome-scale metabolic model of Geobacter metallireducens and assess its performance with respect to prediction of metal reduction, biomass yield, and growth rate under dynamic field conditions. Reconstructed from annotated genomic sequence, biochemical, and physiological data, the constraint-based in silico model of G. metallireducens relates an annotated genome sequence to the physiological functions with 697 reactions controlled by 747 enzyme-coding genes.more » Proteomic analysis showed that 180 of the 637 G. metallireducens proteins detected during the 2008 experiment were associated with specific metabolic reactions in the in silico model. When the field-calibrated Fe(III) terminal electron acceptor process reaction in a reactive transport model for the field experiments was replaced with the genome-scale model, the model predicted that the largest metabolic fluxes through the in silico model reactions generally correspond to the highest abundances of proteins that catalyze those reactions. Central metabolism predicted by the model agrees well with protein abundance profiles inferred from proteomic analysis. Model discrepancies with the proteomic data, such as the relatively low fluxes through amino acid transport and metabolism, revealed pathways or flux constraints in the in silico model that could be updated to more accurately predict metabolic processes that occur in the subsurface environment.« less

A software tool to assess uncertainty in transient-storage model parameters using Monte Carlo simulations

USGS Publications Warehouse

Ward, Adam S.; Kelleher, Christa A.; Mason, Seth J. K.; Wagener, Thorsten; McIntyre, Neil; McGlynn, Brian L.; Runkel, Robert L.; Payn, Robert A.

2017-01-01

Researchers and practitioners alike often need to understand and characterize how water and solutes move through a stream in terms of the relative importance of in-stream and near-stream storage and transport processes. In-channel and subsurface storage processes are highly variable in space and time and difficult to measure. Storage estimates are commonly obtained using transient-storage models (TSMs) of the experimentally obtained solute-tracer test data. The TSM equations represent key transport and storage processes with a suite of numerical parameters. Parameter values are estimated via inverse modeling, in which parameter values are iteratively changed until model simulations closely match observed solute-tracer data. Several investigators have shown that TSM parameter estimates can be highly uncertain. When this is the case, parameter values cannot be used reliably to interpret stream-reach functioning. However, authors of most TSM studies do not evaluate or report parameter certainty. Here, we present a software tool linked to the One-dimensional Transport with Inflow and Storage (OTIS) model that enables researchers to conduct uncertainty analyses via Monte-Carlo parameter sampling and to visualize uncertainty and sensitivity results. We demonstrate application of our tool to 2 case studies and compare our results to output obtained from more traditional implementation of the OTIS model. We conclude by suggesting best practices for transient-storage modeling and recommend that future applications of TSMs include assessments of parameter certainty to support comparisons and more reliable interpretations of transport processes.

Annual subsurface transport of a red tide dinoflagellate to its bloom area: Water circulation patterns and organism distributions in the Chesapeake Bay

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tyler, M.A.; Seliger, H.H.

1978-03-01

An annual, long range, subsurface transport of Prorocentrum mariae-lebouriae, from the mouth of the Chesapeake Bay to its bloom area in the upper bay, a distance of 240 km, is described and completely documented. Prorocentrum in surface outflowing waters at the mouth of the bay is recruited in late winter into more dense inflowing coastal waters. Strong stratification produced by late winter--early spring surface runoff results in the development of a stable pycnocline. Prorocentrum, now in northward-flowing bottom waters, is retained in these bottom waters. It accumulates in a subsurface concentration maximum below the pycnocline and is transported northward tomore » reach its bloom area in the Patapsco River and north of the Bay Bridge by late spring. The rapidly decreasing depth of the upper bay causes the pycnocline to rise, mixing the previously light-limited Prorocentrum and its nutrient-rich bottom waters to the surface, where rapid growth ensues. Once the dinoflagellate is in surface waters, positive phototaxis, combined with both wind- and tide-driven surface convergences, produce dense surface patches or red tides. Prorocentrum is effectively retained in the bay until late winter by sequential inoculation into the tributary estuaries on the western shore, which exchange relatively slowly with bay waters. By late winter the annual cycle is complete. Prorocentrum is again in surface waters at the mouth of the bay where it is reintroduced into northward-flowing bottom waters. The mechanisms described provide a key to understanding the origins of subsurface chlorophyll maxima and the delivery of toxic dinoflagellates to coastal bloom areas.« less

Surface-Atmosphere Connections on Titan: A New Window into Terrestrial Hydroclimate

NASA Astrophysics Data System (ADS)

Faulk, Sean

This dissertation investigates the coupling between the large-scale atmospheric circulation and surface processes on Titan, with a particular focus on methane precipitation and its influence on surface geomorphology and hydrology. As the only body in the Solar System with an active hydrologic cycle other than Earth, Titan presents a valuable laboratory for studying principles of hydroclimate on terrestrial planets. Idealized general circulation models (GCMs) are used here to test hypotheses regarding Titan's surface-atmosphere connections. First, an Earth-like GCM simulated over a range of rotation rates is used to evaluate the effect of rotation rate on seasonal monsoon behavior. Slower rotation rates result in poleward migration of summer rain, indicating a large-scale atmospheric control on Titan's observed dichotomy of dry low latitudes and moist high latitudes. Second, a Titan GCM benchmarked against observations is used to analyze the magnitudes and frequencies of extreme methane rainstorms as simulated by the model. Regional patterns in these extreme events correlate well with observed geomorphic features, with the most extreme rainstorms occurring in mid-latitude regions associated with high alluvial fan concentrations. Finally, a planetary surface hydrology scheme is developed and incorporated into a Titan GCM to evaluate the roles of surface flow, subsurface flow, infiltration, and groundmethane evaporation in Titan's climate. The model reproduces Titan's observed surface liquid and cloud distributions, and reaches an equilibrium state with limited interhemispheric transport where atmospheric transport is approximately balanced by subsurface transport. The equilibrium state suggests that Titan's current hemispheric surface liquid asymmetry, favoring methane accumulation in the north, is stable in the modern climate.

Surface-subsurface turbulent interaction at the interface of a permeable bed: influence of the wall permeability

NASA Astrophysics Data System (ADS)

Kim, T.; Blois, G.; Best, J.; Christensen, K. T.

2017-12-01

Coarse-gravel river beds possess a high degree of permeability. Flow interactions between surface and subsurface flow across the bed interface is key to a number of natural processes occurring in the hyporheic zone. In fact, it is increasingly recognized that these interactions drive mass, momentum and energy transport across the interface, and consequently control biochemical processes as well as stability of sediments. The current study explores the role of the wall permeability in surface and subsurface flow interaction under controlled experimental conditions on a physical model of a gravel bed. The present wall model was constructed by five layers of cubically arranged spheres (d=25.4mm, where d is a diameter) providing 48% of porosity. Surface topography was removed by cutting half of a diameter on the top layer of spheres to render the flow surface smooth and highlight the impact of the permeability on the overlying flow. An impermeable smooth wall was also considered as a baseline of comparison for the permeable wall flow. To obtain basic flow statistics, low-frame-rate high-resolution PIV measurements were performed first in the streamwise-wall-normal (x-y) plane and refractive-index matching was employed to optically access the flow within the permeable wall. Time-resolved PIV experiments in the same facility were followed to investigate the flow interaction across the wall interface in sptaio-temporal domain. In this paper, a detailed analysis of the first and second order velocity statistics as well as the amplitude modulation for the flow overlying the permeable smooth wall will be presented.

Microbial community assembly patterns under incipient conditions in a basaltic soil system

NASA Astrophysics Data System (ADS)

Sengupta, A.; Stegen, J.; Alves Meira Neto, A.; Wang, Y.; Chorover, J.; Troch, P. A. A.; Maier, R. M.

2017-12-01

In sub-surface environments, the biotic components are critically linked to the abiotic processes. However, there is limited understanding of community establishment, functional associations, and community assembly processes of such microbes in sub-surface environments. This study presents the first analysis of microbial signatures in an incipient terrestrial basalt soil system conducted under controlled conditions. A sub-meter scale sampling of a soil mesocosm revealed the contrasting distribution patterns of simple soil parameters such as bulk density and electrical conductivity. Phylogenetic analysis of 16S rRNA gene indicated the presence of a total 40 bacterial and archaeal phyla, with high relative abundance of Actinobacteria on the surface and highest abundance of Proteobacteria throughout the system. Community diversity patterns were inferred to be dependent on depth profile and average water content in the system. Predicted functional gene analysis suggested mixotrophy lifestyles with both autotrophic and heterotrophic metabolisms, likelihood of a unique salt tolerant methanogenic pathway with links to novel Euryarchea, signatures of an incomplete nitrogen cycle, and predicted enzymes of extracellular iron (II) to iron (III) conversion followed by intracellular uptake, transport and regulation. Null modeling revealed microbial community assembly was predominantly governed by variable selection, but the influence of the variable selection did not show systematic spatial structure. The presence of significant heterogeneity in predicted functions and ecologically deterministic shifts in community composition in a homogeneous incipient basalt highlights the complexity exhibited by microorganisms even in the simplest of environmental systems. This presents an opportunity to further develop our understanding of how microbial communities establish, evolve, impact, and respond in sub-surface environments.

Trace Element and Cu Isotopic Tracers of Subsurface Flow and Transport in Wastewater Irrigated Soils

NASA Astrophysics Data System (ADS)

Carte, J.; Fantle, M. S.

2017-12-01

An understanding of subsurface flow paths is critical for quantifying the fate of contaminants in wastewater irrigation systems. This study investigates the subsurface flow of wastewater by quantifying the distribution of trace contaminants in wastewater irrigated soils. Soil samples were collected from the upper 1m of two wetlands at Penn State University's wastewater irrigation site, at which all effluent from the University's wastewater treatment plant has been sprayed since 1983. Major and trace element and Cu isotopic composition were determined for these samples, in addition to wastewater effluent and bedrock samples. The upper 20 cm of each wetland shows an enrichment of Bi, Cd, Cr, Cu, Mo, Ni, Pb, and Zn concentrations relative to deep (>1m) soils at the site by a factor of 1.7-3.5. Each wetland also has a subsurface clay rich horizon with Bi, Cu, Li, Ni, Pb, and Zn concentrations enriched by a factor of 1.4 to 5 relative to deep soils. These subsurface horizons directly underlie intervals that could facilitate preferential effluent flow: a gravel layer in one wetland, and a silty loam with visible mottling, an indication of dynamic water saturation, in the other. Trace metal concentrations in other horizons from both wetlands fall in the range of the deep soils. Significant variability in Cu isotopic composition is present in soils from both wetlands, with δ65Cu values ranging from 0.74‰ to 5.09‰. Soil δ65Cu correlates well with Cu concentrations, with lighter δ65Cu associated with higher concentrations. The Cu isotopic composition of the zones of metal enrichment are comparable to the ostensible average wastewater effluent δ65Cu value (0.61‰), while other horizons have considerably heavier δ65Cu values. We hypothesize that wastewater is the source of the metal enrichments, as each of the enriched elements are present as contaminants in wastewater, and the enrichments are located in clay-rich horizons conducive to trace metal immobilization due to adsorption. This hypothesis will be further tested by modeling with the reactive transport code CrunchTope. This study provides evidence that trace element and isotopic composition of soils can be useful tracers of subsurface hydrologic pathways and elemental fate and transport.

Depth dependency of neutron density produced by cosmic rays in the lunar subsurface

NASA Astrophysics Data System (ADS)

Ota, S.; Sihver, L.; Kobayashi, S.; Hasebe, N.

2014-11-01

Depth dependency of neutrons produced by cosmic rays (CRs) in the lunar subsurface was estimated using the three-dimensional Monte Carlo particle and heavy ion transport simulation code, PHITS, incorporating the latest high energy nuclear data, JENDL/HE-2007. The PHITS simulations of equilibrium neutron density profiles in the lunar subsurface were compared with the measurement by Apollo 17 Lunar Neutron Probe Experiment (LNPE). Our calculations reproduced the LNPE data except for the 350-400 mg/cm2 region under the improved condition using the CR spectra model based on the latest observations, well-tested nuclear interaction models with systematic cross section data, and JENDL/HE-2007.

Thermal Methods for Investigating Ground-Water Recharge

USGS Publications Warehouse

Blasch, Kyle W.; Constantz, Jim; Stonestrom, David A.

2007-01-01

Recharge of aquifers within arid and semiarid environments is defined as the downward flux of water across the regional water table. The introduction of recharging water at the land surface can occur at discreet locations, such as in stream channels, or be distributed over the landscape, such as across broad interarroyo areas within an alluvial ground-water basin. The occurrence of recharge at discreet locations is referred to as focused recharge, whereas the occurrence of recharge over broad regions is referred to as diffuse recharge. The primary interest of this appendix is focused recharge, but regardless of the type of recharge, estimation of downward fluxes is essential to its quantification. Like chemical tracers, heat can come from natural sources or be intentionally introduced to infer transport properties and aquifer recharge. The admission and redistribution of heat from natural processes such as insolation, infiltration, and geothermal activity can be used to quantify subsurface flow regimes. Heat is well suited as a ground-water tracer because it provides a naturally present dynamic signal and is relatively harmless over a useful range of induced perturbations. Thermal methods have proven valuable for recharge investigations for several reasons. First, theoretical descriptions of coupled water-and-heat transport are available for the hydrologic processes most often encountered in practice. These include land-surface mechanisms such as radiant heating from the sun, radiant cooling into space, and evapotranspiration, in addition to the advective and conductive mechanisms that usually dominate at depth. Second, temperature is theoretically well defined and readily measured. Third, thermal methods for depths ranging from the land surface to depths of hundreds of meters are based on similar physical principles. Fourth, numerical codes for simulating heat and water transport have become increasingly reliable and widely available. Direct measurement of water flux in the subsurface is difficult, prompting investigators to pursue indirect methods. Geophysical approaches that exploit the coupled relation between heat and water transport provide an attractive class of methods that have become widely used in investigations of recharge. This appendix reviews the application of heat to the problem of recharge estimation. Its objective is to provide a fairly complete account of the theoretical underpinnings together with a comprehensive review of thermal methods in practice. Investigators began using subsurface temperatures to delineate recharge areas and infer directions of ground-water flow around the turn of the 20th century. During the 1960s, analytical and numerical solutions for simplified heat- and fluid-flow problems became available. These early solutions, though one-dimensional and otherwise restricted, provided a strong impetus for applying thermal methods to problems of liquid and vapor movement in systems ranging from soils to geothermal reservoirs. Today?s combination of fast processors, massive data-storage units, and efficient matrix techniques provide numerical solutions to complex, three-dimensional transport problems. These approaches allow researchers to take advantage of the considerable information content routinely achievable in high-accuracy temperature work.

A Multi-Scale, Integrated Approach to Representing Watershed Systems

NASA Astrophysics Data System (ADS)

Ivanov, Valeriy; Kim, Jongho; Fatichi, Simone; Katopodes, Nikolaos

2014-05-01

Understanding and predicting process dynamics across a range of scales are fundamental challenges for basic hydrologic research and practical applications. This is particularly true when larger-spatial-scale processes, such as surface-subsurface flow and precipitation, need to be translated to fine space-time scale dynamics of processes, such as channel hydraulics and sediment transport, that are often of primary interest. Inferring characteristics of fine-scale processes from uncertain coarse-scale climate projection information poses additional challenges. We have developed an integrated model simulating hydrological processes, flow dynamics, erosion, and sediment transport, tRIBS+VEGGIE-FEaST. The model targets to take the advantage of the current generation of wealth of data representing watershed topography, vegetation, soil, and landuse, as well as to explore the hydrological effects of physical factors and their feedback mechanisms over a range of scales. We illustrate how the modeling system connects precipitation-hydrologic runoff partition process to the dynamics of flow, erosion, and sedimentation, and how the soil's substrate condition can impact the latter processes, resulting in a non-unique response. We further illustrate an approach to using downscaled climate change information with a process-based model to infer the moments of hydrologic variables in future climate conditions and explore the impact of climate information uncertainty.

Development of Pflotran Code for Waste Isolation Pilot Plant Performance Assessment

NASA Astrophysics Data System (ADS)

Zeitler, T.; Day, B. A.; Frederick, J.; Hammond, G. E.; Kim, S.; Sarathi, R.; Stein, E.

2017-12-01

The Waste Isolation Pilot Plant (WIPP) has been developed by the U.S. Department of Energy (DOE) for the geologic (deep underground) disposal of transuranic (TRU) waste. Containment of TRU waste at the WIPP is regulated by the U.S. Environmental Protection Agency (EPA). The DOE demonstrates compliance with the containment requirements by means of performance assessment (PA) calculations. WIPP PA calculations estimate the probability and consequence of potential radionuclide releases from the repository to the accessible environment for a regulatory period of 10,000 years after facility closure. The long-term performance of the repository is assessed using a suite of sophisticated computational codes. There is a current effort to enhance WIPP PA capabilities through the further development of the PFLOTRAN software, a state-of-the-art massively parallel subsurface flow and reactive transport code. Benchmark testing of the individual WIPP-specific process models implemented in PFLOTRAN (e.g., gas generation, chemistry, creep closure, actinide transport, and waste form) has been performed, including results comparisons for PFLOTRAN and existing WIPP PA codes. Additionally, enhancements to the subsurface hydrologic flow mode have been made. Repository-scale testing has also been performed for the modified PFLTORAN code and detailed results will be presented. Ultimately, improvements to the current computational environment will result in greater detail and flexibility in the repository model due to a move from a two-dimensional calculation grid to a three-dimensional representation. The result of the effort will be a state-of-the-art subsurface flow and transport capability that will serve WIPP PA into the future for use in compliance recertification applications (CRAs) submitted to the EPA. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. This research is funded by WIPP programs administered by the Office of Environmental Management (EM) of the U.S. Department of Energy.SAND2017-8198A.

Viability of modelling gas transport in shallow injection-monitoring experiment field at Maguelone, France

NASA Astrophysics Data System (ADS)

Basirat, Farzad; Perroud, Hervé; Lofi, Johanna; Denchik, Nataliya; Lods, Gérard; Fagerlund, Fritjof; Sharma, Prabhakar; Pezard, Philippe; Niemi, Auli

2015-04-01

In this study, TOUGH2/EOS7CA model is used to simulate the shallow injection-monitoring experiment carried out at Maguelone, France, during 2012 and 2013. The possibility of CO2 leakage from storage reservoir to upper layers is one of the issues that need to be addressed in CCS projects. Developing reliable monitoring techniques to detect and characterize CO2 leakage is necessary for the safety of CO2 storage in reservoir formations. To test and cross-validate different monitoring techniques, a series of shallow gas injection-monitoring experiments (SIMEx) has been carried out at the Maguelone. The experimental site is documented in Lofi et al [2013]. At the site, a series of nitrogen and one CO2 injection experiment have been carried out during 2012-2013 and different monitoring techniques have been applied. The purpose of modelling is to acquire understanding of the system performance as well as to further develop and validate modelling approaches for gas transport in the shallow subsurface, against the well-controlled data sets. The preliminary simulation of the experiment including the simulation for the Nitrogen injection test in 2012 was presented in Basirat et al [2013]. In this work, the simulations represent the gaseous CO2 distribution and dissolved CO2 within range obtained by monitoring approaches. The Multiphase modelling in combination with geophysical monitoring can be used for process understanding of gas phase migration- and mass transfer processes resulting from gaseous CO2 injection. Basirat, F., A. Niemi, H. Perroud, J. Lofi, N. Denchik, G. Lods, P. Pezard, P. Sharma, and F. Fagerlund (2013), Modeling Gas Transport in the Shallow Subsurface in Maguelone Field Experiment, Energy Procedia, 40, 337-345. Lofi, J., P. Pezard, F. Bouchette, O. Raynal, P. Sabatier, N. Denchik, A. Levannier, L. Dezileau, and R. Certain (2013), Integrated Onshore-Offshore Investigation of a Mediterranean Layered Coastal Aquifer, Groundwater, 51(4), 550-561.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gutierrez, Marte

Colorado School of Mines conducted research and training in the development and validation of an advanced CO{sub 2} GS (Geological Sequestration) probabilistic simulation and risk assessment model. CO{sub 2} GS simulation and risk assessment is used to develop advanced numerical simulation models of the subsurface to forecast CO2 behavior and transport; optimize site operational practices; ensure site safety; and refine site monitoring, verification, and accounting efforts. As simulation models are refined with new data, the uncertainty surrounding the identified risks decrease, thereby providing more accurate risk assessment. The models considered the full coupling of multiple physical processes (geomechanical and fluidmore » flow) and describe the effects of stochastic hydro-mechanical (H-M) parameters on the modeling of CO{sub 2} flow and transport in fractured porous rocks. Graduate students were involved in the development and validation of the model that can be used to predict the fate, movement, and storage of CO{sub 2} in subsurface formations, and to evaluate the risk of potential leakage to the atmosphere and underground aquifers. The main major contributions from the project include the development of: 1) an improved procedure to rigorously couple the simulations of hydro-thermomechanical (H-M) processes involved in CO{sub 2} GS; 2) models for the hydro-mechanical behavior of fractured porous rocks with random fracture patterns; and 3) probabilistic methods to account for the effects of stochastic fluid flow and geomechanical properties on flow, transport, storage and leakage associated with CO{sub 2} GS. The research project provided the means to educate and train graduate students in the science and technology of CO{sub 2} GS, with a focus on geologic storage. Specifically, the training included the investigation of an advanced CO{sub 2} GS simulation and risk assessment model that can be used to predict the fate, movement, and storage of CO{sub 2} in underground formations, and the evaluation of the risk of potential CO{sub 2} leakage to the atmosphere and underground aquifers.« less

Machine learning to construct reduced-order models and scaling laws for reactive-transport applications

NASA Astrophysics Data System (ADS)

Mudunuru, M. K.; Karra, S.; Vesselinov, V. V.

2017-12-01

The efficiency of many hydrogeological applications such as reactive-transport and contaminant remediation vastly depends on the macroscopic mixing occurring in the aquifer. In the case of remediation activities, it is fundamental to enhancement and control of the mixing through impact of the structure of flow field which is impacted by groundwater pumping/extraction, heterogeneity, and anisotropy of the flow medium. However, the relative importance of these hydrogeological parameters to understand mixing process is not well studied. This is partially because to understand and quantify mixing, one needs to perform multiple runs of high-fidelity numerical simulations for various subsurface model inputs. Typically, high-fidelity simulations of existing subsurface models take hours to complete on several thousands of processors. As a result, they may not be feasible to study the importance and impact of model inputs on mixing. Hence, there is a pressing need to develop computationally efficient models to accurately predict the desired QoIs for remediation and reactive-transport applications. An attractive way to construct computationally efficient models is through reduced-order modeling using machine learning. These approaches can substantially improve our capabilities to model and predict remediation process. Reduced-Order Models (ROMs) are similar to analytical solutions or lookup tables. However, the method in which ROMs are constructed is different. Here, we present a physics-informed ML framework to construct ROMs based on high-fidelity numerical simulations. First, random forests, F-test, and mutual information are used to evaluate the importance of model inputs. Second, SVMs are used to construct ROMs based on these inputs. These ROMs are then used to understand mixing under perturbed vortex flows. Finally, we construct scaling laws for certain important QoIs such as degree of mixing and product yield. Scaling law parameters dependence on model inputs are evaluated using cluster analysis. We demonstrate application of the developed method for model analyses of reactive-transport and contaminant remediation at the Los Alamos National Laboratory (LANL) chromium contamination sites. The developed method is directly applicable for analyses of alternative site remediation scenarios.

