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Sample records for media unsaturated zone

  1. A model for the effective diffusion of gas or the vapor phase in a fractured media unsaturated zone driven by periodic atmospheric pressure fluctuations

    SciTech Connect

    Vold, E.L.

    1997-03-01

    There is evidence for migration of tritiated water vapor through the tuff in the unsaturated zone from the buried disposal shafts located on a narrow mesa top at Area G, Los Alamos, NM. Field data are consistent with an effective in-situ vapor phase diffusion coefficient of 1.5x10{sup {minus}3} m{sup s}/s, or a factor of 60 greater than the binary diffusion coefficient for water vapor in air. A model is derived to explain this observation of anomolously large diffusion, which relates an effective vapor or gas phase diffusion coefficient in the fractured porous media to the subsurface propagation of atmospheric pressure fluctuations (barometric pumping). The near surface (unattenuated) diffusion coefficient is independent of mode period under the simplified assumptions of a complete {open_quote}mixing mechanism{close_quote} for the effective diffusion process. The unattenuated effective diffusion driven by this barometric pumping is proportional to an average media permeability times the sum of the square of pressure mode amplitudes, while the attenuation length is proportional to the squarer root of the product of permeability times mode period. There is evidence that the permeability needed to evaluate the pressure attenuation length is the in-situ value, approximately that of the matrix. The diffusion which results using Area G parameter values is negligible in the matrix but becomes large at the effective permeability of the fractured tuff matrix. The effective diffusion coefficient predicted by this model, due to pressure fluctuations and the observed fracture characteristics, is in good agreement with the observed in-situ diffusion coefficient for tritium field measurements. It is concluded that barometric pumping in combination with the enhanced permeability of the fractured media is a likely candidate to account for the observed in-field migration of vapor in the near surface unsaturated zone at Area G.

  2. Do Karstic Unsaturated Zones Have the Fastest Preferential Flow?

    NASA Astrophysics Data System (ADS)

    Nimmo, J. R.; Perkins, K. S.

    2013-12-01

    There is strong evidence that unsaturated-zone travel times for preferential flow, unlike those for diffuse flow, mostly fall within a relatively small range, even for a wide variety of media and conditions [Nimmo, 2007, Water Resources Research]. We have calculated travel times for preferential flow observations published in the last seven years, finding a range of travel velocities with a greater maximum than was previously recognized. The instances of faster transport, however, are predominantly for karst or other materials in which water flow may strongly influence the creation and development of preferential flow paths. These findings motivate a hypothesis: in media where the matrix is soluble, erodible, or otherwise vulnerable to enlargement by flowing water, this flow acts to reduce flow impediments within a macropore network. This might be thought of as a sculpting process in which water carves its conduit into a smoother, larger, less constrictive shape, as discussed in connection with soil pipes [Jones, 2010, Hydrological Processes]. Known developmental processes of karst and epikarst are consistent with this hypothesis. Its acceptance would open doors to expanded use of optimality and thermodynamic principles to understand and predict preferential flow. It also could lead to new modes of hydraulic characterization of subsurface media with regard to unsaturated flow, which are much needed as the difficulty of measuring hydraulic properties of the unsaturated zone is a major barrier to the advance of hydrologic science. In practical terms, a new guideline may be justified: in unsaturated karst or other materials in which flowing water may enhance flowpaths, preferential transport rates in general may be several times faster than through media without such pore-developmental processes.

  3. NaturAnalogs for the Unsaturated Zone

    SciTech Connect

    A. Simmons; A. Unger; M. Murrell

    2000-03-08

    The purpose of this Analysis/Model Report (AMR) is to document natural and anthropogenic (human-induced) analog sites and processes that are applicable to flow and transport processes expected to occur at the potential Yucca Mountain repository in order to build increased confidence in modeling processes of Unsaturated Zone (UZ) flow and transport. This AMR was prepared in accordance with ''AMR Development Plan for U0135, Natural Analogs for the UZ'' (CRWMS 1999a). Knowledge from analog sites and processes is used as corroborating information to test and build confidence in flow and transport models of Yucca Mountain, Nevada. This AMR supports the Unsaturated Zone (UZ) Flow and Transport Process Model Report (PMR) and the Yucca Mountain Site Description. The objectives of this AMR are to test and build confidence in the representation of UZ processes in numerical models utilized in the UZ Flow and Transport Model. This is accomplished by: (1) applying data from Boxy Canyon, Idaho in simulations of UZ flow using the same methodologies incorporated in the Yucca Mountain UZ Flow and Transport Model to assess the fracture-matrix interaction conceptual model; (2) Providing a preliminary basis for analysis of radionuclide transport at Pena Blanca, Mexico as an analog of radionuclide transport at Yucca Mountain; and (3) Synthesizing existing information from natural analog studies to provide corroborating evidence for representation of ambient and thermally coupled UZ flow and transport processes in the UZ Model.