Application of a pore-scale reactive transport model to a natural analog for reaction-induced pore alterations

DOE PAGES

Yoon, Hongkyu; Major, Jonathan; Dewers, Thomas; ...

2017-01-05

Dissolved CO 2 in the subsurface resulting from geological CO 2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes including hydrodynamics, transport, and reactions at the (sub) pore-scale. In this work pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reactions at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This paper is motivated by observations of CO 2 seeps from a natural CO 2 sequestration analog, Crystal Geyser, Utah. Observations alongmore » the surface exposure of the Little Grand Wash fault indicate the lateral migration of CO 2 seep sites (i.e., alteration zones) of 10–50 m width with spacing on the order of ~100 m over time. Sandstone permeability in alteration zones is reduced by 3–4 orders of magnitude by carbonate cementation compared to unaltered zones. One granular porous medium and one fracture network systems are used to conceptually represent permeable porous media and locations of conduits controlled by fault-segment intersections and/or topography, respectively. Simulation cases accounted for a range of reaction regimes characterized by the Damköhler (Da) and Peclet (Pe) numbers. Pore-scale simulation results demonstrate that combinations of transport (Pe), geochemical conditions (Da), solution chemistry, and pore and fracture configurations contributed to match key patterns observed in the field of how calcite precipitation alters flow paths by pore plugging. This comparison of simulation results with field observations reveals mechanistic explanations of the lateral migration and enhances our understanding of subsurface processes associated with the CO 2 injection. In addition, permeability and porosity relations are constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Da and Pe numbers. Finally, the functional relationships obtained from pore-scale simulations can be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO 2 seeps.« less

Soil Segregation Methods for Reducing Transportation and Disposal Costs - 13544

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frothingham, David; Andrews, Shawn; Barker, Michelle

2013-07-01

At Formerly Utilized Sites Remedial Action Program (FUSRAP) sites where the selected alternative for contaminated soil is excavation and off-site disposal, the most significant budget items of the remedial action are the costs for transportation and disposal of soil at an off-site facility. At these sites, the objective is to excavate and dispose of only those soils that exceed derived concentration guideline levels. In situ soil segregation using gross gamma detectors to guide the excavation is often challenging at sites where the soil contamination is overlain by clean soil or where the contaminated soil is located in isolated, subsurface pockets.more » In addition, data gaps are often identified during the alternative evaluation and selection process, resulting in increased uncertainty in the extent of subsurface contamination. In response, the U.S. Army Corps of Engineers, Buffalo District is implementing ex situ soil segregation methods. At the remediated Painesville Site, soils were excavated and fed through a conveyor-belt system, which automatically segregated them into above- and below-cleanup criteria discharge piles utilizing gamma spectroscopy. At the Linde Site and the Shallow Land Disposal Area (SLDA) Site, which are both in the remediation phase, soils are initially segregated during the excavation process using gross gamma detectors and then transported to a pad for confirmatory manual surveying and sampling. At the Linde Site, the ex situ soils are analyzed on the basis of a site-specific method, to establish compliance with beneficial reuse criteria that were developed for the Linde remediation. At the SLDA Site, the ex situ soils are surveyed and sampled based on Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) final status survey guidance to demonstrate compliance with the derived concentration guideline levels. At all three sites, the ex situ soils that meet the site- specific DCGLs are retained on-site and used as backfill material. This paper describes the ex situ soil segregation methods, the considerations of each method, and the estimated cost savings from minimizing the volume of soil requiring transportation and off-site disposal. (authors)« less

Study of heavy metals transport by runoff and sediments from an abandoned mine: Alagoa, Portugal

NASA Astrophysics Data System (ADS)

Gerardo, R.; de Lima, J. L. M. P.; de Lima, M. I. P.

2009-04-01

Over time, several studies have been designed to understand heavy metals fate and its impact on the environment and on human health. However, only a few studies have focused on the transport of heavy metals in mining areas through the various hydrological processes such as runoff, infiltration, and subsurface flow. In particular, heavy rainfall events have a great impact on the dispersion of metals existing in the soil. This problem is often more serious in abandoned and inactive mining sites causing environmental problems. In Portugal, there are 175 identified abandoned mines that continuously threaten the environment through acid drainage waters that pollute the soil as well as surface and groundwater. An example is the abandoned mine of Alagoa, located near the village of Penacova (Centre of Portugal); in this site mining activities ceased about 30 years ago. The area is characterized by very steep slopes that are confining with a small stream; the mining excavation by-products were deposited on these slopes. We have selected this mine as a case study, aiming at understanding the transport mechanisms and dispersion of heavy metals and at contributing to the definition of the most appropriate mitigation measures for this area that is contaminated by heavy metals from the mine tailings. So far a total of 30 soil samples from 3 contaminated zones were collected and analysed for pH, texture and heavy metal content, using atomic absorption spectroscopy. Results indicate that the contents of Zn and Pb in the soil samples are in the range from 95-460 mg/kg and 67-239 mg/kg, respectively, which exceed the critical limit-values defined by the Portuguese legislation. These metals are dispersed downslope and downstream from the mine tailings by storm water. The next step of this work is to investigate the transport of heavy metals by runoff, by mobilization of sediments and by subsurface flow. Three spatial scales tests will be conducted: on the mine tailings, on the slope areas, and in the laboratory, using soil flumes, which include the use of rainfall simulators. This study will allow the evaluation of several variables and processes, described above, under controlled conditions.

Depth-discrete sampling port

DOEpatents

Pemberton, Bradley E [Aiken, SC; May, Christopher P [Columbia, MD; Rossabi, Joseph [Aiken, SC; Riha, Brian D [Augusta, GA; Nichols, Ralph L [North Augusta, SC

1998-07-07

A sampling port is provided which has threaded ends for incorporating the port into a length of subsurface pipe. The port defines an internal receptacle which is in communication with subsurface fluids through a series of fine filtering slits. The receptacle is in further communication through a bore with a fitting carrying a length of tubing there which samples are transported to the surface. Each port further defines an additional bore through which tubing, cables, or similar components of adjacent ports may pass.

Depth-discrete sampling port

DOEpatents

Pemberton, Bradley E.; May, Christopher P.; Rossabi, Joseph; Riha, Brian D.; Nichols, Ralph L.

1999-01-01

A sampling port is provided which has threaded ends for incorporating the port into a length of subsurface pipe. The port defines an internal receptacle which is in communication with subsurface fluids through a series of fine filtering slits. The receptacle is in further communication through a bore with a fitting carrying a length of tubing there which samples are transported to the surface. Each port further defines an additional bore through which tubing, cables, or similar components of adjacent ports may pass.

Fate and Transport of Tungsten at Camp Edwards Small Arms Ranges

DTIC Science & Technology

2007-08-01

area into the lower berm and/or trough. A similar approach was used in the lower berm area with samples collected from soil sloughing from the...bucket au- ger to collect samples beneath the bullet pockets and the trough. A multi - increment, subsurface soil sample was made by combining the...range. From these soil profiles, a total of 72 multi -increment subsurface soil sam- ples was collected (Table 2). The auger was cleaned between holes

Evaluating permafrost thaw vulnerabilities and hydrologic impacts in boreal Alaska (USA) watersheds using field data and cryohydrogeologic modeling

NASA Astrophysics Data System (ADS)

Walvoord, M. A.; Voss, C.; Ebel, B. A.; Minsley, B. J.

2017-12-01

Permafrost environments undergo changes in hydraulic, thermal, chemical, and mechanical subsurface properties upon thaw. These property changes must be considered in addition to alterations in hydrologic, thermal, and topographic boundary conditions when evaluating shifts in the movement and storage of water in arctic and sub-arctic boreal regions. Advances have been made in the last several years with respect to multiscale geophysical characterization of the subsurface and coupled fluid and energy transport modeling of permafrost systems. Ongoing efforts are presented that integrate field data with cryohydrogeologic modeling to better understand and anticipate changes in subsurface water resources, fluxes, and flowpaths caused by climate warming and permafrost thawing. Analyses are based on field data from several sites in interior Alaska (USA) that span a broad north-south transition from continuous to discontinuous permafrost. These data include soil hydraulic and thermal properties and shallow permafrost distribution. The data guide coupled fluid and energy flow simulations that incorporate porewater liquid/ice phase change and the accompanying modifications in hydraulic and thermal subsurface properties. Simulations are designed to assess conditions conducive to active layer thickening and talik development, both of which are expected to affect groundwater storage and flow. Model results provide a framework for identifying factors that control the rates of permafrost thaw and associated hydrologic responses, which in turn influence the fate and transport of carbon.

Fracturing And Liquid CONvection

DOE Office of Scientific and Technical Information (OSTI.GOV)

2012-02-29

FALCON has been developed to enable simulation of the tightly coupled fluid-rock behavior in hydrothermal and engineered geothermal system (EGS) reservoirs, targeting the dynamics of fracture stimulation, fluid flow, rock deformation, and heat transport in a single integrated code, with the ultimate goal of providing a tool that can be used to test the viability of EGS in the United States and worldwide. Reliable reservoir performance predictions of EGS systems require accurate and robust modeling for the coupled thermal-hydrological-mechanical processes. Conventionally, these types of problems are solved using operator-splitting methods, usually by coupling a subsurface flow and heat transport simulatormore » with a solid mechanics simulator via input files. FALCON eliminates the need for using operator-splitting methods to simulate these systems, and the scalability of the underlying MOOSE architecture allows for simulating these tightly coupled processes at the reservoir scale, allowing for examination of the system as a whole (something the operator-splitting methodologies generally cannot do).« less

Effect of Agricultural Practices on Hydrology and Water Chemistry in a Small Irrigated Catchment, Yakima River Basin, Washington

USGS Publications Warehouse

McCarthy, Kathleen A.; Johnson, Henry M.

2009-01-01

The role of irrigation and artificial drainage in the hydrologic cycle and the transport of solutes in a small agricultural catchment in central Washington's Yakima Valley were explored using hydrologic, chemical, isotopic, age-dating, and mineralogical data from several environmental compartments, including stream water, ground water, overland flow, and streambed pore water. A conceptual understanding of catchment hydrology and solute transport was developed and an inverse end-member mixing analysis was used to further explore the effects of agriculture in this small catchment. The median concentrations of major solutes and nitrates were similar for the single field site and for the catchment outflow site, indicating that the net effects of transport processes for these constituents were similar at both scales. However, concentrations of nutrients were different at the two sites, suggesting that field-scale variations in agricultural practices as well as nearstream and instream biochemical processes are important components of agricultural chemical transformation and transport in this catchment. This work indicates that irrigation coupled with artificial drainage networks may exacerbate the ecological effects of agricultural runoff by increasing direct connectivity between fields and streams and minimizing potentially mitigating effects (denitrification and dilution, for example) of longer subsurface pathways.

Development of Modeling Methods and Tools for Predicting Coupled Reactive Transport Processes in Porous Media at Multiple Scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clement, T. Prabhakar; Barnett, Mark O.; Zheng, Chunmiao

DE-FG02-06ER64213: Development of Modeling Methods and Tools for Predicting Coupled Reactive Transport Processes in Porous Media at Multiple Scales Investigators: T. Prabhakar Clement (PD/PI) and Mark O. Barnett (Auburn), Chunmiao Zheng (Univ. of Alabama), and Norman L. Jones (BYU). The objective of this project was to develop scalable modeling approaches for predicting the reactive transport of metal contaminants. We studied two contaminants, a radioactive cation [U(VI)] and a metal(loid) oxyanion system [As(III/V)], and investigated their interactions with two types of subsurface materials, iron and manganese oxyhydroxides. We also developed modeling methods for describing the experimental results. Overall, the project supportedmore » 25 researchers at three universities. Produced 15 journal articles, 3 book chapters, 6 PhD dissertations and 6 MS theses. Three key journal articles are: 1) Jeppu et al., A scalable surface complexation modeling framework for predicting arsenate adsorption on goethite-coated sands, Environ. Eng. Sci., 27(2): 147-158, 2010. 2) Loganathan et al., Scaling of adsorption reactions: U(VI) experiments and modeling, Applied Geochemistry, 24 (11), 2051-2060, 2009. 3) Phillippi, et al., Theoretical solid/solution ratio effects on adsorption and transport: uranium (VI) and carbonate, Soil Sci. Soci. of America, 71:329-335, 2007« less

Using digital databases to create geologic maps for the 21st century : a GIS model for geologic, environmental, cultural and transportation data from southern Rhode Island

DOT National Transportation Integrated Search

2002-05-01

Knowledge of surface and subsurface geology is fundamental to the planning and development of new or modified transportation systems. Toward this : end, we have compiled a model GIS database consisting of important geologic, cartographic, environment...

Effect of variable annual precipitation and nutrient input on nitrogen and phosphorus transport from two Midwestern agricultural watersheds

USDA-ARS?s Scientific Manuscript database

Precipitation patterns and nutrient inputs impact transport of nitrate (NO3-N) and phosphorus (TP) from Midwest watersheds. Nutrient concentrations and yields from two subsurface-drained watersheds, the Little Cobb River (LCR) in southern Minnesota and the South Fork Iowa River (SFIR) in northern Io...

Performance of dentrification beds for removing nitrate from drainage water at cold temperatures

USDA-ARS?s Scientific Manuscript database

Transport of soluble nitrogen and phosphorus to water bodies has been a concern for many years due to human health issues, and is a major contributor to the formation of oxygen deficiency in aquatic ecosystems. Agricultural subsurface drainage is one pathway for transport of excess nutrients to surf...

THE DOE COMPLEX-WIDE VADOSE ZONE SCIENCE AND TECHNOLOGY ROADMAP: CHARACTERIZATION MODELING AND SIMULATION OF SUBSURFACE CONTAMINANT FATE AND TRANSPORT

EPA Science Inventory

The Idaho National Engineering & Environmental Lab (INEEL) was charged by DOE EM to develop a complex-wide science and technology roadmap for the characterization, modeling and simulation of the fate and transport of contamination in the vadose zone. Various types of hazardous, r...

Enhanced transport of biodegradable polymer-coated nanoiron particles in sand columns

NASA Astrophysics Data System (ADS)

Jung, B.; O'Carroll, D.; Sleep, B.

2009-05-01

The use of nanoscale zerovalent iron has shown promise as a technology for remediation of subsurface contamination by chlorinated solvents. However, the delivery of nanoiron particles to target contaminated subsurface zones is hindered by the aggregation of particles due to magnetic attraction. To overcome the limitations of aggregation and increase nanoiron mobility in porous media, nanoiron particles have been coated with various polymers. Polymer adsorption onto nanoiron particles provides electrosteric stabilization, increases the mobility, and decreases the attachment onto the soil surface. Various polymers were investigated in this study, including carboxylmethyl cellulose (CMC) and guar gum, both of which are biodegradable. In sand column experiments the transport of nanoiron particles was investigated as a function of type of electrolyte, ionic strength, flow velocity, and nanoiron particle concentration. Settling curves showed the enhanced stability of polymer-coated nanoiron particles compared to bare commercial nanoiron particles (bare RNIP-10DS). A newly developed nanoparticle transport numerical model was used to quantify the attachment efficiency, as well as investigate dominant nanoparticle transport and removal mechanisms. Finally the particle-collector interaction energy was predicted using DLVO (Derjaguin-Landau-Verwey-Overbeek) theory.

Sensitivity analyses of a colloid-facilitated contaminant transport model for unsaturated heterogeneous soil conditions.

NASA Astrophysics Data System (ADS)

Périard, Yann; José Gumiere, Silvio; Rousseau, Alain N.; Caron, Jean

2013-04-01

Certain contaminants may travel faster through soils when they are sorbed to subsurface colloidal particles. Indeed, subsurface colloids may act as carriers of some contaminants accelerating their translocation through the soil into the water table. This phenomenon is known as colloid-facilitated contaminant transport. It plays a significant role in contaminant transport in soils and has been recognized as a source of groundwater contamination. From a mechanistic point of view, the attachment/detachment of the colloidal particles from the soil matrix or from the air-water interface and the straining process may modify the hydraulic properties of the porous media. Šimůnek et al. (2006) developed a model that can simulate the colloid-facilitated contaminant transport in variably saturated porous media. The model is based on the solution of a modified advection-dispersion equation that accounts for several processes, namely: straining, exclusion and attachement/detachement kinetics of colloids through the soil matrix. The solutions of these governing, partial differential equations are obtained using a standard Galerkin-type, linear finite element scheme, implemented in the HYDRUS-2D/3D software (Šimůnek et al., 2012). Modeling colloid transport through the soil and the interaction of colloids with the soil matrix and other contaminants is complex and requires the characterization of many model parameters. In practice, it is very difficult to assess actual transport parameter values, so they are often calibrated. However, before calibration, one needs to know which parameters have the greatest impact on output variables. This kind of information can be obtained through a sensitivity analysis of the model. The main objective of this work is to perform local and global sensitivity analyses of the colloid-facilitated contaminant transport module of HYDRUS. Sensitivity analysis was performed in two steps: (i) we applied a screening method based on Morris' elementary effects and the one-at-a-time approach (O.A.T); and (ii), we applied Sobol's global sensitivity analysis method which is based on variance decompositions. Results illustrate that ψm (maximum sorption rate of mobile colloids), kdmc (solute desorption rate from mobile colloids), and Ks (saturated hydraulic conductivity) are the most sensitive parameters with respect to the contaminant travel time. The analyses indicate that this new module is able to simulate the colloid-facilitated contaminant transport. However, validations under laboratory conditions are needed to confirm the occurrence of the colloid transport phenomenon and to understand model prediction under non-saturated soil conditions. Future work will involve monitoring of the colloidal transport phenomenon through soil column experiments. The anticipated outcome will provide valuable information on the understanding of the dominant mechanisms responsible for colloidal transports, colloid-facilitated contaminant transport and, also, the colloid detachment/deposition processes impacts on soil hydraulic properties. References: Šimůnek, J., C. He, L. Pang, & S. A. Bradford, Colloid-Facilitated Solute Transport in Variably Saturated Porous Media: Numerical Model and Experimental Verification, Vadose Zone Journal, 2006, 5, 1035-1047 Šimůnek, J., M. Šejna, & M. Th. van Genuchten, The C-Ride Module for HYDRUS (2D/3D) Simulating Two-Dimensional Colloid-Facilitated Solute Transport in Variably-Saturated Porous Media, Version 1.0, PC Progress, Prague, Czech Republic, 45 pp., 2012.

A field evaluation of subsurface and surface runoff. II. Runoff processes

USGS Publications Warehouse

Pilgrim, D.H.; Huff, D.D.; Steele, T.D.

1978-01-01

Combined use of radioisotope tracer, flow rate, specific conductance and suspended-sediment measurements on a large field plot near Stanford, California, has provided more detailed information on surface and subsurface storm runoff processes than would be possible from any single approach used in isolation. Although the plot was surficially uniform, the runoff processes were shown to be grossly nonuniform, both spatially over the plot, and laterally and vertically within the soil. The three types of processes that have been suggested as sources of storm runoff (Horton-type surface runoff, saturated overland flow, and rapid subsurface throughflow) all occurred on the plot. The nonuniformity of the processes supports the partial- and variable-source area concepts. Subsurface storm runoff occurred in a saturated layer above the subsoil horizon, and short travel times resulted from flow through macropores rather than the soil matrix. Consideration of these observations would be necessary for physically realistic modeling of the storm runoff process. ?? 1978.

Emerging Methods in Sub Core-Scale Imaging and Characterization of the Influence of Heterogeneity on Flow in Rocks (Invited)

NASA Astrophysics Data System (ADS)

Benson, S. M.; Hingerl, F.; Pini, R.

2013-12-01

New imaging techniques and approaches are providing unparalleled insight into the influence of sub-core scale heterogeneities on single and multiphase flows. Quantification of sub core-scale porosity, permeability, and even capillary pressure curves at a spatial scale of about 1-10 cubic millimeters is now possible. This scale provides a critical link in the continuum of spatial scales needed to link pore-scale processes to core-scale and field scale flow and transport. Data from such studies can be used to directly test the veracity of models for flow and transport in heterogeneous rocks, provide data for multi-stage upscaling, and reveal insights about physical/chemical processes heretofore neglected. Here we present data from three emerging techniques capable of imaging and quantifying transport properties and phenomena at the sub-core scale: magnetic resonance imaging (MRI); positron emission tomography (PET); and X-Ray CT scanning. Direct imaging of spatially resolved fluid velocities and porosity is possible with MRI (Romanenko et al., 2012). These data can be inverted to provide permeability and porosity maps at a spatial scale of ~10 cubic millimeter. PET imaging can be used to track movement of a radioactive tracer through a rock and simultaneously measure effluent tracer concentrations at a similar resolution (Boutchko et al., 2012). X-ray CT scanning of multiphase flow experiments can be used to measure capillary pressure curves and through scaling relationships, to calculate permeability at a scale of about 1 cubic millimeters(Krause et al., 2011; Pini et al., 2013). Strengths and shortcomings of these techniques are discussed--along with the benefits of combining them. Together these techniques provide a new platform from which to probe more deeply the ubiquitous influence of heterogeneity on subsurface flow and transport processes, and ultimately improve predictions of subsurface transport. Boutchk et al., 2012. Imaging and modeling of flow in porous media using clinical nuclear emission tomography systems and computational fluid dynamics. Journal of Applied geophysics, 76, 74-81. Krause, M.H., J.C. Perrin, and S.M. Benson, 2011. Modeling permeability distributions in a sandstone core for history matching core flood experiments, SPE Journal, 16, 768-777. Pini R. and Benson S., Characterization and scaling of meso-scale heterogeneities in sandstones. Geophysical Research Letters, 2013, 40. Romanenko, K., and Balscom, Permeability mapping in naturally heterogeneous sandstone cores with magnetization prepared SPRITE, 2012, 58, 3916-3926.

Colloid-Mediated Transport of Pharmaceutical and Personal Care Products through Porous Media

NASA Astrophysics Data System (ADS)

Xing, Yingna; Chen, Xijuan; Chen, Xin; Zhuang, Jie

2016-10-01

Pharmaceutical and personal care products (PPCPs) enter soils through reclaimed water irrigation and biosolid land applications. Colloids, such as clays, that are present in soil may interact with PPCPs and thus affect their fate and transport in the subsurface environment. This study addresses the influence of soil colloids on the sorption and transport behaviors of PPCPs through laboratory column experiments. Results show that the affinities of PPCPs for colloids vary with their molecular chemistry and solution ionic strength. The presence of colloids promotes the breakthrough of ciprofloxacin (over 90% sorbed on colloids) from ~4% to 30-40%, and the colloid-facilitated effect was larger at lower ionic strength (e.g., 2 mM). In comparison, the net effect of colloids on the transport of tetracycline (~50% sorbed on colloids) could be facilitation or inhibition, depending on solution chemistry. This dual effect of colloids is primarily due to the opposite response of migration of dissolved and colloid-bound tetracycline to the change in solution ionic strength. Colloids could also facilitate the transport of ibuprofen (~10% sorbed on colloids) by ~50% due likely to exclusion of dispersion pathways by colloid straining. This study suggests that colloids are significant carriers or transport promoters of some PPCPs in the subsurface environment and could affect their off-site environmental risks.

Colloid-Mediated Transport of Pharmaceutical and Personal Care Products through Porous Media

PubMed Central

Xing, Yingna; Chen, Xijuan; Chen, Xin; Zhuang, Jie

2016-01-01

Pharmaceutical and personal care products (PPCPs) enter soils through reclaimed water irrigation and biosolid land applications. Colloids, such as clays, that are present in soil may interact with PPCPs and thus affect their fate and transport in the subsurface environment. This study addresses the influence of soil colloids on the sorption and transport behaviors of PPCPs through laboratory column experiments. Results show that the affinities of PPCPs for colloids vary with their molecular chemistry and solution ionic strength. The presence of colloids promotes the breakthrough of ciprofloxacin (over 90% sorbed on colloids) from ~4% to 30–40%, and the colloid-facilitated effect was larger at lower ionic strength (e.g., 2 mM). In comparison, the net effect of colloids on the transport of tetracycline (~50% sorbed on colloids) could be facilitation or inhibition, depending on solution chemistry. This dual effect of colloids is primarily due to the opposite response of migration of dissolved and colloid-bound tetracycline to the change in solution ionic strength. Colloids could also facilitate the transport of ibuprofen (~10% sorbed on colloids) by ~50% due likely to exclusion of dispersion pathways by colloid straining. This study suggests that colloids are significant carriers or transport promoters of some PPCPs in the subsurface environment and could affect their off-site environmental risks. PMID:27734948

Preferential flow, diffuse flow, and perching in an interbedded fractured-rock unsaturated zone

NASA Astrophysics Data System (ADS)

Nimmo, John R.; Creasey, Kaitlyn M.; Perkins, Kim S.; Mirus, Benjamin B.

2017-03-01

Layers of strong geologic contrast within the unsaturated zone can control recharge and contaminant transport to underlying aquifers. Slow diffuse flow in certain geologic layers, and rapid preferential flow in others, complicates the prediction of vertical and lateral fluxes. A simple model is presented, designed to use limited geological site information to predict these critical subsurface processes in response to a sustained infiltration source. The model is developed and tested using site-specific information from the Idaho National Laboratory in the Eastern Snake River Plain (ESRP), USA, where there are natural and anthropogenic sources of high-volume infiltration from floods, spills, leaks, wastewater disposal, retention ponds, and hydrologic field experiments. The thick unsaturated zone overlying the ESRP aquifer is a good example of a sharply stratified unsaturated zone. Sedimentary interbeds are interspersed between massive and fractured basalt units. The combination of surficial sediments, basalts, and interbeds determines the water fluxes through the variably saturated subsurface. Interbeds are generally less conductive, sometimes causing perched water to collect above them. The model successfully predicts the volume and extent of perching and approximates vertical travel times during events that generate high fluxes from the land surface. These developments are applicable to sites having a thick, geologically complex unsaturated zone of substantial thickness in which preferential and diffuse flow, and perching of percolated water, are important to contaminant transport or aquifer recharge.

Preferential flow, diffuse flow, and perching in an interbedded fractured-rock unsaturated zone

USGS Publications Warehouse

Nimmo, John R.; Creasey, Kaitlyn M; Perkins, Kimberlie; Mirus, Benjamin B.

2017-01-01

Layers of strong geologic contrast within the unsaturated zone can control recharge and contaminant transport to underlying aquifers. Slow diffuse flow in certain geologic layers, and rapid preferential flow in others, complicates the prediction of vertical and lateral fluxes. A simple model is presented, designed to use limited geological site information to predict these critical subsurface processes in response to a sustained infiltration source. The model is developed and tested using site-specific information from the Idaho National Laboratory in the Eastern Snake River Plain (ESRP), USA, where there are natural and anthropogenic sources of high-volume infiltration from floods, spills, leaks, wastewater disposal, retention ponds, and hydrologic field experiments. The thick unsaturated zone overlying the ESRP aquifer is a good example of a sharply stratified unsaturated zone. Sedimentary interbeds are interspersed between massive and fractured basalt units. The combination of surficial sediments, basalts, and interbeds determines the water fluxes through the variably saturated subsurface. Interbeds are generally less conductive, sometimes causing perched water to collect above them. The model successfully predicts the volume and extent of perching and approximates vertical travel times during events that generate high fluxes from the land surface. These developments are applicable to sites having a thick, geologically complex unsaturated zone of substantial thickness in which preferential and diffuse flow, and perching of percolated water, are important to contaminant transport or aquifer recharge.

Exchange of groundwater and surface-water mediated by permafrost response to seasonal and long term air temperature variation

USGS Publications Warehouse

Ge, S.; McKenzie, J.; Voss, C.; Wu, Q.

2011-01-01

Permafrost dynamics impact hydrologic cycle processes by promoting or impeding groundwater and surface water exchange. Under seasonal and decadal air temperature variations, permafrost temperature changes control the exchanges between groundwater and surface water. A coupled heat transport and groundwater flow model, SUTRA, was modified to simulate groundwater flow and heat transport in the subsurface containing permafrost. The northern central Tibet Plateau was used as an example of model application. Modeling results show that in a yearly cycle, groundwater flow occurs in the active layer from May to October. Maximum groundwater discharge to the surface lags the maximum subsurface temperature by two months. Under an increasing air temperature scenario of 3C per 100 years, over the initial 40-year period, the active layer thickness can increase by three-fold. Annual groundwater discharge to the surface can experience a similar three-fold increase in the same period. An implication of these modeling results is that with increased warming there will be more groundwater flow in the active layer and therefore increased groundwater discharge to rivers. However, this finding only holds if sufficient upgradient water is available to replenish the increased discharge. Otherwise, there will be an overall lowering of the water table in the recharge portion of the catchment. Copyright 2011 by the American Geophysical Union.

Cometary activity and nucleus modelling: a new approach

NASA Astrophysics Data System (ADS)

Möhlmann, D.

1996-06-01

The phenomena of comet splittings with an average frequency of about one splitting per 100 years and comet (Chen and Jewitt, Icarus108, 265-271, 1994), and the restriction of cometary activity to well-defined small areas at the almost passive and mantle covered surface (Keller et al., ESA SP-250, Vol. II, pp. 363-364, 1986) are at present driving challenges to models of structure and evolution of comet nuclei. Extending the presently discussed models by incorporating lateral subsurface transport of sublimed volatiles, there appears the possibility that the places of sublimation are different from those of activity (the so-called active areas). Then, there is no necessity to distinguish between different surface properties at active and passive areas, assuming, e.g. an uncovered icy surface at active areas. Active areas are simply the very local "source sites" where the accumulated subsurface flows from distant regions reach the surface. The pressure driven subsurface flows of volatiles may not only leave the comet at its surface, they may penetrate via cracks, etc. also deeply into the nucleus. There they can cause a further growth of cracks and also new cracks. This can be a cause for the observed regular splittings. Furthermore, actual models (Kührt and Keller, Icarus109, 121-132, 1994; Skorov and Rickman, Planet. Space Sci.43, 1587-1594, 1995) of the gas transport through porous comet surface crusts can be interpreted as to give first indications for thermodynamical parameters in heat conducting and porous cometary crusts which are appropriate for 1 AU conditions to permit the temporary existence of a layer with fluid subsurface water within these crusts. This exciting result of the possible temporary existence of subsurface warm water in comets which approach the Sun within about 1 AU makes a cometary subsurface chemistry much more efficient than expected hitherto.

Study of the Martian Subsurface with a Fiber Optics Spectrometer: the Ma_Miss Experiment

NASA Astrophysics Data System (ADS)

Coradini, A.; de Sanctis, M. C.; Ammannito, E.; Boccaccini, A.; Battistelli, E.; Capanni, A.

2009-04-01

In this presentation is described the investigation that we intend to do with a small imaging spectrometer that will be inserted in the drill of the Exomars- Pasteur rover. This spectrometer is named Ma_miss (Mars Multispectral Imager for Subsurface Studies ). The Ma_Miss experiment is located in the drill ,that will be able to make a hole in the Mars soil and rock up to 2 m. Ma_Miss includes the optical head of the spectrometer, a lamp to illuminate the borehole walls, and the optical fiber that brings the signal to the spectrometer. The multispectral images are acquired by means of a sapphire window placed on the lateral wall of the drill tool, as close as possible to the drill head. The images are gathered by means of an optical fibre system and analyzed using the spectrometer. The Ma_Miss gathered light containing the scientific information is transferred to the array detector and electronics of the instrument by means of an optical rotary joint implemented in the roto-translation group of the drill, as shown in the next pictures In the figure is schematically represented the Ma_Miss- Dibs architecture. This experiment will be extremely valuable since it will allow, for the first time, to have an idea of the mineralogical composition of the Martian subsurface and to study freshly cut rocks. The study of surface and subsurface mineralogy of Martian soil and rocks is the key for understanding the chemico-physical processes that led to the formation and evolution of the Red Planet. The history of the water and other volatiles, as well as the signatures of weathering processes are important to understand present and past environmental conditions associated with the possibility of life. Surface samples are highly influenced by exogenous processes (weathering, erosion, sedimentation, impact) that alter their original properties. So, the analyses of uncontaminated samples by means of instrumented drills and in situ analytic stations are the key for unambiguous interpretation of the original environment that leading to the formation of rocks. Analysis of subsurface layers is the only approach that warranties measurements on samples close to their original composition. The upper few meters of the surface materials on Mars play a crucial role in its history, providing important constraints geologic, hydrologic, and climatic to the history of the planet. Drilling into the near-surface crust will provide an opportunity to assess variations in composition, texture, stratification, unconformities, etc. that will help define its lithology and structure, and provide important clues regarding its origin and subsequent evolution. The subsurface material can give information on the evolution of surface sediments (erosion, transport, deposition), on the relation between sediments and bedrock, on the relation between environmental conditions and surface processes permitting to "investigate planetary processes that influence habitability." Investigation of mineralogical composition of near-surface geological materials is needed to fully characterize the geology of the regions that will be visited by the Rover at all appropriate spatial scales, and to interpret the processes that have formed and modified rocks and regolith. Subsurface access, sampling material below the oxidized layer, can be the key to "assess the biological potential of the target environment (past or present)". To date, we have direct observations relative only to the Martian surface. Little is known about the characteristics of the first subsurface layers. The possibility to sample subsurface materials to be delivered to other instruments, and to record the context of the sampled soil doing in situ borehole mineralogical analysis, is fundamental to search for traces of past or present life on Mars. The spectrometer observes a single point target, having 0.1 mm diameter, on the borehole wall surface. Depending on the surface features we are interested in, the observation window can scan the borehole's surface by means of drill tip rotation or translation. When the drill is translated, a "Column Image" is acquired. This translation step can be equal to the observation spot (0.1 mm). The "Ring Image" can be obtained by rotation of the drill tip; a rotation step of about 0.5˚ (corresponding to 720 acquisitions in the ring) is sufficient to assure the full coverage of the ring.

Using geothermal energy to heat a portion of a formation for an in situ heat treatment process

DOEpatents

Pieterson, Roelof; Boyles, Joseph Michael; Diebold, Peter Ulrich

2010-06-08

Methods of using geothermal energy to treat subsurface formations are described herein. Methods for using geothermal energy to treat a subsurface treatment area containing or proximate to hydrocarbons may include producing geothermally heated fluid from at least one subsurface region. Heat from at least a portion of the geothermally heated fluid may be transferred to the subsurface treatment area to heat the subsurface treatment area. At least some hydrocarbon fluids may be produced from the formation.

Gypsies in the palace: Experimentalist's view on the use of 3-D physics-based simulation of hillslope hydrological response

USGS Publications Warehouse

James, A.L.; McDonnell, Jeffery J.; Tromp-Van Meerveld, I.; Peters, N.E.

2010-01-01

As a fundamental unit of the landscape, hillslopes are studied for their retention and release of water and nutrients across a wide range of ecosystems. The understanding of these near-surface processes is relevant to issues of runoff generation, groundwater-surface water interactions, catchment export of nutrients, dissolved organic carbon, contaminants (e.g. mercury) and ultimately surface water health. We develop a 3-D physics-based representation of the Panola Mountain Research Watershed experimental hillslope using the TOUGH2 sub-surface flow and transport simulator. A recent investigation of sub-surface flow within this experimental hillslope has generated important knowledge of threshold rainfall-runoff response and its relation to patterns of transient water table development. This work has identified components of the 3-D sub-surface, such as bedrock topography, that contribute to changing connectivity in saturated zones and the generation of sub-surface stormflow. Here, we test the ability of a 3-D hillslope model (both calibrated and uncalibrated) to simulate forested hillslope rainfall-runoff response and internal transient sub-surface stormflow dynamics. We also provide a transparent illustration of physics-based model development, issues of parameterization, examples of model rejection and usefulness of data types (e.g. runoff, mean soil moisture and transient water table depth) to the model enterprise. Our simulations show the inability of an uncalibrated model based on laboratory and field characterization of soil properties and topography to successfully simulate the integrated hydrological response or the distributed water table within the soil profile. Although not an uncommon result, the failure of the field-based characterized model to represent system behaviour is an important challenge that continues to vex scientists at many scales. We focus our attention particularly on examining the influence of bedrock permeability, soil anisotropy and drainable porosity on the development of patterns of transient groundwater and sub-surface flow. Internal dynamics of transient water table development prove to be essential in determining appropriate model parameterization. ?? 2010 John Wiley & Sons, Ltd.

PFLOTRAN: Reactive Flow & Transport Code for Use on Laptops to Leadership-Class Supercomputers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hammond, Glenn E.; Lichtner, Peter C.; Lu, Chuan

PFLOTRAN, a next-generation reactive flow and transport code for modeling subsurface processes, has been designed from the ground up to run efficiently on machines ranging from leadership-class supercomputers to laptops. Based on an object-oriented design, the code is easily extensible to incorporate additional processes. It can interface seamlessly with Fortran 9X, C and C++ codes. Domain decomposition parallelism is employed, with the PETSc parallel framework used to manage parallel solvers, data structures and communication. Features of the code include a modular input file, implementation of high-performance I/O using parallel HDF5, ability to perform multiple realization simulations with multiple processors permore » realization in a seamless manner, and multiple modes for multiphase flow and multicomponent geochemical transport. Chemical reactions currently implemented in the code include homogeneous aqueous complexing reactions and heterogeneous mineral precipitation/dissolution, ion exchange, surface complexation and a multirate kinetic sorption model. PFLOTRAN has demonstrated petascale performance using 2{sup 17} processor cores with over 2 billion degrees of freedom. Accomplishments achieved to date include applications to the Hanford 300 Area and modeling CO{sub 2} sequestration in deep geologic formations.« less

Carbon Characteristics and Biogeochemical Processes of Uranium Accumulating Organic Matter Rich Sediments in the Upper Colorado River Basin

NASA Astrophysics Data System (ADS)

Boye, K.; Noel, V.; Tfaily, M. M.; Dam, W. L.; Bargar, J.; Fendorf, S. E.

2015-12-01

Uranium plume persistence in groundwater aquifers is a problem on several former ore processing sites on floodplains in the upper Colorado River Basin. Earlier observations by our group and others at the Old Rifle Site, CO, have noted that U concentrations are highest in organic rich, fine-grained, and, therefore, diffusion limited sediment material. Due to the constantly evolving depositional environments of floodplains, surficial organic matter may become buried at various stages of decomposition, through sudden events such as overbank flooding and through the slower progression of river meandering. This creates a discontinuous subsurface distribution of organic-rich sediments, which are hotspots for microbial activity and thereby central to the subsurface cycling of contaminants (e.g. U) and biologically relevant elements (e.g. C, N, P, Fe). However, the organic matter itself is poorly characterized. Consequently, little is known about its relevance in driving biogeochemical processes that control U fate and transport in the subsurface. In an investigation of soil/sediment cores from five former uranium ore processing sites on floodplains distributed across the Upper Colorado River Basin we confirmed consistent co-enrichment of U with organic-rich layers in all profiles. However, using C K-edge X-ray Absorption Spectroscopy (XAS) coupled with Fourier-Transformed Ion-Cyclotron-Resonance Mass-Spectroscopy (FT-ICR-MS) on bulk sediments and density-separated organic matter fractions, we did not detect any chemical difference in the organic rich sediments compared to the surrounding coarser-grained aquifer material within the same profile, even though there were differences in organic matter composition between the 5 sites. This suggests that U retention and reduction to U(IV) is independent of C chemical composition on the bulk scale. Instead it appears to be the abundance of organic matter in combination with a limited O2 supply in the fine-grained material that stimulate anaerobic microbial processes responsible for U enrichment. Thus, the chemical composition of organic matter is subordinate to the physical environment and total organic matter content in controlling U reduction and retention processes.

Biodegradation of PuEDTA and Impacts on Pu Mobility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xun, Luying; Bolton, Jr., Harvey

Ethylenediaminetetraacetate (EDTA) and nitrilotriacetate (NTA) are synthetic chelating agents, which can form strong water-soluble complexes with radionuclides and metals and has been used to decontaminate and process nuclear materials. Synthetic chelating agents were co-disposed with radionuclides (e.g., 60Co, Pu) and heavy metals enhancing their transport in the subsurface. An understanding of EDTA biodegradation is essential to help mitigate enhanced radionuclide transport by EDTA. The objective of this research is to develop fundamental data on factors that govern the biodegradation of radionuclide-EDTA. These factors include the dominant EDTA aqueous species, the biodegradation of various metal-EDTA complexes, the uptake of various metal-EDTAmore » complexes into the cell, the distribution and mobility of the radionuclide during and after EDTA biodegradation, and the enzymology and genetics of EDTA biodegradation.« less

Mathematical Modelling of Bacterial Populations in Bio-remediation Processes

NASA Astrophysics Data System (ADS)

Vasiliadou, Ioanna A.; Vayenas, Dimitris V.; Chrysikopoulos, Constantinos V.

2011-09-01

An understanding of bacterial behaviour concerns many field applications, such as the enhancement of water, wastewater and subsurface bio-remediation, the prevention of environmental pollution and the protection of human health. Numerous microorganisms have been identified to be able to degrade chemical pollutants, thus, a variety of bacteria are known that can be used in bio-remediation processes. In this study the development of mathematical models capable of describing bacterial behaviour considered in bio-augmentation plans, such as bacterial growth, consumption of nutrients, removal of pollutants, bacterial transport and attachment in porous media, is presented. The mathematical models may be used as a guide in designing and assessing the conditions under which areas contaminated with pollutants can be better remediated.

Surface and subsurface cracks characteristics of single crystal SiC wafer in surface machining

NASA Astrophysics Data System (ADS)

Qiusheng, Y.; Senkai, C.; Jisheng, P.

2015-03-01

Different machining processes were used in the single crystal SiC wafer machining. SEM was used to observe the surface morphology and a cross-sectional cleavages microscopy method was used for subsurface cracks detection. Surface and subsurface cracks characteristics of single crystal SiC wafer in abrasive machining were analysed. The results show that the surface and subsurface cracks system of single crystal SiC wafer in abrasive machining including radial crack, lateral crack and the median crack. In lapping process, material removal is dominated by brittle removal. Lots of chipping pits were found on the lapping surface. With the particle size becomes smaller, the surface roughness and subsurface crack depth decreases. When the particle size was changed to 1.5µm, the surface roughness Ra was reduced to 24.0nm and the maximum subsurface crack was 1.2µm. The efficiency of grinding is higher than lapping. Plastic removal can be achieved by changing the process parameters. Material removal was mostly in brittle fracture when grinding with 325# diamond wheel. Plow scratches and chipping pits were found on the ground surface. The surface roughness Ra was 17.7nm and maximum subsurface crack depth was 5.8 µm. When grinding with 8000# diamond wheel, the material removal was in plastic flow. Plastic scratches were found on the surface. A smooth surface of roughness Ra 2.5nm without any subsurface cracks was obtained. Atomic scale removal was possible in cluster magnetorheological finishing with diamond abrasive size of 0.5 µm. A super smooth surface eventually obtained with a roughness of Ra 0.4nm without any subsurface crack.

Hydrocarbon lakes on Titan: Distribution and interaction with a porous regolith

USGS Publications Warehouse

Hayes, A.; Aharonson, O.; Callahan, P.; Elachi, C.; Gim, Y.; Kirk, R.; Lewis, K.; Lopes, R.; Lorenz, R.; Lunine, J.; Mitchell, Ken; Mitri, Giuseppe; Stofan, E.; Wall, S.

2008-01-01

Synthetic Aperture Radar (SAR) images of Titan's north polar region reveal quasi-circular to complex features which are interpreted to be liquid hydrocarbon lakes. We investigate methane transport in Titan's hydrologic cycle using the global distribution of lake features. As of May 2007, the SAR data set covers ???22% of the surface and indicates multiple lake morphologies which are correlated across the polar region. Lakes are limited to latitudes above 55??N and vary from <10 to more than 100,000 km2. The size and location of lakes provide constraints on parameters associated with subsurface transport. Using porous media properties inferred from Huygens probe observations, timescales for flow into and out of observed lakes are shown to be in the tens of years, similar to seasonal cycles. Derived timescales are compared to the time between collocated SAR observations in order to consider the role of subsurface transport in Titan's hydrologic cycle. Copyright 2008 by the American Geophysical Union.

Effect of synthetic iron colloids on the microbiological NH(4)(+) removal process during groundwater purification.

PubMed

Wolthoorn, Anke; Temminghoff, Erwin J M; van Riemsdijk, Willem H

2004-04-01

Subsurface aeration is used to oxidise Fe in situ in groundwater that is used to make drinking water potable. In a groundwater system with pH>7 subsurface aeration results in non-mobile Fe precipitate and mobile Fe colloids. Since originally the goal of subsurface aeration is to remove iron in situ, the formation of non-mobile iron precipitate, which facilitates the metal's removal, is the desired result. In addition to this intended effect, subsurface aeration may also strongly enhance the microbiological removal of ammonium (NH(4)(+)) in the purification station. Mobile iron colloids could be the link between subsurface aeration and the positive effect on the NH(4)(+) removal process. Therefore, the objective of this study was to assess whether synthetic iron colloids could improve the NH(4)(+) removal process. The effect of synthetic iron colloids on the NH(4)(+) removal process was studied using an artificial purification set-up on a laboratory scale. Columns that purified groundwater with or without added synthetic iron colloids were set up in duplicate. The results showed that the NH(4)(+) removal was significantly ( alpha = 0.05 ) increased in columns treated with the synthetic iron colloids. Cumulative after 4 months about 10% more NH(4)(+) was nitrified in the columns that was treated with the groundwater containing synthetic iron colloids. The results support the hypothesis that mobile iron colloids could be the link between subsurface aeration and the positive effect on the NH(4)(+) removal process.

Blueprint for a coupled model of sedimentology, hydrology, and hydrogeology in streambeds

NASA Astrophysics Data System (ADS)

Partington, Daniel; Therrien, Rene; Simmons, Craig T.; Brunner, Philip

2017-06-01

The streambed constitutes the physical interface between the surface and the subsurface of a stream. Across all spatial scales, the physical properties of the streambed control surface water-groundwater interactions. Continuous alteration of streambed properties such as topography or hydraulic conductivity occurs through erosion and sedimentation processes. Recent studies from the fields of ecology, hydrogeology, and sedimentology provide field evidence that sedimentological processes themselves can be heavily influenced by surface water-groundwater interactions, giving rise to complex feedback mechanisms between sedimentology, hydrology, and hydrogeology. More explicitly, surface water-groundwater exchanges play a significant role in the deposition of fine sediments, which in turn modify the hydraulic properties of the streambed. We explore these feedback mechanisms and critically review the extent of current interaction between the different disciplines. We identify opportunities to improve current modeling practices. For example, hydrogeological models treat the streambed as a static rather than a dynamic entity, while sedimentological models do not account for critical catchment processes such as surface water-groundwater exchange. We propose a blueprint for a new modeling framework that bridges the conceptual gaps between sedimentology, hydrogeology, and hydrology. Specifically, this blueprint (1) fully integrates surface-subsurface flows with erosion, transport, and deposition of sediments and (2) accounts for the dynamic changes in surface elevation and hydraulic conductivity of the streambed. Finally, we discuss the opportunities for new research within the coupled framework.