  4. Gas transport in unsaturated porous media: the adequacy of Fick's law

    USGS Publications Warehouse

    Thorstenson, D.C.; Pollock, D.W.

    1989-01-01

    The increasing use of natural unsaturated zones as repositories for landfills and disposal sites for hazardous wastes (chemical and radioactive) requires a greater understanding of transport processes in the unsaturated zone. For volatile constituents an important potential transport mechanism is gaseous diffusion. Diffusion, however, cannot be treated as an independent isolated transport mechanism. A complete understanding of multicomponent gas transport in porous media (unsaturated zones) requires a knowledge of Knudsen transport, the molecular and nonequimolar components of diffusive flux, and viscous (pressure driven) flux. This review presents a brief discussion of the underlying principles and interrelationships among each of the above flux mechanisms. -from Authors

  5. The geometry of nonwetting liquids in the unsaturated zone

    SciTech Connect

    Hartz, M.J.; Overcamp, T.J.

    1996-09-01

    In hydrophilic aquifer material, gasoline, immiscible solvents, and similar nonaqueous phase liquids (NAPL) form a separate nonwetting phase. If such a nonwetting liquid is spilled onto soil, it will percolate into the soil and migrate downward and laterally under the influence of gravity and capillary forces. As the nonwetting liquid drains from a portion of soil, some of this liquid is retained by capillary forces. Although current models predict that the retained nonwetting liquid is immobile a growing body of evidence indicates that it may be displaced by percolating water. A theory is developed to describe the geometry of nonwetting or nonaqueous phase liquids in moist unsaturated media. This theory predicts that liquids with positive values of the classical two-dimensional spreading coefficient form pendular rings. Liquids with negative values form pendular rings in regions of high-water tension or in regions of relatively high concentration of the nonwetting fluid, but they form insular lenses in regions of low-water tension or regions of low concentration of the nonwetting fluid. A three-dimensional spreading coefficient was developed to predict this behavior. Infiltrating water can cause transitions by breaking the pendular rings of nonwetting liquids in the unsaturated zone, and forming larger blobs as these rings coalesce. These blobs may drain downward due to gravity. These conditions may contribute to the mobility of nonwetting liquids due to percolation of water through the unsaturated zone.

  6. Unsaturated Zone and Saturated Zone Transport Properties (U0100)

    SciTech Connect

    J. Conca

    2000-12-20

    This Analysis/Model Report (AMR) summarizes transport properties for the lower unsaturated zone hydrogeologic units and the saturated zone at Yucca Mountain and provides a summary of data from the Busted Butte Unsaturated Zone Transport Test (UZTT). The purpose of this report is to summarize the sorption and transport knowledge relevant to flow and transport in the units below Yucca Mountain and to provide backup documentation for the sorption parameters decided upon for each rock type. Because of the complexity of processes such as sorption, and because of the lack of direct data for many conditions that may be relevant for Yucca Mountain, data from systems outside of Yucca Mountain are also included. The data reported in this AMR will be used in Total System Performance Assessment (TSPA) calculations and as general scientific support for various Process Model Reports (PMRs) requiring knowledge of the transport properties of different materials. This report provides, but is not limited to, sorption coefficients and other relevant thermodynamic and transport properties for the radioisotopes of concern, especially neptunium (Np), plutonium (Pu), Uranium (U), technetium (Tc), iodine (I), and selenium (Se). The unsaturated-zone (UZ) transport properties in the vitric Calico Hills (CHv) are discussed, as are colloidal transport data based on the Busted Butte UZTT, the saturated tuff, and alluvium. These values were determined through expert elicitation, direct measurements, and data analysis. The transport parameters include information on interactions of the fractures and matrix. In addition, core matrix permeability data from the Busted Butte UZTT are summarized by both percent alteration and dispersion.