Impact of topography on groundwater salinization due to ocean surge inundation

NASA Astrophysics Data System (ADS)

Yu, Xuan; Yang, Jie; Graf, Thomas; Koneshloo, Mohammad; O'Neal, Michael A.; Michael, Holly A.

2016-08-01

Sea-level rise and increases in the frequency and intensity of ocean surges caused by climate change are likely to exacerbate adverse effects on low-lying coastal areas. The landward flow of water during ocean surges introduces salt to surficial coastal aquifers and threatens groundwater resources. Coastal topographic features (e.g., ponds, dunes, barrier islands, and channels) likely have a strong impact on overwash and salinization processes, but are generally highly simplified in modeling studies. To understand topographic impacts on groundwater salinization, we modeled a theoretical overwash event and variable-density groundwater flow and salt transport in 3-D using the fully coupled surface and subsurface numerical simulator, HydroGeoSphere. The model simulates the coastal aquifer as an integrated system considering overland flow, coupled surface and subsurface exchange, variably saturated flow, and variable-density groundwater flow. To represent various coastal landscape types, we simulated both synthetic fields and real-world coastal topography from Delaware, USA. The groundwater salinization assessment suggested that the topographic connectivity promoting overland flow controls the volume of aquifer that is salinized. In contrast, the amount of water that can be stored in surface depressions determines the amount of seawater that infiltrates the subsurface and the time for seawater to flush from the aquifer. Our study suggests that topography has a significant impact on groundwater salinization due to ocean surge overwash, with important implications for coastal land management and groundwater vulnerability assessment.

Biofiltration of Volatile Pollutants: Solubility Effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davison, Brian H.; Barton, John W.

2001-06-15

This project investigates and collects fundamental partitioning data for a variety of sparingly soluble subsurface contaminants (e.g., TCE, etc.) between vapor, aqueous phase, and matrices containing substantial quantities of biomass and biomass components. Due to the difficulty of obtaining these measurements, environmental models have generally used solubility constants of chemicals in pure water or, in a few rare cases, simple linear models. Our prior EMSP work has shown that the presence of biological material can increase effective solubilities by an order of magnitude for sparingly soluble organics; therefore, the previous simple approaches are not valid and are extremely poor predictorsmore » of actual bio-influenced partitioning. It is likely that environmental contaminants will partition in a similar manner into high-biomass phases (e.g. biobarriers and plants) or humic soils. Biological material in the subsurface can include lipids, fatty acids, humic materials, as well a s the lumped and difficult to estimate 'biomass'. Our measurements include partition into these biological materials to allow better estimation. Fundamental data collected will be used in mathematical models predicting transport and sorption in subsurface environments, with the impacts on bioremediation being evaluated based on this new information. Our 2-D Win95/98 software program, Biofilter 1.0, developed as a part of our prior EMSP efforts for describing biofiltration processes with consideration given to both kinetic and mass transfer factors, will be extended to incorporate and use this information.« less

Biofiltration of Volatile Pollutants: Solubility Effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davison, Brian H.; Barton, John W.

2002-06-15

This project investigates and collects fundamental partitioning data for a variety of sparingly soluble subsurface contaminants (e.g., TCE, etc.) between vapor, aqueous phase, and matrices containing substantial quantities of biomass and biomass components. Due to the difficulty of obtaining these measurements, environmental models have generally used solubility constants of chemicals in pure water or, in a few rare cases, simple linear models. Our prior EMSP work has shown that the presence of biological material can increase effective solubilities by an order of magnitude for sparingly soluble organics; therefore, the previous simple approaches are not valid and are extremely poor predictorsmore » of actual bio-influenced partitioning. It is likely that environmental contaminants will partition in a similar manner into high-biomass phases (e.g. biobarriers and plants) or humic soils. Biological material in the subsurface can include lipids, fatty acids, humic materials, as well as the lumped and difficult-to-estimate 'biomass'. Our measurements include partition into these biological materials to allow better estimation. Fundamental data collected will be used in mathematical models predicting transport and sorption in subsurface environments, with the impacts on bioremediation being evaluated based on this new information. Our 2-D Win95/98/XP software program, Biofilter 1.0, developed as a part of our prior EMSP efforts for describing biofiltration processes with consideration given to both kinetic and mass transfer factors, is being extended to incorporate and use this information.« less

Comparison of point-source pollutant loadings to soil and groundwater for 72 chemical substances.

PubMed

Yu, Soonyoung; Hwang, Sang-Il; Yun, Seong-Taek; Chae, Gitak; Lee, Dongsu; Kim, Ki-Eun

2017-11-01

Fate and transport of 72 chemicals in soil and groundwater were assessed by using a multiphase compositional model (CompFlow Bio) because some of the chemicals are non-aqueous phase liquids or solids in the original form. One metric ton of chemicals were assumed to leak in a stylized facility. Scenarios of both surface spills and subsurface leaks were considered. Simulation results showed that the fate and transport of chemicals above the water table affected the fate and transport of chemicals below the water table, and vice versa. Surface spill scenarios caused much less concentrations than subsurface leak scenarios because leaching amounts into the subsurface environment were small (at most 6% of the 1 t spill for methylamine). Then, simulation results were applied to assess point-source pollutant loadings to soil and groundwater above and below the water table, respectively, by multiplying concentrations, impact areas, and durations. These three components correspond to the intensity of contamination, mobility, and persistency in the assessment of pollutant loading, respectively. Assessment results showed that the pollutant loadings in soil and groundwater were linearly related (r 2  = 0.64). The pollutant loadings were negatively related with zero-order and first-order decay rates in both soil (r = - 0.5 and - 0.6, respectively) and groundwater (- 1.0 and - 0.8, respectively). In addition, this study scientifically defended that the soil partitioning coefficient (K d ) significantly affected the pollutant loadings in soil (r = 0.6) and the maximum masses in groundwater (r = - 0.9). However, K d was not a representative factor for chemical transportability unlike the expectation in chemical ranking systems of soil and groundwater pollutants. The pollutant loadings estimated using a physics-based hydrogeological model provided a more rational ranking for exposure assessment, compared to the summation of persistency and transportability scores in the chemical ranking systems. In the surface spill scenario, the pollutant loadings were zeros for all chemicals, except methylamine to soil whose pollutant loading was smaller than that in the subsurface leak scenario by 4 orders of magnitude. The maximum mass and the average mass multiplied by duration in soil greatly depended on leaching fluxes (r = 1.0 and 0.9, respectively), while the effect of leaching fluxes diminished below the water table. The contribution of this work is that a physics-based numerical model was used to quantitatively compare the subsurface pollutant loading in a chemical accident for 72 chemical substances, which can scientifically defend a simpler and more qualitative assessment of pollutant loadings. Besides, this study assessed pollutant loadings to soil (unsaturated zone) and groundwater (saturated zone) all together and discussed their interactions.

Groundwater in geologic processes, 2nd edition

USGS Publications Warehouse

Ingebritsen, Steven E.; Sanford, Ward E.; Neuzil, Christopher E.

2006-01-01

Interest in the role of Groundwater in Geologic Processes has increased steadily over the past few decades. Hydrogeologists and geologists are now actively exploring the role of groundwater and other subsurface fluids in such fundamental geologic processes as crustal heat transfer, ore deposition, hydrocarbon migration, earthquakes, tectonic deformation, diagenesis, and metamorphism.Groundwater in Geologic Processes is the first comprehensive treatment of this body of inquiry. Chapters 1 to 4 develop the basic theories of groundwater motion, hydromechanics, solute transport, and heat transport. Chapter 5 applies these theories to regional groundwater flow systems in a generic sense, and Chapters 6 to 13 focus on particular geologic processes and environments. Relative to the first edition of Groundwater in Geologic Processes , this second edition includes a much more comprehensive treatment of hydromechanics (the coupling of groundwater flow and deformation). It also includes new chapters on "compaction and diagenesis," "metamorphism," and "subsea hydrogeology." Finally, it takes advantage of the substantial body of published research that has appeared since the first edition in 1998. The systematic presentation of theory and application, and the problem sets that conclude each chapter, make this book ideal for undergraduate- and graduate-level geology courses (assuming that the students have some background in calculus and introductory chemistry). It also serves as an invaluable reference for researchers and other professionals in the field

Pathogen transport in groundwater systems: Contrasts with traditional solute transport

USGS Publications Warehouse

Hunt, Randall J.; Johnson, William P.

2017-01-01

Water quality affects many aspects of water availability, from precluding use to societal perceptions of fit-for-purpose. Pathogen source and transport processes are drivers of water quality because they have been responsible for numerous outbreaks resulting in large economic losses due to illness and, in some cases, loss of life. Outbreaks result from very small exposure (e.g., less than 20 viruses) from very strong sources (e.g., trillions of viruses shed by a single infected individual). Thus, unlike solute contaminants, an acute exposure to a very small amount of contaminated water can cause immediate adverse health effects. Similarly, pathogens are larger than solutes. Thus, interactions with surfaces and settling become important even as processes important for solutes such as diffusion become less important. These differences are articulated in “Colloid Filtration Theory”, a separate branch of pore-scale transport. Consequently, understanding pathogen processes requires changes in how groundwater systems are typically characterized, where the focus is on the leading edges of plumes and preferential flow paths, even if such features move only a very small fraction of the aquifer flow. Moreover, the relatively short survival times of pathogens in the subsurface require greater attention to very fast (<10 year) flow paths. By better understanding the differences between pathogen and solute transport mechanisms discussed here, a more encompassing view of water quality and source water protection is attained. With this more holistic view and theoretical understanding, better evaluations can be made regarding drinking water vulnerability and the relation between groundwater and human health.

Adapting HYDRUS-1D to simulate overland flow and reactive transport during sheet flow deviations

USDA-ARS?s Scientific Manuscript database

The HYDRUS-1D code is a popular numerical model for solving the Richards equation for variably-saturated water flow and solute transport in porous media. This code was adapted to solve rather than the Richards equation for subsurface flow the diffusion wave equation for overland flow at the soil sur...

Studies Based on Lunar Global Subsurface Radar Sounding Data Obtained by SELENE (Kaguya)

NASA Astrophysics Data System (ADS)

Kumamoto, A.; Yamaguchi, Y.; Yamaji, A.; Oshigami, S.; Ishiyama, K.; Nakamura, N.; Haruyama, J.; Miyamoto, H.; Nishibori, T.; Tsuchiya, F.; Ohtake, M.

2018-04-01

Several studies based on lunar global subsurface radar sounding data obtained by SELENE/LRS will be reviewed. From the subsurface structures of the buried regolith layers, we can discuss the evolution of tectonic and volcanic processes in the maria.

Deep and Ultra-deep Underground Observatory for In Situ Stress, Fluids, and Life

NASA Astrophysics Data System (ADS)

Boutt, D. F.; Wang, H.; Kieft, T. L.

2008-12-01

The question 'How deeply does life extend into the Earth?' forms a single, compelling vision for multidisciplinary science opportunities associated with physical and biological processes occurring naturally or in response to construction in the deep and ultra-deep subsurface environment of the Deep Underground Science and Engineering Laboratory (DUSEL) in the former Homestake mine. The scientific opportunity is to understand the interaction between the physical environment and microbial life, specifically, the coupling among (1) stress state and deformation; (2) flow and transport and origin of fluids; and (3) energy and nutrient sources for microbial life; and (4) microbial identity, diversity and activities. DUSEL-Homestake offers the environment in which these questions can be addressed unencumbered by competing human activities. Associated with the interaction among these variables are a number of questions that will be addressed at variety of depths and scales in the facility: What factors control the distribution of life as a function of depth and temperature? What patterns in microbial diversity, microbial activity and nutrients are found along this gradient? How do state variables (stress, strain, temperature, and pore pressure) and constitutive properties (permeability, porosity, modulus, etc.) vary with scale (space, depth, time) in a large 4D heterogeneous system: core - borehole - drift - whole mine - regional? How are fluid flow and stress coupled in a low-permeability, crystalline environment dominated by preferential flow paths? How does this interaction influence the distribution of fluids, solutes, gases, colloids, and biological resources (e.g. energy and nutritive substrates) in the deep continental subsurface? What is the interaction between geomechanics/geohydrology and microbiology (microbial abundance, diversity, distribution, and activities)? Can relationships elucidated within the mechanically and hydrologically altered subsurface habitat of the Homestake DUSEL be extrapolated to the pristine subsurface biosphere? In the absence of extensive intrusive investigations (drifts, mines, etc), can we characterize hydrogeologic and geomechanical processes in the subsurface? To what depth can we effectively characterize such processes, and what is the confidence in our interpretations? In addition to addressing these question in the 10-km3 of mine volume, the Homestake facility offers the deepest drilling platform in North America. The extant depth of 8000 feet can be doubled by drilling. An array of three or more 8,200 ft. boreholes, wire-line drilled from the 8,000 ft. level at Homestake will probe to at least 16,200 ft. below land surface, a depth at this location approaching the expected lower biosphere limit (e.g. the 120°C isotherm). Cores will be collected aseptically and then fracture patterns (e.g., orientation, aperture, etc.) will be determined and fracture fluids will be intensively sampled over time. Cores and fracture fluids will be analyzed for indigenous microbial communities, including their genetic elements, metabolic processes, and biosignatures.

Recent Advances in the Area of Groundwater

NASA Astrophysics Data System (ADS)

Bahr, J. M.

2017-12-01

Groundwater related papers published in Water Resources Research in the last year range from experimental and modeling studies of pore scale flow and reactive transport to assessments of changes in water storage at the scale of regional aquifers enabled by satellite observations. Important societal needs motivating these studies include sustainability of groundwater resources of suitable quantity and quality for human use, protection of groundwater-dependent ecosystems in streams, wetlands, lakes and coastal areas, and assessment of the feasibility of subsurface sequestration of carbon dioxide and long-lived radioactive wastes. Eight general areas that generated ten or more papers within the period July 2016 to June 2017 are the following: aquifer heterogeneity (including geostatistical and inverse methods for parameter estimation), flow and transport in the unsaturated zone (including recharge to and evaporative losses from aquifers), multiphase flow and transport (including processes relevant to carbon sequestration), groundwater-surface water interactions (particularly hyporheic exchange), flow and transport in fractured media, novel remote sensing and geophysical techniques for aquifer characterization and assessment of groundwater dynamics, freshwater-saltwater interactions (particularly in coastal aquifers), and reactive solute transport. This presentation will highlight selected findings in each of these areas.

In-situ Subsurface Soil Analyzer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulmer, Chris

The Department of Energy’s (DOE’s) Terrestrial Ecosystem Science (TES) program is seeking improved sensor systems for monitoring hydro-biogeochemical processes in complex subsurface environments. The TES program is specifically interested in acquiring chemical and structural information regarding the type and nature of the hydration and redox states of subsurface chemical species. The technology should be able to perform on-site and real-time measurements to provide information not available using current sample acquisition and preservation processes. To address the needs of the DOE and the terrestrial science community, Physical Optics Corporation (POC) worked on the development of a new In-Situ Subsurface Soil Analyzermore » (ISSA) based on magnetic resonance technologies. Benchtop testing was performed to assess the feasibility of continuous wave electron pair resonance (CW-EPR) detection of chemical species in subsurface soil systems.« less

Laboratory studies of the diagenesis and mobility of 239,240pu and 137Cs in nearshore sediments

NASA Astrophysics Data System (ADS)

Sholkovitz, Edward R.; Cochran, J. Kirk; Carey, Anne E.

1983-08-01

Controlled laboratory experiments have been used to study the diagenetic chemistry of 239,240Pu 137Cs, and 55Fe. Experiments using Buzzards Bay sediments in small tanks show that sulfate reduction is accompanied by the production of large pore water concentration gradients of alkalinity, phosphate, ammonia and dissolved organic carbon and the formation of subsurface maxima in Fe and Mn. These pore water profiles demonstrate that bacterially-mediated processes of organic matter degradation and redox reactions can be simulated in the laboratory. A vertical profile of 55Fe in pore waters is reported for the first time: it follows the profile of stable Fe and as such has a large (200 dpm/100 kg) subsurface maximum between 2-4 cm depth. Comparison of 55Fe/Fe ratios in sediments and pore waters shows that there is preferential solubilization of 55Fe over stable Fe. The pore water activities of 239,240Pu show no gradients within the large uncertainties of the counting statistics, but are two to four times higher than Buzzards Bay seawater (0.05 dpm/100 kg). The activity of 137Cs in the pore water profile is constant (40 dpm/100 kg) within the large counting uncertainties and is twice that of Buzzards Bay seawater. Cs-137 does not appear to be involved in diagenetic chemistry but may increase in pore waters as a result of ion exchange reactions. Flux estimates based on the pore water data show that remobilization and transport of 239,240 Pu in coastal sediments are not significant processes while the transport of l37Cs may be.

Regolith-atmosphere exchange of water in Mars' recent past

NASA Astrophysics Data System (ADS)

Steele, Liam J.; Balme, Matthew R.; Lewis, Stephen R.

2017-03-01

We investigate the exchange of water vapour between the regolith and atmosphere of Mars, and how it varies with different orbital parameters, atmospheric dust contents and surface water ice reservoirs. This is achieved through the coupling of a global circulation model (GCM) and a regolith diffusion model. GCM simulations are performed for hundreds of Mars years, with additional one-dimensional simulations performed for 50 kyr. At obliquities ɛ =15∘ and 30°, the thermal inertia and albedo of the regolith have more control on the subsurface water distribution than changes to the eccentricity or solar longitude of perihelion. At ɛ =45∘ , atmospheric water vapour abundances become much larger, allowing stable subsurface ice to form in the tropics and mid-latitudes. The circulation of the atmosphere is important in producing the subsurface water distribution, with increased water content in various locations due to vapour transport by topographically-steered flows and stationary waves. As these circulation patterns are due to topographic features, it is likely the same regions will also experience locally large amounts of subsurface water at different epochs. The dustiness of the atmosphere plays an important role in the distribution of subsurface water, with a dusty atmosphere resulting in a wetter water cycle and increased stability of subsurface ice deposits.

Using Multiscale Modeling to Study Coupled Flow, Transport, Reaction and Biofilm Growth Processes in Porous Media

NASA Astrophysics Data System (ADS)

Valocchi, A. J.; Laleian, A.; Werth, C. J.

2017-12-01

Perturbation of natural subsurface systems by fluid inputs may induce geochemical or microbiological reactions that change porosity and permeability, leading to complex coupled feedbacks between reaction and transport processes. Some examples are precipitation/dissolution processes associated with carbon capture and storage and biofilm growth associated with contaminant transport and remediation. We study biofilm growth due to mixing controlled reaction of multiple substrates. As biofilms grow, pore clogging occurs which alters pore-scale flow paths thus changing the mixing and reaction. These interactions are challenging to quantify using conventional continuum-scale porosity-permeability relations. Pore-scale models can accurately resolve coupled reaction, biofilm growth and transport processes, but modeling at this scale is not feasible for practical applications. There are two approaches to address this challenge. Results from pore-scale models in generic pore structures can be used to develop empirical relations between porosity and continuum-scale parameters, such as permeability and dispersion coefficients. The other approach is to develop a multiscale model of biofilm growth in which non-overlapping regions at pore and continuum spatial scales are coupled by a suitable method that ensures continuity of flux across the interface. Thus, regions of high reactivity where flow alteration occurs are resolved at the pore scale for accuracy while regions of low reactivity are resolved at the continuum scale for efficiency. This approach thus avoids the need for empirical upscaling relations in regions with strong feedbacks between reaction and porosity change. We explore and compare these approaches for several two-dimensional cases.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyd, P.W.; Gall, M.P.; Silver, M.W.

A central question addressed by the VERTIGO (VERtical Transport In the Global Ocean) study was 'What controls the efficiency of particle export between the surface and subsurface ocean'? Here, we present data from sites at ALOHA (N Central Pacific Gyre) and K2 (NW subarctic Pacific) on phytoplankton processes, and relate them via a simple planktonic foodweb model, to subsurface particle export (150-500 m). Three key factors enable quantification of the surface-subsurface coupling: a sampling design to overcome the temporal lag and spatial displacement between surface and subsurface processes; data on the size-partitioning of Net Primary Production (NPP) and subsequent transformationsmore » prior to export; estimates of the ratio of algal- to faecal-mediated vertical export flux. At ALOHA, phytoplankton were characterized by low stocks, NPP, F{sub v}/F{sub m} (N-limited), and were dominated by picoplankton. The HNLC waters at K2 were characterized by both two-fold changes in NPP and floristic shifts (high to low proportion of diatoms) between deployment 1 and 2. Prediction of export exiting the euphotic zone was based on size-partitioning of NPP, a copepod-dominated foodweb and a ratio of 0.2 (ALOHA) and 0.1 (K2) for algal:faecal particle flux. Predicted export was 20-22 mg POC m{sup -2} d{sup -1} at ALOHA (i.e. 10-11% NPP (0-125 m); 1.1-1.2 x export flux at 150 m (E{sub 150}). At K2, export was 111 mg C m{sup -2} d{sup -1} (21% NPP (0-50 m); 1.8 x E{sub 150}) and 33 mg POC m{sup -2} d{sup -1} (11% NPP, 0-55 m); 1.4 x E{sub 150}) for deployments 1 and 2, respectively. This decrease in predicted export at K2 matches the observed trend for E{sub 150}. Also, the low attenuation of export flux from 60 to 150 m is consistent with that between 150 to 500 m. This strong surface-subsurface coupling suggests that phytoplankton productivity and floristics play a key role at K2 in setting export flux, and moreover that pelagic particle transformations by grazers strongly influence to what extent sinking particles are further broken down in the underlying waters of the Twilight Zone.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiusheng, Y., E-mail: qsyan@gdut.edu.cn; Senkai, C., E-mail: senkite@sina.com; Jisheng, P., E-mail: panjisheng@gdut.edu.cn

Different machining processes were used in the single crystal SiC wafer machining. SEM was used to observe the surface morphology and a cross-sectional cleavages microscopy method was used for subsurface cracks detection. Surface and subsurface cracks characteristics of single crystal SiC wafer in abrasive machining were analysed. The results show that the surface and subsurface cracks system of single crystal SiC wafer in abrasive machining including radial crack, lateral crack and the median crack. In lapping process, material removal is dominated by brittle removal. Lots of chipping pits were found on the lapping surface. With the particle size becomes smaller,more » the surface roughness and subsurface crack depth decreases. When the particle size was changed to 1.5µm, the surface roughness Ra was reduced to 24.0nm and the maximum subsurface crack was 1.2µm. The efficiency of grinding is higher than lapping. Plastic removal can be achieved by changing the process parameters. Material removal was mostly in brittle fracture when grinding with 325# diamond wheel. Plow scratches and chipping pits were found on the ground surface. The surface roughness Ra was 17.7nm and maximum subsurface crack depth was 5.8 µm. When grinding with 8000# diamond wheel, the material removal was in plastic flow. Plastic scratches were found on the surface. A smooth surface of roughness Ra 2.5nm without any subsurface cracks was obtained. Atomic scale removal was possible in cluster magnetorheological finishing with diamond abrasive size of 0.5 µm. A super smooth surface eventually obtained with a roughness of Ra 0.4nm without any subsurface crack.« less

Bacterial communities associated with subsurface geochemical processes in continental serpentinite springs.