  7. IDENTIFICATION AND COMPILATION OF UNSATURATED/VADOSE ZONE MODELS

    EPA Science Inventory

    The present report contains the result of research and information processing activities supporting evaluation of the capabilities of various unsaturated zone flow and transport models in predicting the movement of hazardous chemicals through soils to ground water. t provides an ...

  8. Unsaturated Zone Flow Patterns and Analysis

    SciTech Connect

    C. Ahlers

    2001-10-17

    This Analysis/Model Report (AMR) documents the development of an expected-case model for unsaturated zone (UZ) flow and transport that will be described in terms of the representativeness of models of the natural system. The expected-case model will provide an evaluation of the effectiveness of the natural barriers, assess the impact of conservatism in the Total System Performance Assessment (TSPA), and support the development of further models and analyses for public confidence building. The present models used in ''Total System Performance Assessment for the Site Recommendation'' (Civilian Radioactive Waste Management System Management and Operating Contractor (CRWMS M&O) 2000 [1532461]) underestimate the natural-barrier performance because of conservative assumptions and parameters and do not adequately address uncertainty and alternative models. The development of an expected case model for the UZ natural barrier addresses issues regarding flow-pattern analysis and modeling that had previously been treated conservatively. This is in line with the Repository Safety Strategy (RSS) philosophy of treating conservatively those aspects of the UZ flow and transport system that are not important for achieving regulatory dose (CRWMS M&O 2000 [153246], Section 1.1.1). The development of an expected case model for the UZ also provides defense-in-depth in areas requiring further analysis of uncertainty and alternative models. In general, the value of the conservative case is to provide a more easily defensible TSPA for behavior of UZ flow and transport processes at Yucca Mountain. This AMR has been prepared in accordance with the ''Technical Work Plan for Unsaturated Zone (UZ) Flow and Transport Process Model Report'' (Bechtel SAIC Company (BSC) 2001 [155051], Section 1.3 - Work Package 4301213UMG). The work scope is to examine the data and current models of flow and transport in the Yucca Mountain UZ to identify models and analyses where conservatism may be reduced and

  9. Unsaturated zone 14CO2: implications for groundwater dating

    NASA Astrophysics Data System (ADS)

    Wood, C.; Cook, P. G.; Harrington, G. A.; Meredith, K.; Kipfer, R.

    2013-12-01

    Quantitative interpretation of the carbon-14 activity (14C) of dissolved inorganic carbon (DIC) in groundwater requires an understanding of the various chemical and physical processes that can vary the initial 14C activity from that of the original atmospheric source (carbon dioxide, CO2). Such processes include radioactive decay, carbonate mineral dissolution, isotope exchange, decay of organic matter and molecular diffusion. Many geochemical correction models exist to account for some of these processes (e.g., Fontes and Garnier, 1979). However in most existing correction schemes, it is assumed that the 14C activity of CO2 in the unsaturated zone is in equilibrium with the atmosphere (i.e., 14C:12C is the same as the atmospheric ratio). This assumption is rarely tested and in several cases has been found to be inappropriate (eg. Bacon and Keller, 1998; Walvoord et al., 2005). Not accounting for the influence of unsaturated zone processes on 14C may lead to problems in determining residence time and estimating fluxes from measured 14C data in groundwater. In this study we examined carbon isotope processes in deep unsaturated zone profiles (up to 30m in depth) in arid central Australia. At five sites, multi-level samples of unsaturated zone gas and groundwater were collected for 14C analysis. Chlorofluorocarbon (CFC-11 and CFC-12) samples were also collected in unsaturated zone gas. At all sites we observed a decrease in the 14C activity of unsaturated zone gas with depth, from approximately 107 pmC near the ground surface to 50 - 80 pmC immediately above the water table. The measured 14C data was reproduced in a one-dimensional model using Hydrus, with CFC concentrations used to help constrain the gas transport parameters. Modelling showed that the decrease in 14C could be explained by CO2 production from different sources at different depths in the unsaturated zone (e.g. plant root respiration at shallower depths, oxidation of dead organic matter at greater

  10. Upscaling of Constitutive Relations I Unsaturated Heterogeneous Porous Media

    SciTech Connect

    H. H. Liu; G. S. Bodvarsson

    2001-05-31

    When numerical model are used for modeling field scale flow and transport processes in the subsurface, the problem of ''upscaling'' arises. Typical scales, corresponding to spatial resolutions of subsurface heterogeneity in numerical models, are generally much larger than the measurement scale of the parameters and physical processes involved. The upscaling problems is, then, one of assigning parameters to gridblock scale based on parameter values measured on small scales. The focus of this study is to develop an approach to determine large-scale (upscaled) constitutive relations (relationships among relative permeability, capillary pressure and saturation) from small-scale measurements for porous media for a range of air entry values that are typical for the tuff matrix in the unsaturated zone of Yucca Mountain. For porous media with large air entry values, capillary forces play a key role in determining spatial water distribution at large-scales. Therefore, a relatively uniform capillary pressure approximately exists even for a large gridblock scale under steady state flow conditions. Based on these reasoning, we developed formulations that relate upscaled constitutive relations to ones measured at core-scale. Numerical experiments with stochastically generated heterogeneous porous media were used to evaluate the upscaling formulations.

  11. Modeling Unsaturated Flow and Transport using Zones: Aliasing Errors

    NASA Astrophysics Data System (ADS)

    Schafer, A. L.; Holt, R. M.

    2001-12-01

    It is difficult and costly to accurately determine the spatial statistics of unsaturated hydraulic properties, whereas it is often easier to define hydraulic property zones. When heterogeneous hydraulic property fields are subdivided into zones, however, flow and transport predictions show aliasing errors that alter predicted concentrations and breakthrough curves. The amount of error varies with the number of zones, the character of the heterogeneity, and boundary and initial conditions. The objective of this work is to determine the number of zones required to preserve critical transport behavior during numerical simulation of flow and transport. For this exercise, we consider unsaturated flow and non-reactive transport only. We assume that Richard?s Equation is valid and that the Gardner-Russo parametric model exactly describes unsaturated constitutive relationships. Correlated random parameter fields are generated and unsaturated flow and transport through these fields is simulated. The fields are then zoned using quantiles (0.25, 0.1, 0.05, and 0.025), appropriate zonal averages are determined, and flow and transport is simulated through the zoned fields. Aliasing errors are assessed by comparing the first, second and third moments of concentration for the full and zoned fields. The number of zones is varied to elucidate the character of aliasing error. The style of heterogeneity is varied to reflect geologically relevant end members (statistically isotropic vs. perfectly layered fields). Simulations are repeated under unit gradient conditions at mean tensions of 10, 100, and 1000 cm. Aliasing errors will tend to be smallest in layered systems with flow perpendicular to layering, because zonal averaging does not obscure fast paths. In statistically isotropic systems, fast paths are reduced as the coarseness of the zones increases. At higher tensions, finer zones are required to preserve transport behavior.

  12. Unsaturated zone flow modeling for GWTT-95

    SciTech Connect

    Ho, C.K.; Altman, S.J.; McKenna, S.A.; Arnold, B.W.

    1995-12-31

    In accordance with the Nuclear Regulatory Commission regulation regarding groundwater travel times at geologic repositories, various models of unsaturated flow in fractured tuff have been developed and implemented to assess groundwater travel times at the potential repository at Yucca Mountain, Nevada. Kaplan used one-dimensional models to describe the uncertainty and sensitivity of travel times to various processes at Yucca Mountain. Robey and Arnold et al. used a two-dimensional equivalent continuum model (ECM) with inter- and intra-unit heterogeneity in an attempt to assess fast-flow paths through the unsaturated, fractured tuff at Yucca Mountain (GWTT-94). However, significant flow through the fractures in previous models was not simulated due to the characteristics of the ECM, which requires the matrix to be nearly saturated before flow through the fractures is initiated. In the current study (GWTT-95), four two-dimensional cross-sections at Yucca Mountain are simulated using both the ECM and dual-permeability (DK) models. The properties of both the fracture and matrix domains are geostatistically simulated, yielding completely heterogeneous continua. Then, simulations of flow through the four cross-sections are performed using spatially nonuniform infiltration boundary conditions. Steady-state groundwater travel times from the potential repository to the water table are calculated.