PubMed

Brazelton, William J; Morrill, Penny L; Szponar, Natalie; Schrenk, Matthew O

2013-07-01

Reactions associated with the geochemical process of serpentinization can generate copious quantities of hydrogen and low-molecular-weight organic carbon compounds, which may provide energy and nutrients to sustain subsurface microbial communities independently of the photosynthetically supported surface biosphere. Previous microbial ecology studies have tested this hypothesis in deep sea hydrothermal vents, such as the Lost City hydrothermal field. This study applied similar methods, including molecular fingerprinting and tag sequencing of the 16S rRNA gene, to ultrabasic continental springs emanating from serpentinizing ultramafic rocks. These molecular surveys were linked with geochemical measurements of the fluids in an interdisciplinary approach designed to distinguish potential subsurface organisms from those derived from surface habitats. The betaproteobacterial genus Hydrogenophaga was identified as a likely inhabitant of transition zones where hydrogen-enriched subsurface fluids mix with oxygenated surface water. The Firmicutes genus Erysipelothrix was most strongly correlated with geochemical factors indicative of subsurface fluids and was identified as the most likely inhabitant of a serpentinization-powered subsurface biosphere. Both of these taxa have been identified in multiple hydrogen-enriched subsurface habitats worldwide, and the results of this study contribute to an emerging biogeographic pattern in which Betaproteobacteria occur in near-surface mixing zones and Firmicutes are present in deeper, anoxic subsurface habitats.

Bacterial Communities Associated with Subsurface Geochemical Processes in Continental Serpentinite Springs

PubMed Central

Morrill, Penny L.; Szponar, Natalie; Schrenk, Matthew O.

2013-01-01

Reactions associated with the geochemical process of serpentinization can generate copious quantities of hydrogen and low-molecular-weight organic carbon compounds, which may provide energy and nutrients to sustain subsurface microbial communities independently of the photosynthetically supported surface biosphere. Previous microbial ecology studies have tested this hypothesis in deep sea hydrothermal vents, such as the Lost City hydrothermal field. This study applied similar methods, including molecular fingerprinting and tag sequencing of the 16S rRNA gene, to ultrabasic continental springs emanating from serpentinizing ultramafic rocks. These molecular surveys were linked with geochemical measurements of the fluids in an interdisciplinary approach designed to distinguish potential subsurface organisms from those derived from surface habitats. The betaproteobacterial genus Hydrogenophaga was identified as a likely inhabitant of transition zones where hydrogen-enriched subsurface fluids mix with oxygenated surface water. The Firmicutes genus Erysipelothrix was most strongly correlated with geochemical factors indicative of subsurface fluids and was identified as the most likely inhabitant of a serpentinization-powered subsurface biosphere. Both of these taxa have been identified in multiple hydrogen-enriched subsurface habitats worldwide, and the results of this study contribute to an emerging biogeographic pattern in which Betaproteobacteria occur in near-surface mixing zones and Firmicutes are present in deeper, anoxic subsurface habitats. PMID:23584766

Nutrient loss in leachate and surface runoff from surface-broadcast and subsurface-banded broiler litter.

PubMed

Lamba, Jasmeet; Srivastava, Puneet; Way, Thomas R; Sen, Sumit; Wood, C Wesley; Yoo, Kyung H

2013-09-01

Subsurface band application of poultry litter has been shown to reduce the transport of nutrients from fields in surface runoff compared with conventional surface broadcast application. Little research has been conducted to determine the effects of surface broadcast application and subsurface banding of litter on nutrients in leachate. Therefore, a field experiment was conducted to determine the effects of subsurface band application and surface broadcast application of poultry litter on nutrient losses in leachate. Zero-tension pan and passive capillary fiberglass wick lysimeters were installed in situ 50 cm beneath the soil surface of an established tall fescue ( Schreb.) pasture on a sandy loam soil. The treatments were surface broadcast and subsurface-banded poultry litter at 5 Mg ha and an unfertilized control. Results of the rainfall simulations showed that the concentrations of PO-P and total phosphorus (TP) in leachate were reduced by 96 and 37%, respectively, in subsurface-banded litter treatment compared with the surface-applied litter treatment. There was no significant difference in PO-P concentration between control and subsurface-banded litter treatment in leachate. The trend in the loading of nutrients in leachate was similar to the trend in concentration. Concentration and loading of the nutrients (TP, PO-P, NH-N, and NO-N) in runoff from the subsurface-banded treatment were significantly less than for the surface-applied treatment and were similar to those from control plots. These results show that, compared with conventional surface broadcast application of litter, subsurface band application of litter can greatly reduce loss of P in surface runoff and leachate. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Linking Spectral Induced Polarization (SIP) and Subsurface Microbial Processes: Results from Sand Column Incubation Experiments.

PubMed

Mellage, Adrian; Smeaton, Christina M; Furman, Alex; Atekwana, Estella A; Rezanezhad, Fereidoun; Van Cappellen, Philippe

2018-02-20

Geophysical techniques, such as spectral induced polarization (SIP), offer potentially powerful approaches for in situ monitoring of subsurface biogeochemistry. The successful implementation of these techniques as monitoring tools for reactive transport phenomena, however, requires the deconvolution of multiple contributions to measured signals. Here, we present SIP spectra and complementary biogeochemical data obtained in saturated columns packed with alternating layers of ferrihydrite-coated and pure quartz sand, and inoculated with Shewanella oneidensis supplemented with lactate and nitrate. A biomass-explicit diffusion-reaction model is fitted to the experimental biogeochemical data. Overall, the results highlight that (1) the temporal response of the measured imaginary conductivity peaks parallels the microbial growth and decay dynamics in the columns, and (2) SIP is sensitive to changes in microbial abundance and cell surface charging properties, even at relatively low cell densities (<10 8 cells mL -1 ). Relaxation times (τ) derived using the Cole-Cole model vary with the dominant electron accepting process, nitrate or ferric iron reduction. The observed range of τ values, 0.012-0.107 s, yields effective polarization diameters in the range 1-3 μm, that is, 2 orders of magnitude smaller than the smallest quartz grains in the columns, suggesting that polarization of the bacterial cells controls the observed chargeability and relaxation dynamics in the experiments.

Subsurface high resolution definition of subsurface heterogeneity for understanding the biodynamics of natural field systems: Advancing the ability for scaling to field conditions. 1998 annual progress report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majer, E.L.; Brockman, F.J.

1998-06-01

'This research is an integrated physical (geophysical and hydrologic) and microbial study using innovative geophysical imaging and microbial characterization methods to identify key scales of physical heterogeneities that affect the biodynamics of natural subsurface environments. Data from controlled laboratory and in-situ experiments at the INEEL Test Area North (TAN) site are being used to determine the dominant physical characteristics (lithologic, structural, and hydrologic) that can be imaged in-situ and correlated with microbial properties. The overall goal of this research is to contribute to the understanding of the interrelationships between transport properties and spatially varying physical, chemical, and microbiological heterogeneity. Themore » outcome will be an improved understanding of the relationship between physical and microbial heterogeneity, thus facilitating the design of bioremediation strategies in similar environments. This report summarizes work as of May 1998, the second year of the project. This work is an extension of basic research on natural heterogeneity first initiated within the DOE/OHER Subsurface Science Program (SSP) and is intended to be one of the building blocks of an integrated and collaborative approach with an INEEL/PNNL effort aimed at understanding the effect of physical heterogeneity on transport properties and biodynamics in natural systems. The work is closely integrated with other EMSP projects at INEEL (Rick Colwell et al.) and PNNL (Fred Brockman and Jim Fredrickson).'« less

Thermal Impact of Medium Deep Borehole Thermal Energy Storage on the Shallow Subsurface

NASA Astrophysics Data System (ADS)

Welsch, Bastian; Schulte, Daniel O.; Rühaak, Wolfram; Bär, Kristian; Sass, Ingo

2017-04-01

Borehole heat exchanger arrays are a well-suited and already widely applied method for exploiting the shallow subsurface as seasonal heat storage. However, in most of the populated regions the shallow subsurface also comprises an important aquifer system used for drinking water production. Thus, the operation of shallow geothermal heat storage systems leads to a significant increase in groundwater temperatures in the proximity of the borehole heat exchanger array. The magnitude of the impact on groundwater quality and microbiology associated with this temperature rise is controversially discussed. Nevertheless, the protection of shallow groundwater resources has priority. Accordingly, water authorities often follow restrictive permission policies for building such storage systems. An alternative approach to avoid this issue is the application of medium deep borehole heat exchanger arrays instead of shallow ones. The thermal impact on shallow aquifers can be significantly reduced as heat is stored at larger depth. Moreover, it can be further diminished by the installation of a thermally insulating materials in the upper section of the borehole heat exchangers. Based on a numerical simulation study, the advantageous effects of medium deep borehole thermal energy storage are demonstrated and quantified. A finite element software is used to model the heat transport in the subsurface in 3D, while the heat transport in the borehole heat exchangers is solved analytically in 1D. For this purpose, an extended analytical solution is implemented, which also allows for the consideration of a thermally insulating borehole section.

Characterizing mercury concentrations and fluxes in a Coastal Plain watershed: Insights from dynamic modeling and data

USGS Publications Warehouse

Golden, H.E.; Knightes, C.D.; Conrads, P.A.; Davis, G.M.; Feaster, T.D.; Journey, C.A.; Benedict, S.T.; Brigham, M.E.; Bradley, P.M.

2012-01-01

Mercury (Hg) is one of the leading water quality concerns in surface waters of the United States. Although watershed-scale Hg cycling research has increased in the past two decades, advances in modeling watershed Hg processes in diverse physiographic regions, spatial scales, and land cover types are needed. The goal of this study was to assess Hg cycling in a Coastal Plain system using concentrations and fluxes estimated by multiple watershed-scale models with distinct mathematical frameworks reflecting different system dynamics. We simulated total mercury (HgT, the sum of filtered and particulate forms) concentrations and fluxes from a Coastal Plain watershed (McTier Creek) using three watershed Hg models and an empirical load model. Model output was compared with observed in-stream HgT. We found that shallow subsurface flow is a potentially important transport mechanism of particulate HgT during periods when connectivity between the uplands and surface waters is maximized. Other processes (e.g., stream bank erosion, sediment re-suspension) may increase particulate HgT in the water column. Simulations and data suggest that variable source area (VSA) flow and lack of rainfall interactions with surface soil horizons result in increased dissolved HgT concentrations unrelated to DOC mobilization following precipitation events. Although flushing of DOC-HgT complexes from surface soils can also occur during this period, DOC-complexed HgT becomes more important during base flow conditions. TOPLOAD simulations highlight saturated subsurface flow as a primary driver of daily HgT loadings, but shallow subsurface flow is important for HgT loads during high-flow events. Results suggest limited seasonal trends in HgT dynamics.

Characterizing mercury concentrations and fluxes in a Coastal Plain watershed: Insights from dynamic modeling and data

USGS Publications Warehouse

Golden, H.E.; Knightes, C.D.; Conrads, P.A.; Davis, G.M.; Feaster, T.D.; Journey, C.A.; Benedict, S.T.; Brigham, M.E.; Bradley, P.M.

2012-01-01

Mercury (Hg) is one of the leading water quality concerns in surface waters of the United States. Although watershed-scale Hg cycling research has increased in the past two decades, advances in modeling watershed Hg processes in diverse physiographic regions, spatial scales, and land cover types are needed. The goal of this study was to assess Hg cycling in a Coastal Plain system using concentrations and fluxes estimated by multiple watershed-scale models with distinct mathematical frameworks reflecting different system dynamics. We simulated total mercury (Hg T, the sum of filtered and particulate forms) concentrations and fluxes from a Coastal Plain watershed (McTier Creek) using three watershed Hg models and an empirical load model. Model output was compared with observed in-stream Hg T. We found that shallow subsurface flow is a potentially important transport mechanism of particulate Hg T during periods when connectivity between the uplands and surface waters is maximized. Other processes (e.g., stream bank erosion, sediment re-suspension) may increase particulate Hg T in the water column. Simulations and data suggest that variable source area (VSA) flow and lack of rainfall interactions with surface soil horizons result in increased dissolved Hg T concentrations unrelated to DOC mobilization following precipitation events. Although flushing of DOC-Hg T complexes from surface soils can also occur during this period, DOC-complexed Hg T becomes more important during base flow conditions. TOPLOAD simulations highlight saturated subsurface flow as a primary driver of daily Hg T loadings, but shallow subsurface flow is important for Hg T loads during high-flow events. Results suggest limited seasonal trends in Hg T dynamics. Copyright 2012 by the American Geophysical Union.

Continual in situ monitoring of pore water stable isotopes in the subsurface

NASA Astrophysics Data System (ADS)

Volkmann, T. H. M.; Weiler, M.

2014-05-01

Stable isotope signatures provide an integral fingerprint of origin, flow paths, transport processes, and residence times of water in the environment. However, the full potential of stable isotopes to quantitatively characterize subsurface water dynamics is yet unfolded due to the difficulty in obtaining extensive, detailed, and repeated measurements of pore water in the unsaturated and saturated zone. This paper presents a functional and cost-efficient system for non-destructive continual in situ monitoring of pore water stable isotope signatures with high resolution. Automatic controllable valve arrays are used to continuously extract diluted water vapor in soil air via a branching network of small microporous probes into a commercial laser-based isotope analyzer. Normalized liquid-phase isotope signatures are then obtained based on a specific on-site calibration approach along with basic corrections for instrument bias and temperature dependent isotopic fractionation. The system was applied to sample depth profiles on three experimental plots with varied vegetation cover in southwest Germany. Two methods (i.e., based on advective versus diffusive vapor extraction) and two modes of sampling (i.e., using multiple permanently installed probes versus a single repeatedly inserted probe) were tested and compared. The results show that the isotope distribution along natural profiles could be resolved with sufficiently high accuracy and precision at sampling intervals of less than four minutes. The presented in situ approaches may thereby be used interchangeably with each other and with concurrent laboratory-based direct equilibration measurements of destructively collected samples. It is thus found that the introduced sampling techniques provide powerful tools towards a detailed quantitative understanding of dynamic and heterogeneous shallow subsurface and vadose zone processes.

Linking Surface and Subsurface Processes: Implications for Seismic Hazards in Southern California

NASA Astrophysics Data System (ADS)

Lin, J. C.; Moon, S.; Yong, A.; Meng, L.; Martin, A. J.; Davis, P. M.

2017-12-01

Earth's surface and subsurface processes such as bedrock weathering, soil production, and river incision can influence and be influenced by spatial variations in the mechanical strength of surface material. Mechanically weakened rocks tend to have reduced seismic velocity, which can result in larger ground-motion amplification and greater potential for earthquake-induced damages. However, the influence and extent of surface and subsurface processes on the mechanical strength of surface material and seismic site conditions in southern California remain unclear. In this study, we examine whether physics-based models of surface and subsurface processes can explain the spatial variability and non-linearity of near-surface seismic velocity in southern California. We use geophysical measurements (Yong et al., 2013; Ancheta et al., 2014), consisting of shear-wave velocity (Vs) tomography data, Vs profiles, and the time-averaged Vs in the upper 30 m of the crust (Vs30) to infer lateral and vertical variations of surface material properties. Then, we compare Vs30 values with geologic and topographic attributes such as rock type, slope, elevation, and local relief, as well as metrics for surface processes such as soil production and bedrock weathering from topographic stress, frost cracking, chemical reactions, and vegetation presence. Results from this study will improve our understanding of physical processes that control subsurface material properties and their influences on local variability in seismic site conditions.

Web-based reactive transport modeling using PFLOTRAN

NASA Astrophysics Data System (ADS)

Zhou, H.; Karra, S.; Lichtner, P. C.; Versteeg, R.; Zhang, Y.

2017-12-01

Actionable understanding of system behavior in the subsurface is required for a wide spectrum of societal and engineering needs by both commercial firms and government entities and academia. These needs include, for example, water resource management, precision agriculture, contaminant remediation, unconventional energy production, CO2 sequestration monitoring, and climate studies. Such understanding requires the ability to numerically model various coupled processes that occur across different temporal and spatial scales as well as multiple physical domains (reservoirs - overburden, surface-subsurface, groundwater-surface water, saturated-unsaturated zone). Currently, this ability is typically met through an in-house approach where computational resources, model expertise, and data for model parameterization are brought together to meet modeling needs. However, such an approach has multiple drawbacks which limit the application of high-end reactive transport codes such as the Department of Energy funded[?] PFLOTRAN code. In addition, while many end users have a need for the capabilities provided by high-end reactive transport codes, they do not have the expertise - nor the time required to obtain the expertise - to effectively use these codes. We have developed and are actively enhancing a cloud-based software platform through which diverse users are able to easily configure, execute, visualize, share, and interpret PFLOTRAN models. This platform consists of a web application and available on-demand HPC computational infrastructure. The web application consists of (1) a browser-based graphical user interface which allows users to configure models and visualize results interactively, and (2) a central server with back-end relational databases which hold configuration, data, modeling results, and Python scripts for model configuration, and (3) a HPC environment for on-demand model execution. We will discuss lessons learned in the development of this platform, the rationale for different interfaces, implementation choices, as well as the planned path forward.

Sediment carbon fate in phreatic karst (Part 1): Conceptual model development

NASA Astrophysics Data System (ADS)

Husic, A.; Fox, J.; Agouridis, C.; Currens, J.; Ford, W.; Taylor, C.

2017-06-01

Recent research has paid increased attention to quantifying the fate of carbon pools within fluvial networks, but few, if any, studies consider the fate of sediment organic carbon in fluviokarst systems despite that karst landscapes cover 12% of the earth's land surface. The authors develop a conceptual model of sediment carbon fate in karst terrain with specific emphasis upon phreatic karst conduits, i.e., those located below the groundwater table that have the potential to trap surface-derived sediment and turnover carbon. To assist with their conceptual model development, the authors study a phreatic system and apply a mixture of methods traditional and novel to karst studies, including electrical resistivity imaging, well drilling, instantaneous velocimetry, dye tracing, stage recording, discrete and continuous sediment and water quality sampling, and elemental and stable carbon isotope fingerprinting. Results show that the sediment transport carrying capacity of the phreatic karst water is orders of magnitude less than surface streams during storm-activated periods promoting deposition of fine sediments in the phreatic karst. However, the sediment transport carrying capacity is sustained long after the hydrologic event has ended leading to sediment resuspension and prolonged transport. The surficial fine grained laminae occurs in the subsurface karst system; but unlike surface streams, the light-limited conditions of the subsurface karst promotes constant heterotrophy leading to carbon turnover. The coupling of the hydrological processes leads to a conceptual model that frames phreatic karst as a biologically active conveyor of sediment carbon that recharges degraded organic carbon back to surface streams. For example, fluvial sediment is estimated to lose 30% of its organic carbon by mass during a one year temporary residence within the phreatic karst. It is recommended that scientists consider karst pathways when attempting to estimate organic matter stocks and carbon transformation in fluvial networks.

Illuminating the Voluminous Subsurface Structures of Old Faithful Geyser, Yellowstone National Park

NASA Astrophysics Data System (ADS)

Hurwitz, Shaul; Shelly, David R.

2017-10-01

Old Faithful geyser in Yellowstone National Park has attracted scientific research for almost a century and a half. Temperature and pressure measurements and video recordings in the geyser's conduit led to proposals of many quantitative eruption models. Nevertheless, information on the processes that initiate the geyser's eruption in the subsurface remained limited. Two new studies, specifically Wu et al. (2017) and Ward and Lin (2017), take advantage of recent developments in seismic data acquisition technology and processing methods to illuminate subsurface structures. Using a dense array of three-component nodal geophones, these studies delineate subsurface structures on a scale larger than previously realized, which exert control on the spectacular eruptions of Old Faithful geyser.

Geo-material microfluidics at reservoir conditions for subsurface energy resource applications.

PubMed

Porter, Mark L; Jiménez-Martínez, Joaquín; Martinez, Ricardo; McCulloch, Quinn; Carey, J William; Viswanathan, Hari S

2015-10-21

Microfluidic investigations of flow and transport in porous and fractured media have the potential to play a significant role in the development of future subsurface energy resource technologies. However, the majority of experimental systems to date are limited in applicability due to operating conditions and/or the use of engineered material micromodels. We have developed a high pressure and temperature microfluidic experimental system that allows for direct observations of flow and transport within geo-material micromodels (e.g. rock, cement) at reservoir conditions. In this manuscript, we describe the experimental system, including our novel micromodel fabrication method that works in both geo- and engineered materials and utilizes 3-D tomography images of real fractures as micromodel templates to better represent the pore space and fracture geometries expected in subsurface formations. We present experimental results that highlight the advantages of using real-rock micromodels and discuss potential areas of research that could benefit from geo-material microfluidic investigations. The experiments include fracture-matrix interaction in which water imbibes into the shale rock matrix from etched fractures, supercritical CO2 (scCO2) displacing brine in idealized and realistic fracture patterns, and three-phase flow involving scCO2-brine-oil.

Accelerating Subsurface Transport Simulation on Heterogeneous Clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Villa, Oreste; Gawande, Nitin A.; Tumeo, Antonino

Reactive transport numerical models simulate chemical and microbiological reactions that occur along a flowpath. These models have to compute reactions for a large number of locations. They solve the set of ordinary differential equations (ODEs) that describes the reaction for each location through the Newton-Raphson technique. This technique involves computing a Jacobian matrix and a residual vector for each set of equation, and then solving iteratively the linearized system by performing Gaussian Elimination and LU decomposition until convergence. STOMP, a well known subsurface flow simulation tool, employs matrices with sizes in the order of 100x100 elements and, for numerical accuracy,more » LU factorization with full pivoting instead of the faster partial pivoting. Modern high performance computing systems are heterogeneous machines whose nodes integrate both CPUs and GPUs, exposing unprecedented amounts of parallelism. To exploit all their computational power, applications must use both the types of processing elements. For the case of subsurface flow simulation, this mainly requires implementing efficient batched LU-based solvers and identifying efficient solutions for enabling load balancing among the different processors of the system. In this paper we discuss two approaches that allows scaling STOMP's performance on heterogeneous clusters. We initially identify the challenges in implementing batched LU-based solvers for small matrices on GPUs, and propose an implementation that fulfills STOMP's requirements. We compare this implementation to other existing solutions. Then, we combine the batched GPU solver with an OpenMP-based CPU solver, and present an adaptive load balancer that dynamically distributes the linear systems to solve between the two components inside a node. We show how these approaches, integrated into the full application, provide speed ups from 6 to 7 times on large problems, executed on up to 16 nodes of a cluster with two AMD Opteron 6272 and a Tesla M2090 per node.« less

Fungal and Prokaryotic Activities in the Marine Subsurface Biosphere at Peru Margin and Canterbury Basin Inferred from RNA-Based Analyses and Microscopy

PubMed Central

Pachiadaki, Maria G.; Rédou, Vanessa; Beaudoin, David J.; Burgaud, Gaëtan; Edgcomb, Virginia P.