  13. Chaotic dynamics in flow through unsaturated fractured media

    NASA Astrophysics Data System (ADS)

    Faybishenko, Boris

    Predictions of flow and transport within fractured rock in the vadose zone cannot be made without first characterizing the physics of unstable flow phenomena in unsaturated fractures. This paper introduces a new approach for studying complex flow processes in heterogeneous fractured media, using the methods of nonlinear dynamics and chaos--in particular reconstructing the system dynamics and calculating chaotic diagnostic parameters from time-series data. To demonstrate the application of chaotic analysis, this author analyzed the time-series pressure fluctuations from two water-air flow experiments conducted by Persoff and Pruess [Water Resour. Res. 31 (1995) 1175] in replicas of rough-walled rock fractures under controlled boundary conditions. This analysis showed that chaotic flow in fractures creates relaxational oscillations of liquid, gas, and capillary pressures. These pressure oscillations were used to calculate the diagnostic parameters of deterministic chaos, including correlation time, global embedding dimension, local embedding dimension, Lyapunov dimension, Lyapunov exponents, and correlation dimension. The results of the Persoff-Pruess experiments were then compared with the chaotic analysis of laboratory dripping-water experiments in fracture models and field-infiltration experiments in fractured basalt. This comparison allowed us to conjecture that intrinsic fracture flow and dripping, as well as extrinsic water dripping (from a fracture) subjected to a capillary-barrier effect, are deterministic-chaotic processes with a certain random component. The unsaturated fractured rock is a dynamic system that exhibits chaotic behavior because the flow processes are nonlinear, dissipative, and sensitive to initial conditions, with chaotic fluctuations generated by intrinsic properties of the system, not random external factors. Identifying a system as deterministically chaotic is important for developing appropriate short- and long-term prediction models

  14. Hydraulic properties of adsorbed water films in unsaturated porous media

    SciTech Connect

    Tokunaga, Tetsu K.

    2009-03-01

    Adsorbed water films strongly influence residual water saturations and hydraulic conductivities in porous media at low saturations. Hydraulic properties of adsorbed water films in unsaturated porous media were investigated through combining Langmuir's film model with scaling analysis, without use of any adjustable parameters. Diffuse double layer influences are predicted to be important through the strong dependence of adsorbed water film thickness (f) on matric potential ({Psi}) and ion charge (z). Film thickness, film velocity, and unsaturated hydraulic conductivity are predicted to vary with z{sup -1}, z{sup -2}, and z{sup -3}, respectively. In monodisperse granular media, the characteristic grain size ({lambda}) controls film hydraulics through {lambda}{sup -1} scaling of (1) the perimeter length per unit cross sectional area over which films occur, (2) the critical matric potential ({Psi}{sub c}) below which films control flow, and (3) the magnitude of the unsaturated hydraulic conductivity when {Psi} < {Psi}{sub c}. While it is recognized that finer textured sediments have higher unsaturated hydraulic conductivities than coarser sands at intermediate {Psi}, the {lambda}{sup -1} scaling of hydraulic conductivity predicted here extends this understanding to very low saturations where all pores are drained. Extremely low unsaturated hydraulic conductivities are predicted under adsorbed film-controlled conditions (generally < 0.1 mm y{sup -1}). On flat surfaces, the film hydraulic diffusivity is shown to be constant (invariant with respect to {Psi}).

  15. 40 CFR 264.278 - Unsaturated zone monitoring.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... or operator must monitor the soil and soil-pore liquid to determine whether hazardous constituents... unsaturated zone monitoring system that includes soil monitoring using soil cores and soil-pore liquid... the quality of background soil-pore liquid quality and the chemical make-up of soil that has not...

  16. 40 CFR 264.278 - Unsaturated zone monitoring.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... or operator must monitor the soil and soil-pore liquid to determine whether hazardous constituents... unsaturated zone monitoring system that includes soil monitoring using soil cores and soil-pore liquid... the quality of background soil-pore liquid quality and the chemical make-up of soil that has not...

  17. BIODEGRADATION OF HYDROCARBON VAPORS IN THE UNSATURATED ZONE

    EPA Science Inventory

    The time-averaged concentration of hydrocarbon and oxygen vapors were measured in the unsaturated zone above the residually contaminated capillary fringe at the U.S. Coast Guard Air Station in Traverse City, Michigan. Total hydrocarbon and oxygen vapor concentrations were observe...

  18. Comparison of different filter methods for data assimilation in the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Lange, Natascha; Berkhahn, Simon; Erdal, Daniel; Neuweiler, Insa

    2016-04-01

    The unsaturated zone is an important compartment, which plays a role for the division of terrestrial water fluxes into surface runoff, groundwater recharge and evapotranspiration. For data assimilation in coupled systems it is therefore important to have a good representation of the unsaturated zone in the model. Flow processes in the unsaturated zone have all the typical features of flow in porous media: Processes can have long memory and as observations are scarce, hydraulic model parameters cannot be determined easily. However, they are important for the quality of model predictions. On top of that, the established flow models are highly non-linear. For these reasons, the use of the popular Ensemble Kalman filter as a data assimilation method to estimate state and parameters in unsaturated zone models could be questioned. With respect to the long process memory in the subsurface, it has been suggested that iterative filters and smoothers may be more suitable for parameter estimation in unsaturated media. We test the performance of different iterative filters and smoothers for data assimilation with a focus on parameter updates in the unsaturated zone. In particular we compare the Iterative Ensemble Kalman Filter and Smoother as introduced by Bocquet and Sakov (2013) as well as the Confirming Ensemble Kalman Filter and the modified Restart Ensemble Kalman Filter proposed by Song et al. (2014) to the original Ensemble Kalman Filter (Evensen, 2009). This is done with simple test cases generated numerically. We consider also test examples with layering structure, as a layering structure is often found in natural soils. We assume that observations are water content, obtained from TDR probes or other observation methods sampling relatively small volumes. Particularly in larger data assimilation frameworks, a reasonable balance between computational effort and quality of results has to be found. Therefore, we compare computational costs of the different methods as well

  19. Effects of unsaturated zone on ground-water mounding

    USGS Publications Warehouse

    Sumner, D.M.; Rolston, D.E.; Marino, M.A.

    1999-01-01

    The design of infiltration basins used to dispose of treated wastewater or for aquifer recharge often requires estimation of ground-water mounding beneath the basin. However, the effect that the unsaturated zone has on water-table response to basin infiltration often has been overlooked in this estimation. A comparison was made between two methods used to estimate ground-water mounding-an analytical approach that is limited to the saturated zone and a numerical approach that incorporates both the saturated and the unsaturated zones. Results indicate that the error that is introduced by a method that ignores the effects of the unsaturated zone on ground-water mounding increases as the basin-loading period is shortened; as the depth to the water table increases, with increasing subsurface anisotropy; and with the inclusion of fine-textured strata. Additionally, such a method cannot accommodate the dynamic nature of basin infiltration, the finite transmission time of the infiltration front to the water table, or the interception of the basin floor by the capillary fringe.The design of infiltration basins used to dispose of treated wastewater or for aquifer recharge often requires estimation of ground-water mounding beneath the basin. However, the effect that the unsaturated zone has on water-table response to basin infiltration often has been overlooked in this estimation. A comparison was made between two methods used to estimate ground-water mounding - an analytical approach that is limited to the saturated zone and a numerical approach that incorporates both the saturated and the unsaturated zones. Results indicate that the error that is introduced by a method that ignores the effects of the unsaturated zone on ground-water mounding increases as the basin-loading period is shortened; as the depth to the water table increases, with increasing subsurface anisotropy; and with the inclusion of fine-textured strata. Additionally, such a method cannot accommodate the

  20. Colloid Bound Transport of Contaminats In The Unsaturated Zone

    NASA Astrophysics Data System (ADS)

    Hofmann, T.; Christ, A.

    Colloids can play a major role in the relocation of contaminants in the unsaturated zone. The amount of colloid driven transport is defined by soil chemistry, soil water chemistry and water flow velocity as well as colloid composition and formation. In a current research project we investigate the filtration and mobilization of colloids in unsaturated column studies. We use different soil types, chosen by a wide range of mean grain size and heterogeneity. Particle tracers are polystyrene solids with a de- fined negative surface charge and defined size from 50 nm to 10 µm. In addition, we use natural colloids extracted from a wide range of contaminated and uncontaminated land. Experimental conditions are exactly controlled throughout all the time. We alter mainly flow velocity ionic strength in order to study the filtration behaviour of the soils. In addition, Pyrene and Lead are are used as model contaminants. First results show the colloids are not retarded in many coarse structured soil types. Preferential colloid flow shows a major impact in breakthrough behaviour. Colloid bound lead is relocated significant through the unsaturated zone, whereas non colloid bound lead species are strongly retarded. In the presentation we will show results of contami- nant processes and present new results on the filtration behaviour of colloids in the unsaturated zone depending on flow velocity, soil type and colloid size.