2016-01-01

The deep sedimentary biosphere, extending 100s of meters below the seafloor harbors unexpected diversity of Bacteria, Archaea, and microbial eukaryotes. Far less is known about microbial eukaryotes in subsurface habitats, albeit several studies have indicated that fungi dominate microbial eukaryotic communities and fungal molecular signatures (of both yeasts and filamentous forms) have been detected in samples as deep as 1740 mbsf. Here, we compare and contrast fungal ribosomal RNA gene signatures and whole community metatranscriptomes present in sediment core samples from 6 and 95 mbsf from Peru Margin site 1229A and from samples from 12 and 345 mbsf from Canterbury Basin site U1352. The metatranscriptome analyses reveal higher relative expression of amino acid and peptide transporters in the less nutrient rich Canterbury Basin sediments compared to the nutrient rich Peru Margin, and higher expression of motility genes in the Peru Margin samples. Higher expression of genes associated with metals transporters and antibiotic resistance and production was detected in Canterbury Basin sediments. A poly-A focused metatranscriptome produced for the Canterbury Basin sample from 345 mbsf provides further evidence for active fungal communities in the subsurface in the form of fungal-associated transcripts for metabolic and cellular processes, cell and membrane functions, and catalytic activities. Fungal communities at comparable depths at the two geographically separated locations appear dominated by distinct taxa. Differences in taxonomic composition and expression of genes associated with particular metabolic activities may be a function of sediment organic content as well as oceanic province. Microscopic analysis of Canterbury Basin sediment samples from 4 and 403 mbsf produced visualizations of septate fungal filaments, branching fungi, conidiogenesis, and spores. These images provide another important line of evidence supporting the occurrence and activity of fungi in the deep subseafloor biosphere. PMID:27375571

Fungal and Prokaryotic Activities in the Marine Subsurface Biosphere at Peru Margin and Canterbury Basin Inferred from RNA-Based Analyses and Microscopy.

PubMed

Pachiadaki, Maria G; Rédou, Vanessa; Beaudoin, David J; Burgaud, Gaëtan; Edgcomb, Virginia P

2016-01-01

The deep sedimentary biosphere, extending 100s of meters below the seafloor harbors unexpected diversity of Bacteria, Archaea, and microbial eukaryotes. Far less is known about microbial eukaryotes in subsurface habitats, albeit several studies have indicated that fungi dominate microbial eukaryotic communities and fungal molecular signatures (of both yeasts and filamentous forms) have been detected in samples as deep as 1740 mbsf. Here, we compare and contrast fungal ribosomal RNA gene signatures and whole community metatranscriptomes present in sediment core samples from 6 and 95 mbsf from Peru Margin site 1229A and from samples from 12 and 345 mbsf from Canterbury Basin site U1352. The metatranscriptome analyses reveal higher relative expression of amino acid and peptide transporters in the less nutrient rich Canterbury Basin sediments compared to the nutrient rich Peru Margin, and higher expression of motility genes in the Peru Margin samples. Higher expression of genes associated with metals transporters and antibiotic resistance and production was detected in Canterbury Basin sediments. A poly-A focused metatranscriptome produced for the Canterbury Basin sample from 345 mbsf provides further evidence for active fungal communities in the subsurface in the form of fungal-associated transcripts for metabolic and cellular processes, cell and membrane functions, and catalytic activities. Fungal communities at comparable depths at the two geographically separated locations appear dominated by distinct taxa. Differences in taxonomic composition and expression of genes associated with particular metabolic activities may be a function of sediment organic content as well as oceanic province. Microscopic analysis of Canterbury Basin sediment samples from 4 and 403 mbsf produced visualizations of septate fungal filaments, branching fungi, conidiogenesis, and spores. These images provide another important line of evidence supporting the occurrence and activity of fungi in the deep subseafloor biosphere.

Erosion, Transportation, and Deposition on Outer Solar System Satellites: Landform Evolution Modeling Studies

NASA Technical Reports Server (NTRS)

Moore, Jeffrey Morgan; Howard, Alan D.; Schenk, Paul M.

2013-01-01

Mass movement and landform degradation reduces topographic relief by moving surface materials to a lower gravitational potential. In addition to the obvious role of gravity, abrasive mechanical erosion plays a role, often in combination with the lowering of cohesion, which allows disaggregation of the relief-forming material. The identification of specific landform types associated with mass movement and landform degradation provides information about local sediment particle size and abundance and transportation processes. Generally, mass movements can be classified in terms of the particle sizes of the transported material and the speed the material moved during transport. Most degradation on outer planet satellites appears consistent with sliding or slumping, impact erosion, and regolith evolution. Some satellites, such as Callisto and perhaps Hyperion and Iapetus, have an appearance that implies that some additional process is at work, most likely sublimation-driven landform modification and mass wasting. A variant on this process is thermally driven frost segregation as seen on all three icy Galilean satellites and perhaps elsewhere. Titan is unique among outer planet satellites in that Aeolian and fluvial processes also operate to erode, transport, and deposit material. We will evaluate the sequence and extent of various landform-modifying erosional and volatile redistribution processes that have shaped these icy satellites using a 3-D model that simulates the following surface and subsurface processes: 1) sublimation and re-condensation of volatiles; 2) development of refractory lag deposits; 3) disaggregation and downward sloughing of surficial material; 4) radiative heating/cooling of the surface (including reflection, emission, and shadowing by other surface elements); 5) thermal diffusion; and 6) vapor diffusion. The model will provide explicit simulations of landform development and thusly predicts the topographic and volatile evolution of the surface and final landscape form as constrained by DEMs. We have also simulated fluvial and lacustrine modification of icy satellites landscapes to evaluate the degree to which fluvial erosion of representative initial landscapes can replicate the present Titan landscape.

Subsurface drainage processes and management impacts

Treesearch

Elizabeth T. Keppeler; David Brown

1998-01-01

Storm-induced streamflow in forested upland watersheds is linked to rainfall by transient, variably saturated flow through several different flow paths. In the absence of exposed bedrock, shallow flow-restrictive layers, or compacted soil surfaces, virtually all of the infiltrated rainfall reaches the stream as subsurface flow. Subsurface runoff can occur within...

Quantification of hydrophobic interaction affinity of colloids

NASA Astrophysics Data System (ADS)

Saini, G.; Nasholm, N.; Wood, B. D.

2009-12-01

Colloids play an important role in a wide variety of disciplines, including water and wastewater treatment, subsurface transport of metals and organic contaminants, migration of fines in oil reservoirs, biocolloid (virus and bacteria) transport in subsurface, and are integral to laboratory transport studies. Although the role of hydrophobicity in adhesion and transport of colloids, particularly bacteria, is well known; there is scarcity of literature regarding hydrophobicity measurement of non-bacterial colloids and other micron-sized particles. Here we detail an experimental approach based on differential partitioning of colloids between two liquid phases (hydrocarbon and buffer) as a measure of the hydrophobic interaction affinity of colloids. This assay, known as Microbial adhesion to hydrocarbons or MATH, is frequently used in microbiology and bacteriology for quantifying the hydrophobicity of microbes. Monodispersed colloids and particles, with sizes ranging from 1 micron to 33 micron, were used for the experiments. A range of hydrophobicity values were observed for different particles. The hydrophobicity results are also verified against water contact angle measurements of these particles. This liquid-liquid partitioning assay is quick, easy-to-perform and requires minimal instrumentation. Estimation of the hydrophobic interaction affinity of colloids would lead to a better understanding of their adhesion to different surfaces and subsequent transport in porous media.

Colloid-Mediated Transport of PPCPs through Porous Media

NASA Astrophysics Data System (ADS)

Chen, Xijuan; Xing, Yingna; Chen, Xin; Zhuang, Jie

2017-04-01

Pharmaceutical and personal care products (PPCPs) enter the soil through reclaimed water irrigation and biosolid land application. Colloids, such as clays that are present in soil, may interact with PPCPs to affect their fate and transport in the subsurface environment. This study addresses how soil colloids mediate the sorption and transport behaviors of PPCPs through laboratory column experiments. The affinities of PPCPs for colloids as well as the influence factors were investigated. For PPCPs that have high sorption (e.g., ciprofloxacin with Kd ˜104-5 L/kg) on soil colloids, the transport is dominantly controlled by colloids, with a higher extent of colloid-facilitated effect at lower ionic strength. For PPCPs that have intermediate sorption (e.g., tetracycline with Kd ˜103-4 L/kg) on soil colloids, the mobility of dissolved and colloid-bound PPCPs respond oppositely to the effect of changes in solution ionic strength, making the net effect of soil colloids on PPCP transport variable with soil solution chemistry. For PPCPs with low sorption (e.g., ibuprofen with Kd ˜102-3 L/kg) on soil colloids, other measures (such as pre-filtration) must be taken. This study suggested that colloids are significant carriers of PPCPs in the subsurface environment and could affect their off-site environmental risks.

Modelling gas transport in the shallow subsurface in the Maguelone field experiment

NASA Astrophysics Data System (ADS)

Basirat, Farzad; Niemi, Auli; Perroud, Hervé; Lofi, Johanna; Denchik, Nataliya; Lods, Gérard; Pezard, Philippe; Sharma, Prabhakar; Fagerlund, Fritjof

2013-04-01

Developing reliable monitoring techniques to detect and characterize CO2 leakage in shallow subsurface is necessary for the safety of any GCS project. To test different monitoring techniques, shallow injection-monitoring experiment have and are being carried out at the Maguelone, along the Mediterranean lido of the Gulf of Lions, near Montpellier, France. This experimental site was developed in the context of EU FP7 project MUSTANG and is documented in Lofi et al. (2012). Gas injection experiments are being carried out and three techniques of pressure, electrical resistivity and seismic monitoring have been used to detect the nitrogen and CO2 release in the near surface environment. In the present work we use the multiphase and multicomponent TOUGH2/EOS7CA model to simulate the gaseous nitrogen and CO2 transport of the experiments carried out so far. The objective is both to gain understanding of the system performance based on the model analysis as well as to further develop and validate modelling approaches for gas transport in the shallow subsurface, against the well-controlled data sets. Numerical simulation can also be used for the prediction of experimental setup limitations. We expect the simulations to represent the breakthrough time for the different tested injection rates. Based on the hydrogeological formation data beneath the lido, we also expect the vertical heterogeneities in grain size distribution create an effective capillary barrier against upward gas transport in numerical simulations. Lofi J., Pezard P.A., Bouchette F., Raynal O., Sabatier P., Denchik N., Levannier A., Dezileau L., and Certain R. Integrated onshore-offshore geophysical investigation of a layered coastal aquifer, NW Mediterranean. Ground Water, (2012).

Hydrology and subsurface transport of oil-field brine at the U.S. Geological Survey OSPER site "A", Osage County, Oklahoma

USGS Publications Warehouse

Herkelrath, W.N.; Kharaka, Y.K.; Thordsen, J.J.; Abbott, M.M.

2007-01-01

Spillage and improper disposal of saline produced water from oil wells has caused environmental damage at thousands of sites in the United States. In order to improve understanding of the fate and transport of contaminants at these sites, the U.S. Geological Survey carried out multidisciplinary investigations at two oil production sites near Skiatook Lake, Oklahoma. As a part of this effort, the hydrology and subsurface transport of brine at OSPER site "A", a tank battery and pit complex that was abandoned in 1973, was investigated. Based on data from 41 new boreholes that were cored and completed with monitoring wells, a large (???200 m ?? 200 m ?? 20 m) plume of saline ground water was mapped. The main dissolved species are Na and Cl, with TDS in the plume ranging as high as 30,000 mg/L. Analysis of the high barometric efficiency of the wells indicated a confined aquifer response. Well-slug tests indicated the hydraulic conductivity is low (0.3-7.0 cm/day). Simplified flow and transport modeling supports the following conceptual model: (1) prior to the produced water releases, recharge was generally low (???1 cm/a); (2) in ???60 a of oil production enough saline produced water in pits leaked into the subsurface to create the plume; (3) following abandonment of the site in 1973 and filling of Skiatook Reservoir in the mid-1980s, recharge and lateral flow of water through the plume returned to low values; (4) as a result, spreading of the brine plume caused by mixing with fresh ground water recharge, as well as natural attenuation, are very slow.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Catalano, Jeffrey G.; Giammar, Daniel E.; Wang, Zheming

Phosphate addition is an in situ remediation approach that may enhance the sequestration of uranium without requiring sustained reducing conditions. However, the geochemical factors that determine the dominant immobilization mechanisms upon phosphate addition are insufficiently understood to design efficient remediation strategies or accurately predict U(VI) transport. The overall objective of our project is to determine the dominant mechanisms of U(VI)-phosphate reactions in subsurface environments. Our research approach seeks to determine the U(VI)-phosphate solid that form in the presence of different groundwater cations, characterize the effects of phosphate on U(VI) adsorption and precipitation on smectite and iron oxide minerals, examples ofmore » two major reactive mineral phases in contaminated sediments, and investigate how phosphate affects U(VI) speciation and fate during water flow through sediments from contaminated sites. The research activities conducted for this project have generated a series of major findings. U(VI) phosphate solids from the autunite mineral family are the sole phases to form during precipitation, with uranyl orthophosphate not occurring despite its predicted greater stability. Calcium phosphates may take up substantial quantities of U(VI) through three different removal processes (adsorption, coprecipitation, and precipitation) but the dominance of each process varies with the pathway of reaction. Phosphate co-adsorbs with U(VI) onto smectite mineral surfaces, forming a mixed uranium-phosphate surface complex over a wide range of conditions. However, this molecular-scale association of uranium and phosphate has not effect on the overall extent of uptake. In contrast, phosphate enhanced U(VI) adsorption to iron oxide minerals at acidic pH conditions but suppresses such adsorption at neutral and alkaline pH, despite forming mixed uranium-phosphate surface complexes during adsorption. Nucleation barriers exist that inhibit U(VI) phosphate solids from precipitating in the presence of smectite and iron oxide minerals as well as sediments from contaminated sites. Phosphate addition enhances retention of U(VI) by sediments from the Rifle, CO and Hanford, WA field research sites, areas containing substantial uranium contamination of groundwater. This enhanced retention is through adsorption processes. Both fast and slow uptake and release behavior is observed, indicating that diffusion of uranium between sediment grains has a substantial effect of U(VI) fate in flowing groundwater systems. This project has revealed the complexity of U(VI)-phosphate reactions in subsurface systems. Distinct chemical processes occur in acidic and alkaline groundwater systems. For the latter, calcium phosphate formation, solution complexation, and competition between phosphate and uranium for adsorption sites may serve to either enhance or inhibit U(VI) removal from groundwater. Under the groundwater conditions present at many contaminated sites in the U.S., phosphate appears to general enhance U(VI) retention and limit transport. However, formation of low-solubility uranium phosphate solids does not occur under field-relevant conditions, despite this being the desired product of phosphate-based remediation approaches. In addition, simple equilibrium approaches fail to well-predict uranium fate in contaminated sediments amended with phosphate, with reactive transport models that include reaction rates and mass transport through occluded domains needed to properly describe the system. Phosphate addition faces challenges to being effective as a stand-alone groundwater treatment approach but would prove beneficial as an add-on to other treatment methods that will further limit uranium migration in the subsurface.« less

Final Report - Montana State University - Microbial Activity and Precipitation at Solution-Solution Mixing Zones in Porous Media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerlach, Robin

Background. The use of biological and chemical processes that degrade or immobilize contaminants in subsurface environments is a cornerstone of remediation technology. The enhancement of biological and chemical processes in situ, involves the transport, displacement, distribution and mixing of one or more reactive agents. Biological and chemical reactions all require diffusive transport of solutes to reaction sites at the molecular scale and accordingly, the success of processes at the meter-scale and larger is dictated by the success of phenomena that occur at the micron-scale. However, current understanding of scaling effects on the mixing and delivery of nutrients in biogeochemically dynamicmore » porous media systems is limited, despite the limitations this imposes on the efficiency and effectiveness of the remediation challenges at hand. Objectives. We therefore proposed to experimentally characterize and computationally describe the growth, evolution, and distribution of microbial activity and mineral formation as well as changes in transport processes in porous media that receive two or more reactive amendments. The model system chosen for this project was based on a method for immobilizing 90Sr, which involves stimulating microbial urea hydrolysis with ensuing mineral precipitation (CaCO3), and co-precipitation of Sr. Studies at different laboratory scales were used to visualize and quantitatively describe the spatial relationships between amendment transport and consumption that stimulate the production of biomass and mineral phases that subsequently modify the permeability and heterogeneity of porous media. Biomass growth, activity, and mass deposition in mixing zones was investigated using two-dimensional micro-model flow cells as well as flow cells that could be analyzed using synchrotron-based x-ray tomography. Larger-scale flow-cell experiments were conducted where the spatial distribution of media properties, flow, segregation of biological activity and impact on ancillary constituents (i.e., Sr) was determined. Model simulations accompanied the experimental efforts. Benefits and Outcomes of the Project. The research contributed towards defining the key physical, chemical, and biological processes influencing the form and mobility of DOE priority contaminants (e.g., 60Co, 90Sr, U) in the subsurface. The work conducted and reported herein, will in the future (i) contribute to controlling the juxtaposition of microbial activity, contaminants and amendments, (ii) promote new strategies for delivering amendments, and (iii) allow new approaches for modifying permeability and flow in porous media. We feel that the work has already translated directly to improving the efficiency of amendment based remediation strategies. Products. The results of the project have been published in a number of peer reviewed journal articles. The abstracts and citations to those articles, given in section 2.0 below, make up the bulk of this final report.« less

Thermal management of an unconsolidated shallow urban groundwater body

NASA Astrophysics Data System (ADS)

Epting, J.; Händel, F.; Huggenberger, P.

2013-05-01

This study presents the development of tools for the sustainable thermal management of a shallow unconsolidated urban groundwater body in the city of Basel (Switzerland). The concept of the investigations is based on (1) a characterization of the present thermal state of the urban groundwater body, and (2) the evaluation of potential mitigation measures for the future thermal management of specific regions within the groundwater body. The investigations focus on thermal processes down-gradient of thermal groundwater use, effects of heated buildings in the subsurface as well as the thermal influence of river-groundwater interaction. Investigation methods include (1) short- and long-term data analysis, (2) high-resolution multilevel groundwater temperature monitoring, as well as (3) 3-D numerical groundwater flow and heat transport modeling and scenario development. The combination of these methods allows for the quantifying of the thermal influences on the investigated urban groundwater body, including the influences of thermal groundwater use and heated subsurface constructions. Subsequently, first implications for management strategies are discussed, including minimizing further groundwater temperature increase, targeting "potential natural" groundwater temperatures for specific aquifer regions and exploiting the thermal potential.

Analytical solutions for efficient interpretation of single-well push-pull tracer tests

NASA Astrophysics Data System (ADS)

Huang, Junqi; Christ, John A.; Goltz, Mark N.

2010-08-01

Single-well push-pull tracer tests have been used to characterize the extent, fate, and transport of subsurface contamination. Analytical solutions provide one alternative for interpreting test results. In this work, an exact analytical solution to two-dimensional equations describing the governing processes acting on a dissolved compound during a modified push-pull test (advection, longitudinal and transverse dispersion, first-order decay, and rate-limited sorption/partitioning in steady, divergent, and convergent flow fields) is developed. The coupling of this solution with inverse modeling to estimate aquifer parameters provides an efficient methodology for subsurface characterization. Synthetic data for single-well push-pull tests are employed to demonstrate the utility of the solution for determining (1) estimates of aquifer longitudinal and transverse dispersivities, (2) sorption distribution coefficients and rate constants, and (3) non-aqueous phase liquid (NAPL) saturations. Employment of the solution to estimate NAPL saturations based on partitioning and non-partitioning tracers is designed to overcome limitations of previous efforts by including rate-limited mass transfer. This solution provides a new tool for use by practitioners when interpreting single-well push-pull test results.

Using electrokinetic phenomena and electrical resistance tomography to characterize the movement of subsurface fluids

DOEpatents

Ramirez, Abelardo L.; Cooper, John F.; Daily, William D.

1996-01-01

This invention relates generally to the remote detections of subsurface liquid contaminants using in combination a geophysical technique known as ERT and an EKS. Electrokinetic transport is used to enhance the ability of electrical resistance tomography (ERT) to detect position and movement of subsurface contaminant liquids, particles or ions. ERT images alone are difficult to interpret because of natural inhomogeneities in soil composition and electrical properties. By subtracting two or more ERT images obtained before and after field induced movement, a high contrast image of a plume of distinct electrokinetic properties can be seen. The invention is applicable to important subsurface characterization problems including, as examples, (1) detection of liquid-saturated plumes of contaminants such as those associated with leaks from underground storage tanks containing hazardous concentrated electrolytes, (2) detection and characterization of soils contaminated with organic pollutants such as droplets of gasoline; and (3) monitoring the progress of electrokinetic containment or clean up of underground contamination.

Using electrokinetic phenomena and electrical resistance tomography to characterize the movement of subsurface fluids

DOEpatents

Ramirez, A.L.; Cooper, J.F.; Daily, W.D.

1996-02-27

This invention relates generally to the remote detections of subsurface liquid contaminants using in combination a geophysical technique known as ERT and an EKS. Electrokinetic transport is used to enhance the ability of electrical resistance tomography (ERT) to detect position and movement of subsurface contaminant liquids, particles or ions. ERT images alone are difficult to interpret because of natural inhomogeneities in soil composition and electrical properties. By subtracting two or more ERT images obtained before and after field induced movement, a high contrast image of a plume of distinct electrokinetic properties can be seen. The invention is applicable to important subsurface characterization problems including, as examples, (1) detection of liquid-saturated plumes of contaminants such as those associated with leaks from underground storage tanks containing hazardous concentrated electrolytes, (2) detection and characterization of soils contaminated with organic pollutants such as droplets of gasoline; and (3) monitoring the progress of electrokinetic containment or clean up of underground contamination. 1 fig.

FINAL REPORT: Mechanistically-Base Field Scale Models of Uranium Biogeochemistry from Upscaling Pore-Scale Experiments and Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wood, Brian D.

2013-11-04

Biogeochemical reactive transport processes in the subsurface environment are important to many contemporary environmental issues of significance to DOE. Quantification of risks and impacts associated with environmental management options, and design of remediation systems where needed, require that we have at our disposal reliable predictive tools (usually in the form of numerical simulation models). However, it is well known that even the most sophisticated reactive transport models available today have poor predictive power, particularly when applied at the field scale. Although the lack of predictive ability is associated in part with our inability to characterize the subsurface and limitations inmore » computational power, significant advances have been made in both of these areas in recent decades and can be expected to continue. In this research, we examined the upscaling (pore to Darcy and Darcy to field) the problem of bioremediation via biofilms in porous media. The principle idea was to start with a conceptual description of the bioremediation process at the pore scale, and apply upscaling methods to formally develop the appropriate upscaled model at the so-called Darcy scale. The purpose was to determine (1) what forms the upscaled models would take, and (2) how one might parameterize such upscaled models for applications to bioremediation in the field. We were able to effectively upscale the bioremediation process to explain how the pore-scale phenomena were linked to the field scale. The end product of this research was to produce a set of upscaled models that could be used to help predict field-scale bioremediation. These models were mechanistic, in the sense that they directly incorporated pore-scale information, but upscaled so that only the essential features of the process were needed to predict the effective parameters that appear in the model. In this way, a direct link between the microscale and the field scale was made, but the upscaling process helped inform potential users of the model what kinds of information would be needed to accurately characterize the system.« less

Transport of Carbon Tetrachloride in a Fractured Vadose Zone due to Atmospheric Pressure Fluctuations, Diffusion, and Vapor Density

NASA Astrophysics Data System (ADS)

McCray, J. E.; Downs, W.; Falta, R. W.; Housley, T.