  1. Heat and mass transfer in unsaturated porous media. Final report

    SciTech Connect

    Childs, S.W.; Malstaff, G.

    1982-02-01

    A preliminary study of heat and water transport in unsaturated porous media is reported. The project provides background information regarding the feasibility of seasonal thermal energy storage in unconfined aquifers. A parametric analysis of the factors of importance, and an annotated bibliography of research findings pertinent to unconfined aquifer thermal energy storage (ATES) are presented. This analysis shows that heat and mass transfer of water vapor assume dominant importance in unsaturated porous media at elevated temperature. Although water vapor fluxes are seldom as large as saturated medium liquid water fluxes, they are important under unsaturated conditions. The major heat transport mechanism for unsaturated porous media at temperatures from 50 to 90/sup 0/C is latent heat flux. The mechanism is nonexistent under saturated conditions but may well control design of unconfined aquifer storage systems. The parametric analysis treats detailed physical phenomena which occur in the flow systems study and demonstrates the temperature and moisture dependence of the transport coefficients of importance. The question of design of an unconfined ATES site is also addressed by considering the effects of aquifer temperature, depth to water table, porous medium flow properties, and surface boundary conditions. Recommendations are made for continuation of this project in its second phase. Both scientific and engineering goals are considered and alternatives are presented.

  2. Transport of Polycyclic Aromatic Hydrocarbons in Unsaturated Porous Media

    NASA Astrophysics Data System (ADS)

    Chahal, Maninder; Flury, Markus

    2016-04-01

    Polycyclic aromatic hydrocarbons (PAHs) are complex organic molecules containing 2 or more fused benzene rings. Being hydrophobic and non-polar, PAHs tend to partition to the organic matter in the soil from bulk aqueous phase. Though transport of these contaminants has been well studied in saturated environment, interactive mechanisms of these fluorescent compounds in unsaturated (identified by presence of air-water interface) porous media is still not well understood. We studied is the transport of fluoranthene in unsaturated porous media as facilitated by moving air-water interfaces. Confocal microscopy was used to visualize the interactions of fluoranthene particles in a glass channel packed with quartz glass beads. The packed glass channel was used to mimic a porous media and effects of an advancing and receding capillary fringe on the detachment of fluoranthene.

  3. Liquid flow and distribution in unsaturated porous media

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan

    2004-01-01

    Flow and transport in permeable or porous media and microchannels occurs in a variety of situations in micro- and reduced-gravity environments, many of them associated with environmental control and life support systems. While the role of gravity is limited, due to the typically small size scales associated permeable media, gravity, at the very least, affects the overall disposition of fluid in a macroscopic system. This presentation will discuss examples where the absence of gravity affects flow and phase distribution in selected examples of unsaturated flow and transport of heat and mass in porous media and microchannels that are pertinent to spacecraft systems.

  4. Volatile organic compounds in the unsaturated zone from radioactive wastes.

    PubMed

    Baker, Ronald J; Andraski, Brian J; Stonestrom, David A; Luo, Wentai

    2012-01-01

    Volatile organic compounds (VOCs) are often comingled with low-level radioactive wastes (LLRW), but little is known about subsurface VOC emanations from LLRW landfills. The current study systematically quantified VOCs associated with LLRW over an 11-yr period at the USGS Amargosa Desert Research Site (ADRS) in southwestern Nevada. Unsaturated-zone gas samples of VOCs were collected by adsorption on resin cartridges and analyzed by thermal desorption and GC/MS. Sixty of 87 VOC method analytes were detected in the 110-m-thick unsaturated zone surrounding a LLRW disposal facility. Chlorofluorocarbons (CFCs) were detected in 100% of samples collected. Chlorofluorocarbons are powerful greenhouse gases, deplete stratospheric ozone, and are likely released from LLRW facilities worldwide. Soil-gas samples collected from a depth of 24 m and a horizontal distance 100 m south of the nearest waste-disposal trench contained >60,000 ppbv total VOCs, including >37,000 ppbv CFCs. Extensive sampling in the shallow unsaturated zone (0-2 m deep) identified areas where total VOC concentrations exceeded 5000 ppbv at the 1.5-m depth. Volatile organic compound concentrations exceeded background levels up to 300 m from the facility. Maximum vertical diffusive fluxes of total VOCs were estimated to be 1 g m yr. Volatile organic compound distributions were similar but not identical to those previously determined for tritium and elemental mercury. To our knowledge, this study is the first to characterize the unsaturated zone distribution of VOCs emanating from a LLRW landfill. Our results may help explain anomalous transport of radionuclides at the ADRS and elsewhere. PMID:22751077