2005-12-01

DNAPL sources of carbon tetrachloride (CT) vapors are of interest at the Radioactive Waste Management Complex (RWMC) at the Idaho National Engineering and Environmental Laboratory (INEEL). The site is underlain by thick fractured basalt that includes sedimentary interbeds, each are a few meters thick. Daily atmospheric pressure fluctuations serve as driving forces for CT vapor transport in the subsurface. Other important transport processes for vapor movement include gas-phase diffusion and density-driven transport. The objective of this research is to investigate the influence and relative importance of these processes on gaseous transport of CT. Gas pressure and vapor concentration measurements were conducted at various depths in two wells. A numerical multiphase flow model (TOUGH2), calibrated to field pressure data, is used to conduct sensitivity analyses to elucidate the importance of the different transport mechanisms. Results show that the basalt is highly permeable to vertical air flow. The pressure dampening occurs mainly in the sedimentary interbeds. Model-calibrated permeability values for the interbeds are similar to those obtained in a study by the U.S. Geological Survey for shallow sediments, and an order of magnitude higher than column-scale values obtained by previous studies conducted by INEEL scientists. The transport simulations indicate that considering the effect of barometric pressure changes is critical to simulating transport of pollutants in the vadose zone above the DNAPL source. Predicted concentrations can be orders of magnitude smaller than actual concentrations if the effect is not considered. Below the DNAPL vapor source, accounting for density and diffusion alone would yield acceptable results provided that a 20% error in concentrations are acceptable, and that simulating concentrations trends (and not actual concentrations) is the primary goal.

Using a spatially-distributed hydrologic biogeochemistry model to study the spatial variation of carbon processes in a Critical Zone Observatory

NASA Astrophysics Data System (ADS)

Shi, Y.; Eissenstat, D. M.; Davis, K. J.; He, Y.

2016-12-01

Forest carbon processes are affected by, among other factors, soil moisture, soil temperature, soil nutrients and solar radiation. Most of the current biogeochemical models are 1-D and represent one point in space. Therefore, they cannot resolve the topographically driven hill-slope land surface heterogeneity or the spatial pattern of nutrient availability. A spatially distributed forest ecosystem model, Flux-PIHM-BGC, has been developed by coupling a 1-D mechanistic biogeochemical model Biome-BGC (BBGC) with a spatially distributed land surface hydrologic model, Flux-PIHM. Flux-PIHM is a coupled physically based model, which incorporates a land-surface scheme into the Penn State Integrated Hydrologic Model (PIHM). The land surface scheme is adapted from the Noah land surface model. Flux-PIHM is able to represent the link between groundwater and the surface energy balance, as well as the land surface heterogeneities caused by topography. In the coupled Flux-PIHM-BGC model, each Flux-PIHM model grid couples a 1-D BBGC model, while soil nitrogen is transported among model grids via subsurface water flow. In each grid, Flux-PIHM provides BBGC with soil moisture, soil temperature, and solar radiation information, while BBGC provides Flux-PIHM with leaf area index. The coupled Flux-PIHM-BGC model has been implemented at the Susquehanna/Shale Hills critical zone observatory (SSHCZO). Model results suggest that the vegetation and soil carbon distribution is primarily constrained by nitorgen availability (affected by nitorgen transport via topographically driven subsurface flow), and also constrained by solar radiation and root zone soil moisture. The predicted vegetation and soil carbon distribution generally agrees with the macro pattern observed within the watershed. The coupled ecosystem-hydrologic model provides an important tool to study the impact of topography on watershed carbon processes, as well as the impact of climate change on water resources.

THC-MP: High performance numerical simulation of reactive transport and multiphase flow in porous media

NASA Astrophysics Data System (ADS)

Wei, Xiaohui; Li, Weishan; Tian, Hailong; Li, Hongliang; Xu, Haixiao; Xu, Tianfu

2015-07-01

The numerical simulation of multiphase flow and reactive transport in the porous media on complex subsurface problem is a computationally intensive application. To meet the increasingly computational requirements, this paper presents a parallel computing method and architecture. Derived from TOUGHREACT that is a well-established code for simulating subsurface multi-phase flow and reactive transport problems, we developed a high performance computing THC-MP based on massive parallel computer, which extends greatly on the computational capability for the original code. The domain decomposition method was applied to the coupled numerical computing procedure in the THC-MP. We designed the distributed data structure, implemented the data initialization and exchange between the computing nodes and the core solving module using the hybrid parallel iterative and direct solver. Numerical accuracy of the THC-MP was verified through a CO2 injection-induced reactive transport problem by comparing the results obtained from the parallel computing and sequential computing (original code). Execution efficiency and code scalability were examined through field scale carbon sequestration applications on the multicore cluster. The results demonstrate successfully the enhanced performance using the THC-MP on parallel computing facilities.

Assessing the value of different data sets and modeling schemes for flow and transport simulations

NASA Astrophysics Data System (ADS)

Hyndman, D. W.; Dogan, M.; Van Dam, R. L.; Meerschaert, M. M.; Butler, J. J., Jr.; Benson, D. A.

2014-12-01

Accurate modeling of contaminant transport has been hampered by an inability to characterize subsurface flow and transport properties at a sufficiently high resolution. However mathematical extrapolation combined with different measurement methods can provide realistic three-dimensional fields of highly heterogeneous hydraulic conductivity (K). This study demonstrates an approach to evaluate the time, cost, and efficiency of subsurface K characterization. We quantify the value of different data sets at the highly heterogeneous Macro Dispersion Experiment (MADE) Site in Mississippi, which is a flagship test site that has been used for several macro- and small-scale tracer tests that revealed non-Gaussian tracer behavior. Tracer data collected at the site are compared to models that are based on different types and resolution of geophysical and hydrologic data. We present a cost-benefit analysis of several techniques including: 1) flowmeter K data, 2) direct-push K data, 3) ground penetrating radar, and 4) two stochastic methods to generate K fields. This research provides an initial assessment of the level of data necessary to accurately simulate solute transport with the traditional advection dispersion equation; it also provides a basis to design lower cost and more efficient remediation schemes at highly heterogeneous sites.

The origin of anomalous transport in porous media - is it possible to make a priori predictions?

NASA Astrophysics Data System (ADS)

Bijeljic, Branko; Blunt, Martin

2013-04-01

Despite the range of significant applications of flow and solute transport in porous rock, including contaminant migration in subsurface hydrology, geological storage of carbon-dioxide and tracer studies and miscible displacement in oil recovery, even the qualitative behavior in the subsurface is uncertain. The non-Fickian nature of dispersive processes in heterogeneous porous media has been demonstrated experimentally from pore to field scales. However, the exact relationship between structure, velocity field and transport has not been fully understood. Advances in X ray imaging techniques made it possible to accurately describe structure of the pore space, helping predict flow and anomalous transport behaviour using direct simulation. This is demonstrated by simulating solute transport through 3D images of rock samples, with resolutions of a few microns, representing geological media of increasing pore-scale complexity: a sandpack, a sandstone, and a carbonate. A novel methodology is developed that predicts solute transport at the pore scale by using probability density functions of displacement (propagators) and probability density function of transit time between the image voxels, and relates it to probability density function of normalized local velocity. A key advantage is that full information on velocity and solute concentration is retained in the models. The methodology includes solving for Stokes flow by Open Foam, solving for advective transport by the novel streamline simulation method, and superimposing diffusive transport diffusion by the random walk method. It is shown how computed propagators for beadpack, sandstone and carbonate depend on the spread in the velocity distribution. A narrow velocity distribution in the beadpack leads to the least anomalous behaviour where the propagators rapidly become Gaussian; the wider velocity distribution in the sandstone gives rise to a small immobile concentration peak, and a large secondary mobile peak moving at approximately the average flow speed; in the carbonate with the widest velocity distribution the stagnant concentration peak is persistent, while the emergence of a smaller secondary mobile peak is observed, leading to a highly anomalous behavior. This defines different generic nature of non-Fickian transport in the three media and quantifies the effect of pore structure on transport. Moreover, the propagators obtained by the model are in a very good agreement with the propagators measured on beadpack, Bentheimer sandstone and Portland carbonate cores in nuclear magnetic resonance experiments. These findings demonstrate that it is possible to make a priori predictions of anomalous transport in porous media. The importance of these findings for transport in complex carbonate rock micro-CT images is discussed, classifying them in terms of degree of anomalous transport that can have an impact at the field scale. Extensions to reactive transport will be discussed.

Influence of bedrock topography on the runoff generation under use of ERT data

NASA Astrophysics Data System (ADS)

Kiese, Nina; Loritz, Ralf; Allroggen, Niklas; Zehe, Erwin

2017-04-01

Subsurface topography has been identified to play a major role for the runoff generation in different hydrological landscapes. Sinks and ridges in the bedrock can control how water is stored and transported to the stream. Detecting the subsurface structure is difficult and laborious and frequently done by auger measurements. Recently, the geophysical imaging of the subsurface by Electrical Resistivity Tomography (ERT) gained much interest in the field of hydrology, as it is a non-invasive method to collect information on the subsurface characteristics and particularly bedrock topography. As it is impossible to characterize the subsurface of an entire hydrological landscape using ERT, it is of key interest to identify the bedrock characteristics which dominate runoff generation to adapt and optimize the sampling design to the question of interest. For this study, we used 2D ERT images and auger measurements, collected on different sites in the Attert basin in Luxembourg, to characterize bedrock topography using geostatistics and shed light on those aspects which dominate runoff generation. Based on ERT images, we generated stochastic bedrock topographies and implemented them in a physically-based 2D hillslope model. With this approach, we were able to test the influence of different subsurface structures on the runoff generation. Our results highlight that ERT images can be useful for hydrological modelling. Especially the connection from the hillslope to the stream could be identified as important feature in the subsurface for the runoff generation whereas the microtopography of the bedrock seemed to be less relevant.

Virtual experiments: a new approach for improving process conceptualization in hillslope hydrology

NASA Astrophysics Data System (ADS)

Weiler, Markus; McDonnell, Jeff

2004-01-01

We present an approach for process conceptualization in hillslope hydrology. We develop and implement a series of virtual experiments, whereby the interaction between water flow pathways, source and mixing at the hillslope scale is examined within a virtual experiment framework. We define these virtual experiments as 'numerical experiments with a model driven by collective field intelligence'. The virtual experiments explore the first-order controls in hillslope hydrology, where the experimentalist and modeler work together to cooperatively develop and analyze the results. Our hillslope model for the virtual experiments (HillVi) in this paper is based on conceptualizing the water balance within the saturated and unsaturated zone in relation to soil physical properties in a spatially explicit manner at the hillslope scale. We argue that a virtual experiment model needs to be able to capture all major controls on subsurface flow processes that the experimentalist might deem important, while at the same time being simple with few 'tunable parameters'. This combination makes the approach, and the dialog between experimentalist and modeler, a useful hypothesis testing tool. HillVi simulates mass flux for different initial conditions under the same flow conditions. We analyze our results in terms of an artificial line source and isotopic hydrograph separation of water and subsurface flow. Our results for this first set of virtual experiments showed how drainable porosity and soil depth variability exert a first order control on flow and transport at the hillslope scale. We found that high drainable porosity soils resulted in a restricted water table rise, resulting in more pronounced channeling of lateral subsurface flow along the soil-bedrock interface. This in turn resulted in a more anastomosing network of tracer movement across the slope. The virtual isotope hydrograph separation showed higher proportions of event water with increasing drainable porosity. When combined with previous experimental findings and conceptualizations, virtual experiments can be an effective way to isolate certain controls and examine their influence over a range of rainfall and antecedent wetness conditions.

Influences of Coupled Hydrologic and Microbial Processes on River Corridor Biogeochemistry and Ecology

NASA Astrophysics Data System (ADS)

Scheibe, T. D.; Song, H. S.; Stegen, J.; Graham, E.; Bao, J.; Goldman, A.; Zhou, T.; Crump, A.; Hou, Z.; Hammond, G. E.; Chen, X.; Huang, M.; Zhang, X.; Nelson, W. C.; Garayburu-Caruso, V. A.

2017-12-01

The exchange of water between rivers and surrounding subsurface environments (hydrologic exchange flows or HEFs) is a vital aspect of river ecology and watershed function. HEFs play a key role in water quality, nutrient cycling, and ecosystem health, and they modulate water temperatures and enhance exchange of terrestrial and aquatic nutrients, which lead to elevated biogeochemical activity. However, these coupled hydrologic and microbiological processes are not well understood, particularly in the context of large managed river systems with highly variable discharge, and are poorly represented in system-scale quantitative models. Using the 75 km Hanford Reach of the Columbia River as the research domain, we apply high-resolution flow simulations supported by field observations to understand how variable river discharge interacts with hydromorphic and hydrogeologic structures to generate HEFs and distributions of subsurface residence times. We combine this understanding of hydrologic processes with microbiological activity measurements and reactive transport models to elucidate the holistic impacts of variable discharge on river corridor (surface and subsurface) ecosystems. In particular, our project seeks to develop and test new conceptual and numerical models that explicitly incorporate i) the character (chemical speciation and thermodynamics) of natural organic matter as it varies along flow paths and through mixing of groundwater and surface water, and ii) the history-dependent response of microbial communities to varying time scales of inundation associated with fluctuations in river discharge. The results of these high-resolution mechanistic models are guiding formulation and parameterization of reduced-order models applicable at reach to watershed scales. New understanding of coupled hydrology and microbiology in the river corridor will play a key role in reduction of uncertainties associated with major Earth system biogeochemical fluxes, improving predictions of environmental and human impacts on water quality and riverine ecosystems, and supporting environmentally responsible management of linked energy-water systems.

Measuring Subsurface Water Fluxes Using a Heat Pulse Sensor

NASA Astrophysics Data System (ADS)

Ochsner, T. E.; Wang, Q.; Horton, R.

2001-12-01

Subsurface water flux is an important parameter in studies of runoff, infiltration, groundwater recharge, and subsurface chemical transport. Heat pulse sensors have been proposed as promising tools for measuring subsurface water fluxes. Our heat pulse probe consists of three 4-cm stainless-steel needles embedded in a waterproof epoxy body. The needles contain resistance heaters and thermocouples. The probes are connected to an external datalogger and power supply and then installed in soil. To measure the water flux, a 15-s heat pulse is generated at the middle needle using the power supply and the resistance heater, and the temperature increases at the needles 6-mm upstream and downstream from the heater are recorded using the thermocouples and datalogger. To date, heat pulse methods have required cumbersome mathematical analysis to calculate soil water flux from this measured data. We present a new mathematical analysis showing that a simple relationship exists between water flux and the ratio of the temperature increase downstream from the line heat source to the temperature increase upstream from the line heat source. The simplicity of this relationship makes heat pulse sensors a more attractive option for measuring subsurface water fluxes.

Colloid mobilization and heavy metal transport in the sampling of soil solution from Duckum soil in South Korea.

PubMed

Lee, Seyong; Ko, Il-Won; Yoon, In-Ho; Kim, Dong-Wook; Kim, Kyoung-Woong

2018-03-24

Colloid mobilization is a significant process governing colloid-associated transport of heavy metals in subsurface environments. It has been studied for the last three decades to understand this process. However, colloid mobilization and heavy metal transport in soil solutions have rarely been studied using soils in South Korea. We investigated the colloid mobilization in a variety of flow rates during sampling soil solutions in sand columns. The colloid concentrations were increased at low flow rates and in saturated regimes. Colloid concentrations increased 1000-fold higher at pH 9.2 than at pH 7.3 in the absence of 10 mM NaCl solution. In addition, those were fourfold higher in the absence than in the presence of the NaCl solution at pH 9.2. It was suggested that the mobility of colloids should be enhanced in porous media under the basic conditions and the low ionic strength. In real field soils, the concentrations of As, Cr, and Pb in soil solutions increased with the increase in colloid concentrations at initial momentarily changed soil water pressure, whereas the concentrations of Cd, Cu, Fe, Ni, Al, and Co lagged behind the colloid release. Therefore, physicochemical changes and heavy metal characteristics have important implications for colloid-facilitated transport during sampling soil solutions.

Pathways and transformations of dissolved methane and dissolved inorganic carbon in Arctic tundra watersheds: Evidence from analysis of stable isotopes

DOE PAGES

Throckmorton, Heather M.; Heikoop, Jeffrey M.; Newman, Brent D.; ...

2015-11-08

Arctic soils contain a large pool of terrestrial C and are of interest due to their potential for releasing significant carbon dioxide (CO 2) and methane (CH 4) to the atmosphere. Due to substantial landscape heterogeneity, predicting ecosystem-scale CH 4 and CO 2 production is challenging. This study assessed dissolved inorganic carbon (DIC = Σ (total) dissolved CO 2) and CH 4 in watershed drainages in Barrow, Alaska as critical convergent zones of regional geochemistry, substrates, and nutrients. In July and September of 2013, surface waters and saturated subsurface pore waters were collected from 17 drainages. Based on simultaneous DICmore » and CH 4 cycling, we synthesized isotopic and geochemical methods to develop a subsurface CH 4 and DIC balance by estimating mechanisms of CH 4 and DIC production and transport pathways and oxidation of subsurface CH 4. We observed a shift from acetoclastic (July) toward hydrogenotropic (September) methanogenesis at sites located toward the end of major freshwater drainages, adjacent to salty estuarine waters, suggesting an interesting landscape-scale effect on CH 4 production mechanism. The majority of subsurface CH 4 was transported upward by plant-mediated transport and ebullition, predominantly bypassing the potential for CH 4 oxidation. Thus, surprisingly, CH 4 oxidation only consumed approximately 2.51± 0.82% (July) and 0.79 ± 0.79% (September) of CH 4 produced at the frost table, contributing to <0.1% of DIC production. DIC was primarily produced from respiration, with iron and organic matter serving as likely e- acceptors. Furthermore, this work highlights the importance of spatial and temporal variability of CH 4 production at the watershed scale and suggests broad scale investigations are required to build better regional or pan-Arctic representations of CH 4 and CO 2 production.« less

Enhanced permanganate in situ chemical oxidation through MnO2 particle stabilization: evaluation in 1-D transport systems.

PubMed

Crimi, Michelle; Quickel, Mark; Ko, Saebom

2009-02-27

In situ chemical oxidation using permanganate is an increasingly employed approach to organic contaminant remediation at hazardous waste sites. Manganese dioxide (MnO2) particles form as a by-product of the reaction of permanganate with contaminants and naturally-reduced subsurface materials. These particles are of interest because they have the potential to deposit in the subsurface and impact the flow regime in/around permanganate injection, including the well screen, filter pack, and the surrounding subsurface formation. Control of these particles can allow for improved oxidant injection and transport, and contact between the oxidant and contaminants of concern. Sodium hexametaphosphate (HMP) has previously been identified as a promising aid to stabilize MnO2 in solution when included in the oxidizing solution, increasing the potential to inhibit particle deposition and impact subsurface flow. The goal of the experimental studies described herein was to investigate the ability of HMP to prevent particle deposition in transport studies using four different types of porous media. Permanganate was delivered to a contaminant source zone (trichloroethylene) located within four different media types with variations in sand, clay, organic carbon, and iron oxides (as goethite) content. Deposition of MnO2 within the columns was quantified with distance from the source zone. Experiments were repeated in replicate columns with the inclusion of HMP directly with the oxidant delivery solution, and MnO2 deposition was again quantified. While total MnO2 deposition within the 60 cm columns did not change significantly with the addition of HMP, deposition within the contaminant source zone decreased by 25-85%, depending on the specific media type. The greatest differences in deposition were observed in the goethite-containing and clay-containing columns. Columns containing these two media types experienced completely plugged flow in the oxidant-only delivery systems; however, the addition of HMP prevented this plugging within the columns, increasing the oxidant throughput.

Experimental determination of methane dissolution from simulated subsurface oil leakages

NASA Astrophysics Data System (ADS)

Sauthoff, W.; Peltzer, E. T.; Walz, P. M.; Brewer, P. G.

2013-12-01

Subsurface oil leakages and increased offshore drilling efforts have raised concern over the fate of hydrocarbon mixtures of oil and gas in ocean environments. Recent wellhead and pipeline failures in the Gulf of Mexico are extreme examples of this problem. Understanding the mechanism and rate of vertical transport of hydrocarbon chemical species is necessary to predict the environmental impact of subsurface leakages. In a series of controlled experiments, we carried out a deep-sea field experiment in Monterey Canyon to investigate the behavior of a gas-saturated liquid hydrocarbon mass rising from the seafloor. Aboard the R/V Rachel Carson, we used the ROV Ventana to transport a laboratory prepared volume of decane (C10H22) saturated with methane gas (CH4) to mimic a subsurface seafloor discharge. We released the oil and gas mixture into a vertically oriented open bottom glass tube followed by methane loss rate measurements both at discrete depths, and during rapid, continuous vehicle ascent from 800 to 100 m water depth to monitor changes in dissolution and bubble nucleation. Using laser Raman techniques and HD video we quantified the chemical state of the hydrocarbon fluid, including rate of methane gas dissolution. The primary methane Raman peak was readily observable within the decane C-H stretching complex. Variation in the amount of gas dissolved in the oil greatly influences oil plume density and in turn oil plume vertical rise rate. Our results show that the rise rate of the hydrocarbon mass significantly exceeds the rate at which the excess methane was lost by dissolution. This result implies that vertical transport of methane in the saturated hydrocarbon liquid phase can greatly exceed a gas bubble plume ascending the water column from a seafloor source. These results and observations may be applicable to improved understanding of the composition, distribution, and environmental fate of leaked hydrocarbon mixtures and inform remediation efforts.

Mobility of Source Zone Heavy Metals and Radionuclides: The Mixed Roles of Fermentative Activity on Fate and Transport of U and Cr. Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerlach, Robin; Peyton, Brent M.; Apel, William A.

2014-01-29

Various U. S. Department of Energy (DOE) low and medium-level radioactive waste sites contain mixtures of heavy metals, radionuclides and assorted organic materials. In addition, there are numerous sites around the world that are contaminated with a mixture of organic and inorganic contaminants. In most sites, over time, water infiltrates the wastes, and releases metals, radionuclides and other contaminants causing transport into the surrounding environment. We investigated the role of fermentative microorganisms in such sites that may control metal, radionuclide and organics migration from source zones. The project was initiated based on the following overarching hypothesis: Metals, radionuclides and othermore » contaminants can be mobilized by infiltration of water into waste storage sites. Microbial communities of lignocellulose degrading and fermenting microorganisms present in the subsurface of contaminated DOE sites can significantly impact migration by directly reducing and immobilizing metals and radionuclides while degrading complex organic matter to low molecular weight organic compounds. These low molecular weight organic acids and alcohols can increase metal and radionuclide mobility by chelation (i.e., certain organic acids) or decrease mobility by stimulating respiratory metal reducing microorganisms. We demonstrated that fermentative organisms capable of affecting the fate of Cr6+, U6+ and trinitrotoluene can be isolated from organic-rich low level waste sites as well as from less organic rich subsurface environments. The mechanisms, pathways and extent of contaminant transformation depend on a variety of factors related to the type of organisms present, the aqueous chemistry as well as the geochemistry and mineralogy. This work provides observations and quantitative data across multiple scales that identify and predict the coupled effects of fermentative carbon and electron flow on the transport of radionuclides, heavy metals and organic contaminants in the subsurface; a primary concern of the DOE Environmental Remediation Science Division (ERSD) and Subsurface Geochemical Research (SBR) Program.« less

A reactive transport model for Marcellus shale weathering

NASA Astrophysics Data System (ADS)

Heidari, Peyman; Li, Li; Jin, Lixin; Williams, Jennifer Z.; Brantley, Susan L.

2017-11-01

Shale formations account for 25% of the land surface globally and contribute a large proportion of the natural gas used in the United States. One of the most productive shale-gas formations is the Marcellus, a black shale that is rich in organic matter and pyrite. As a first step toward understanding how Marcellus shale interacts with water in the surface or deep subsurface, we developed a reactive transport model to simulate shale weathering under ambient temperature and pressure conditions, constrained by soil and water chemistry data. The simulation was carried out for 10,000 years since deglaciation, assuming bedrock weathering and soil genesis began after the last glacial maximum. Results indicate weathering was initiated by pyrite dissolution for the first 1000 years, leading to low pH and enhanced dissolution of chlorite and precipitation of iron hydroxides. After pyrite depletion, chlorite dissolved slowly, primarily facilitated by the presence of CO2 and organic acids, forming vermiculite as a secondary mineral. A sensitivity analysis indicated that the most important controls on weathering include the presence of reactive gases (CO2 and O2), specific surface area, and flow velocity of infiltrating meteoric water. The soil chemistry and mineralogy data could not be reproduced without including the reactive gases. For example, pyrite remained in the soil even after 10,000 years if O2 was not continuously present in the soil column; likewise, chlorite remained abundant and porosity remained small if CO2 was not present in the soil gas. The field observations were only simulated successfully when the modeled specific surface areas of the reactive minerals were 1-3 orders of magnitude smaller than surface area values measured for powdered minerals. Small surface areas could be consistent with the lack of accessibility of some fluids to mineral surfaces due to surface coatings. In addition, some mineral surface is likely interacting only with equilibrated pore fluids. An increase in the water infiltration rate enhanced weathering by removing dissolution products and maintaining far-from-equilibrium conditions. We conclude from these observations that availability of reactive surface area and transport of H2O and gases are the most important factors affecting rates of Marcellus shale weathering of the in the shallow subsurface. This weathering study documents the utility of reactive transport modeling for complex subsurface processes. Such modelling could be extended to understand interactions between injected fluids and Marcellus shale gas reservoirs at higher temperature, pressure, and salinity conditions.

Modeling Subsurface Behavior at the System Level: Considerations and a Path Forward

NASA Astrophysics Data System (ADS)

Geesey, G.

2005-12-01

The subsurface is an obscure but essential resource to life on Earth. It is an important region for carbon production and sequestration, a source and reservoir for energy, minerals and metals and potable water. There is a growing need to better understand subsurface possesses that control the exploitation and security of these resources. Our best models often fail to predict these processes at the field scale because of limited understanding of 1) the processes and the controlling parameters, 2) how processes are coupled at the field scale 3) geological heterogeneities that control hydrological, geochemical and microbiological processes at the field scale and 4) lack of data sets to calibrate and validate numerical models. There is a need for experimental data obtained at scales larger than those obtained at the laboratory bench that take into account the influence of hydrodynamics, geochemical reactions including complexation and chelation/adsorption/precipitation/ion exchange/oxidation-reduction/colloid formation and dissolution, and reactions of microbial origin. Furthermore, the coupling of each of these processes and reactions needs to be evaluated experimentally at a scale that produces data that can be used to calibrate numerical models so that they accurately describe field scale system behavior. Establishing the relevant experimental scale for collection of data from coupled processes remains a challenge and will likely be process-dependent and involve iterations of experimentation and data collection at different intermediate scales until the models calibrated with the appropriate date sets achieve an acceptable level of performance. Assuming that the geophysicists will soon develop technologies to define geological heterogeneities over a wide range of scales in the subsurface, geochemists need to continue to develop techniques to remotely measure abiotic reactions, while geomicrobiologists need to continue their development of complementary technologies to remotely measure microbial community parameters that define their key functions at a scale that accurately reflects their role in large scale subsurface system behavior. The practical questions that geomicrobiologist must answer in the short term are: 1) What is known about the activities of the dominant microbial populations or those of their closest relatives? 2) Which of these activities is likely to dominate under in situ conditions? In the process of answering these questions, researchers will obtain answers to questions of a more fundamental nature such as 1) How deep does "active" life extend below the surface of the seafloor and terrestrial subsurface? 2) How are electrons exchanged between microbial cells and solid phase minerals? 3) What is the metabolic state and mechanism of survival of "inactive" life forms in the subsurface? 4) What can genomes of life forms trapped in geological material tell us about evolution of life that current methods cannot? The subsurface environment represents a challenging environment to understand and model. As the need to understand subsurface processes increases and the technologies to characterize them become available, modeling subsurface behavior will approach the level of sophistication of models used today to predict behavior of other large scale systems such as the oceans.

Summary of the Issues Regarding The Martian Subsurface Explorer

NASA Technical Reports Server (NTRS)

Eustes, A. W., III; Gertsch, L. S.; Lu, N.; Bridgford, E.; Tischler, A.; Stoner, M. S.; Wilcox, B. H.

2000-01-01

This is a summary of research work accomplished to date for the Jet Propulsion Laboratory by the Colorado School of Mines and the Michigan Technological University for the Martian Subsurface Explorer (SSX). The task involved a thorough review of the state of the art in drilling in the petroleum and mining industries in the following areas: 1) Drilling mechanics and energy requirements. 2) Sidewall friction in boreholes. 3) Rock property characteristics of basalt, permafrost, and ice. 4) Cuttings transport and recompaction of cuttings. and 5) Directional control at odd angle interfaces.

The thermal impact of subsurface building structures on urban groundwater resources - A paradigmatic example.

PubMed

Epting, Jannis; Scheidler, Stefan; Affolter, Annette; Borer, Paul; Mueller, Matthias H; Egli, Lukas; García-Gil, Alejandro; Huggenberger, Peter

2017-10-15

Shallow subsurface thermal regimes in urban areas are increasingly impacted by anthropogenic activities, which include infrastructure development like underground traffic lines as well as industrial and residential subsurface buildings. In combination with the progressive use of shallow geothermal energy systems, this results in the so-called subsurface urban heat island effect. This article emphasizes the importance of considering the thermal impact of subsurface structures, which commonly is underestimated due to missing information and of reliable subsurface temperature data. Based on synthetic heat-transport models different settings of the urban environment were investigated, including: (1) hydraulic gradients and conductivities, which result in different groundwater flow velocities; (2) aquifer properties like groundwater thickness to aquitard and depth to water table; and (3) constructional features, such as building depths and thermal properties of building structures. Our results demonstrate that with rising groundwater flow velocities, the heat-load from building structures increase, whereas down-gradient groundwater temperatures decrease. Thermal impacts on subsurface resources therefore have to be related to the permeability of aquifers and hydraulic boundary conditions. In regard to the urban settings of Basel, Switzerland, flow velocities of around 1 md -1 delineate a marker where either down-gradient temperature deviations or heat-loads into the subsurface are more relevant. Furthermore, no direct thermal influence on groundwater resources should be expected for aquifers with groundwater thicknesses larger 10m and when the distance of the building structure to the groundwater table is higher than around 10m. We demonstrate that measuring temperature changes down-gradient of subsurface structures is insufficient overall to assess thermal impacts, particularly in urban areas. Moreover, in areas which are densely urbanized, and where groundwater flow velocities are low, appropriate measures for assessing thermal impacts should specifically include a quantification of heat-loads into the subsurface which result in a more diffuse thermal contamination of urban groundwater resources. Copyright © 2017 Elsevier B.V. All rights reserved.

Validation, Proof-of-Concept, and Postaudit of the Groundwater Flow and Transport Model of the Project Shoal Area

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed Hassan

2004-09-01

The groundwater flow and radionuclide transport model characterizing the Shoal underground nuclear test has been accepted by the State of Nevada Division of Environmental Protection. According to the Federal Facility Agreement and Consent Order (FFACO) between DOE and the State of Nevada, the next steps in the closure process for the site are then model validation (or postaudit), the proof-of-concept, and the long-term monitoring stage. This report addresses the development of the validation strategy for the Shoal model, needed for preparing the subsurface Corrective Action Decision Document-Corrective Action Plan and the development of the proof-of-concept tools needed during the five-yearmore » monitoring/validation period. The approach builds on a previous model, but is adapted and modified to the site-specific conditions and challenges of the Shoal site.« less

Nanoscale Controls on CO2-water-rock Interactions in Saline Reservoirs

NASA Astrophysics Data System (ADS)

Deyoreo, J.; Depaolo, D. J.

2009-12-01

It is becoming increasingly widely recognized that geologic sequestration of CO2, when combined with economical means of capture, may be one of the most effective approaches to reducing net CO2 emissions to the atmosphere over the next century. Injection of CO2 into saline geologic formations involves forcing a buoyant, low-viscosity fluid into a more dense, higher viscosity fluid. The difference in wetting properties of the two fluids, their partial miscibility, the fact that CO2 and H2O form an acid, and the heterogeneity of geologic formations combine to make the flow and transport details fascinating but difficult to fully characterize and predict. A major question is whether the flow of CO2 into subsurface formations, the efficiency of pore space filling, and the trapping efficiency can be not only predicted but controlled over the decades of injection that might be associated with the life of a power plant. The major technological gaps to controlling and ultimately sequestering subsurface CO2 can be traced to far-from-equilibrum processes that originate at the molecular and nanoscale, but are expressed as complex emergent behavior at larger scales. Essential knowledge gaps involve the effects of nanoscale confinement on material properties, flow and chemical reactions, the effects of nanoparticles, mineral surface dynamics, and microbiota on mineral dissolution/precipitation and fluid flow, and the dynamics of fluid-fluid and fluid-mineral interfaces. To address these scientific and technical challenges, the Energy Frontier Research Center recently established, involving collaboration between LBNL, ORNL, MIT, UC Berkeley, UC Davis and LLNL, will attempt to bring new approaches to the study of nanoscale phenomena in fluid-rock systems to bear on the problem of CO2 behavior in saline formations. The stated goal is to use molecular, nanoscale, and pore-network scale approaches to control flow, dissolution, and precipitation in deep subsurface rock formations to achieve the efficient filling of pore space while maximizing solubility and mineral trapping and reducing potential leakage. Advanced knowledge of these small-scale processes is an important step toward developing a next-generation predictive capability for reactive transport of CO2-brine systems. The Center involves scientists with expertise in hydrology, geochemistry, materials science, mineralogy, chemistry, microbiology, geophysics, and reactive transport modeling and simulation. This presentation will describe the initial stages of some of the research, which in total involves the use of synchrotron light sources, neutron scattering methods, NanoSIMS, molecular dynamics simulations, thermochemistry, molecular biology, nanotechnology, laboratory scale experiments, and advanced computation applied to flow and reactive transport in heterogeneous porous media. The Center for Nanoscale Control of Geologic CO2 key personnel: Director - D. DePaolo, Co-Director - J. DeYoreo; Research Area Leads - K. Knauss (LBNL), G. Waychunas (LBNL), J. Banfield (UCB/LBNL), A Navrotsky (UC Davis), F.J. Ryerson (LLNL); G. Sposito (UCB/LBNL), T. Tokunaga (LBNL), D. Cole (ORNL), C. Steefel (LBNL), D. Rothman (MIT), S. Pride (LBNL).

Subsurface drainage erodes forested granitic terrane

Treesearch

Philip Durgin

1984-01-01

Abstract - Solution and landsliding, the dominant erosion processes in undisturbed forested mountainous watersheds, are both influenced by subsurface drainage. Biological processes that generate organic acids accelerate loss of dissolved solids by promoting the dissolution of primary minerals in granitic rock. These organic acids can also disperse the secondary...

Spot restoration for GPR image post-processing

DOEpatents

Paglieroni, David W; Beer, N. Reginald

2014-05-20

A method and system for detecting the presence of subsurface objects within a medium is provided. In some embodiments, the imaging and detection system operates in a multistatic mode to collect radar return signals generated by an array of transceiver antenna pairs that is positioned across the surface and that travels down the surface. The imaging and detection system pre-processes the return signal to suppress certain undesirable effects. The imaging and detection system then generates synthetic aperture radar images from real aperture radar images generated from the pre-processed return signal. The imaging and detection system then post-processes the synthetic aperture radar images to improve detection of subsurface objects. The imaging and detection system identifies peaks in the energy levels of the post-processed image frame, which indicates the presence of a subsurface object.

Rethinking hyporheic flow and transient storage to advance understanding of stream-catchment connections

USGS Publications Warehouse

Bencala, K.E.; Gooseff, M.N.; Kimball, B.A.

2011-01-01

Although surface water and groundwater are increasingly referred to as one resource, there remain environmental and ecosystem needs to study the 10 m to 1 km reach scale as one hydrologic system. Streams gain and lose water over a range of spatial and temporal scales. Large spatial scales (kilometers) have traditionally been recognized and studied as river-aquifer connections. Over the last 25 years hyporheic exchange flows (1-10 m) have been studied extensively. Often a transient storage model has been used to quantify the physical solute transport setting in which biogeochemical processes occur. At the longer 10 m to 1 km scale of stream reaches it is now clear that streams which gain water overall can coincidentally lose water to the subsurface. At this scale, the amounts of water transferred are not necessarily significant but the exchanges can, however, influence solute transport. The interpretation of seemingly straightforward questions about water, contaminant, and nutrient fluxes into and along a stream can be confounded by flow losses which are too small to be apparent in stream gauging and along flow paths too long to be detected in tracer experiments. We suggest basic hydrologic approaches, e.g., measurement of flow along the channel, surface and subsurface solute sampling, and routine measurements of the water table that, in our opinion, can be used to extend simple exchange concepts from the hyporheic exchange scale to a scale of stream-catchment connection. Copyright 2011 by the American Geophysical Union.

TOUGH3: A new efficient version of the TOUGH suite of multiphase flow and transport simulators

NASA Astrophysics Data System (ADS)

Jung, Yoojin; Pau, George Shu Heng; Finsterle, Stefan; Pollyea, Ryan M.

2017-11-01

The TOUGH suite of nonisothermal multiphase flow and transport simulators has been updated by various developers over many years to address a vast range of challenging subsurface problems. The increasing complexity of the simulated processes as well as the growing size of model domains that need to be handled call for an improvement in the simulator's computational robustness and efficiency. Moreover, modifications have been frequently introduced independently, resulting in multiple versions of TOUGH that (1) led to inconsistencies in feature implementation and usage, (2) made code maintenance and development inefficient, and (3) caused confusion to users and developers. TOUGH3-a new base version of TOUGH-addresses these issues. It consolidates both the serial (TOUGH2 V2.1) and parallel (TOUGH2-MP V2.0) implementations, enabling simulations to be performed on desktop computers and supercomputers using a single code. New PETSc parallel linear solvers are added to the existing serial solvers of TOUGH2 and the Aztec solver used in TOUGH2-MP. The PETSc solvers generally perform better than the Aztec solvers in parallel and the internal TOUGH3 linear solver in serial. TOUGH3 also incorporates many new features, addresses bugs, and improves the flexibility of data handling. Due to the improved capabilities and usability, TOUGH3 is more robust and efficient for solving tough and computationally demanding problems in diverse scientific and practical applications related to subsurface flow modeling.

Physical forcing of late summer chlorophyll a blooms in the oligotrophic eastern North Pacific

NASA Astrophysics Data System (ADS)

Toyoda, Takahiro; Okamoto, Suguru

2017-03-01

We investigated physical forcing of late summer chlorophyll a (chl a) blooms in the oligotrophic eastern North Pacific Ocean by using ocean reanalysis and satellite data. Relatively large chl a blooms as defined in this study occurred in August-October following sea surface temperature (SST) anomaly (SSTA) decreases, mixed layer deepening, and temperature and salinity increases at the bottom of the mixed layer. These physical conditions were apparently induced by the entrainment of subsurface water resulting from the destabilization of the surface layer caused by anomalous northward Ekman transport of subtropical waters of higher salinity. Salinity-normalized total alkalinity data provide supporting evidence for nutrient supply by the entrainment process. We next investigated the impact of including information about the entrainment on bloom identification. The results of analyses using reanalysis data and of those using only satellite data showed large SSTA decreases when the northward Ekman salinity transports were large, implying that the entrainment of subsurface water is well represented in both types of data. After surface-destabilizing conditions were established, relatively high surface chl a concentrations were observed. The use of SST information can further improve the detection of high chl a concentrations. Although the detection of high chl a concentrations would be enhanced by finer data resolution and the inclusion of biogeochemical parameters in the ocean reanalysis, our results obtained by using existing reanalysis data as well as recent satellite data are valuable for better understanding and prediction of lower trophic ecosystem variability.

Modeling Regolith Temperatures and Volatile Ice Processes (Invited)

NASA Astrophysics Data System (ADS)

Mellon, M. T.

2013-12-01

Surface and subsurface temperatures are an important tool for exploring the distribution and dynamics of volatile ices on and within planetary regoliths. I will review thermal-analysis approaches and recent applications in the studies of volatile ice processes. Numerical models of regolith temperatures allow us to examine the response of ices to periodic and secular changes in heat sources such as insolation. Used in conjunction with spatially and temporally distributed remotely-sensed temperatures, numerical models can: 1) constrain the stability and dynamics of volatile ices; 2) define the partitioning between phases of ice, gas, liquid, and adsorbate; and 3) in some instances be used to probe the distribution of ice hidden from view beneath the surface. The vapor pressure of volatile ices (such as water, carbon dioxide, and methane) depends exponentially on temperature. Small changes in temperature can result in transitions between stable phases. Cyclic temperatures and the propagation of thermal waves into the subsurface can produce a strong hysteresis in the population and partitioning of various phases (such as between ice, vapor, and adsorbate) and result in bulk transport. Condensation of ice will also have a pronounced effect on the thermal properties of otherwise loose particulate regolith. Cementing grains at their contacts through ice deposition will increase the thermal conductivity, and may enhance the stability of additional ice. Likewise sintering of grains within a predominantly icy regolith will increase the thermal conductivity. Subsurface layers that result from ice redistribution can be discriminated by remote sensing when combined with numerical modeling. Applications of these techniques include modeling of seasonal carbon dioxide frosts on Mars, predicting and interpreting the subsurface ice distribution on Mars and in Antarctica, and estimating the current depth of ice-rich permafrost on Mars. Additionally, understanding cold trapping ices in regions of the regolith of airless bodies, such as Mercury and the Moon, are aided by numerical modeling of regolith temperatures. Thermally driven sublimation of volatiles (water ice on Mars and more exotic species on icy moons in the outer solar system) can result in terrain degradation and collapse.

Wind-driven Sea-Ice Changes Intensify Subsurface Warm Water Intrusion into the West Antarctic Land Ice Front

NASA Astrophysics Data System (ADS)

Li, X.; Gille, S. T.; shang-Ping, X.; Xie, S. P.; Holland, D. M.; Holland, M. M.

2016-12-01

The climate change observed around Antarctica in recent decades is characterized by distinct zonally asymmetric patterns, with the strongest changes over West Antarctica. These changes are marked by strong land ice melting and sea ice redistribution around West Antarctica. This is associated with temperature and circulation anomalies in the ocean and atmosphere around the same area. In this study, we comprehensively examine the coherency between these changes using a combination of observations and numerical simulations. Results show that the atmospheric circulation changes distinctly drive the changes in ocean circulation and sea ice distribution. In addition, the atmospheric circulation induced sea ice changes play an important role in lifting the subsurface ocean temperature and salinity around the West Antarctica. During recent decades, the Amundsen Sea Low (ASL) has deepened, especially in austral autumn and winter. This deepened ASL has intensified the offshore wind near the coastal regions of the Ross Sea. Driven by these atmospheric changes, more sea ice has formed near West Antarctica in winter. In contrast, more sea ice melts during the summer. This strengthened sea ice seasonality has been observed and successfully reproduced in the model simulation. The wind-driven sea ice changes causes a surface freshening over the Ross and Amundsen Seas, with a subsurface salinity increase over the Ross Sea. The additional fresh/salt water fluxes thus further change the vertical distribution of salinity and strengthen the stratification in the Ross and Amundsen Seas. As a result of the above ice-ocean process, the mixed-layer depth around the Ross and Amundsen Seas shallows. By weakening the vertical heat transport near the surface layer, and inducing an upward movement of the circumpolar deep water (CDW), this process freshened and cooled the surface layer, while the salinity and temperature in the sub-surface ocean are increased, extending from 150 meters to >700 meters. Around the Amundsen Sea, warm water touches the continent, which could potentially contribute to the accelerated land ice melting over this area.

Sulfate deposition in subsurface regolith in Gusev crater, Mars

USGS Publications Warehouse

Wang, A.; Haskin, L.A.; Squyres, S. W.; Jolliff, B.L.; Crumpler, L.; Gellert, Ralf; Schroder, C.; Herkenhoff, K.; Hurowitz, J.; Tosca, N.J.; Farrand, W. H.; Anderson, R.; Knudson, A.T.

2006-01-01

Excavating into the shallow Martian subsurface has the potential to expose stratigraphic layers and mature regolith, which may hold a record of more ancient aqueous interactions than those expected under current Martian surface conditions. During the Spirit rover's exploration of Gusev crater, rover wheels were used to dig three trenches into the subsurface regolith down to 6-11 cm depth: Road Cut, the Big Hole, and The Boroughs. A high oxidation state of Fe and high concentrations of Mg, S, Cl, and Br were found in the subsurface regolith within the two trenches on the plains, between the Bonneville crater and the foot of Columbia Hills. Data analyses on the basis of geochemistry and mineralogy observations suggest the deposition of sulfate minerals within the subsurface regolith, mainly Mg-sulfates accompanied by minor Ca-sulfates and perhaps Fe-sulfates. An increase of Fe2O3, an excess of SiO2, and a minor decrease in the olivine proportion relative to surface materials are also inferred. Three hypotheses are proposed to explain the geochemical trends observed in trenches: (1) multiple episodes of acidic fluid infiltration, accompanied by in situ interaction with igneous minerals and salt deposition; (2) an open hydrologic system characterized by ion transportation in the fluid, subsequent evaporation of the fluid, and salt deposition; and (3) emplacement and mixing of impact ejecta of variable composition. While all three may have plausibly contributed to the current state of the subsurface regolith, the geochemical data are most consistent with ion transportation by fluids and salt deposition as a result of open-system hydrologic behavior. Although sulfates make up >20 wt.% of the regolith in the wall of The Boroughs trench, a higher hydrated sulfate than kieserite within The Boroughs or a greater abundance of sulfates elsewhere than is seen in The Boroughs wall regolith would be needed to hold the structural water indicated by the water-equivalent hydrogen concentration observed by the Gamma-Ray Spectrometer on Odyssey in the Gusev region. Copyright 2006 by the American Geophysical Union.