  5. Artificial recharge through a thick, heterogeneous unsaturated zone.

    PubMed

    Izbicki, John A; Flint, Alan L; Stamos, Christina L

    2008-01-01

    Thick, heterogeneous unsaturated zones away from large streams in desert areas have not previously been considered suitable for artificial recharge from ponds. To test the potential for recharge in these settings, 1.3 x 10(6) m(3) of water was infiltrated through a 0.36-ha pond along Oro Grande Wash near Victorville, California, between October 2002 and January 2006. The pond overlies a regional pumping depression 117 m below land surface and is located where thickness and permeability of unsaturated deposits allowed infiltration and saturated alluvial deposits were sufficiently permeable to allow recovery of water. Because large changes in water levels caused by nearby pumping would obscure arrival of water at the water table, downward movement of water was measured using sensors in the unsaturated zone. The downward rate of water movement was initially as high as 6 m/d and decreased with depth to 0.07 m/d; the initial time to reach the water table was 3 years. After the unsaturated zone was wetted, water reached the water table in 1 year. Soluble salts and nitrate moved readily with the infiltrated water, whereas arsenic and chromium were less mobile. Numerical simulations done using the computer program TOUGH2 duplicated the downward rate of water movement, accumulation of water on perched zones, and its arrival at the water table. Assuming 10 x 10(6) m(3) of recharge annually for 20 years, a regional ground water flow model predicted water level rises of 30 m beneath the ponds, and rises exceeding 3 m in most wells serving the nearby urban area. PMID:18194322

  6. Artificial recharge through a thick, heterogeneous unsaturated zone

    USGS Publications Warehouse

    Izbicki, J.A.; Flint, A.L.; Stamos, C.L.

    2008-01-01

    Thick, heterogeneous unsaturated zones away from large streams in desert areas have not previously been considered suitable for artificial recharge from ponds. To test the potential for recharge in these settings, 1.3 ?? 10 6 m3 of water was infiltrated through a 0.36-ha pond along Oro Grande Wash near Victorville, California, between October 2002 and January 2006. The pond overlies a regional pumping depression 117 m below land surface and is located where thickness and permeability of unsaturated deposits allowed infiltration and saturated alluvial deposits were sufficiently permeable to allow recovery of water. Because large changes in water levels caused by nearby pumping would obscure arrival of water at the water table, downward movement of water was measured using sensors in the unsaturated zone. The downward rate of water movement was initially as high as 6 m/d and decreased with depth to 0.07 m/d; the initial time to reach the water table was 3 years. After the unsaturated zone was wetted, water reached the water table in 1 year. Soluble salts and nitrate moved readily with the infiltrated water, whereas arsenic and chromium were less mobile. Numerical simulations done using the computer program TOUGH2 duplicated the downward rate of water movement, accumulation of water on perched zones, and its arrival at the water table. Assuming 10 ?? 10 6 m3 of recharge annually for 20 years, a regional ground water flow model predicted water level rises of 30 m beneath the ponds, and rises exceeding 3 m in most wells serving the nearby urban area.

  7. Unsaturated Zone Flow Changes After Wildfire: A Virtual Experiment Perspective

    NASA Astrophysics Data System (ADS)

    Ebel, B. A.

    2013-12-01

    Wildfire is a frequent disturbance event in the Western U.S. and other regions worldwide. It is well known that wildfire impacts the hydrologic cycle, yet the accompanying changes in unsaturated zone flow are poorly understood. This effort uses unsaturated zone flow simulation for well characterized experimental plots covering north- and south-facing slope aspects for plots both affected and unaffected by wildfire to improve understanding. Comparisons to observed soil-water content and matric potential data establish 'foundation simulations' that lay the groundwork for virtual experiments testing hypotheses developed from interpretation of field and laboratory data. The virtual experiments with the numerical model then extend understanding beyond what could be gleaned from data alone. Unsaturated zone flow is simulated with Hydrus-1D and the field site for this work is within the area affected by the 2010 Fourmile Canyon Fire near Boulder, CO USA. Preliminary work shows that loss of transpiration because of vegetation combustion/mortality caused soils to be wetter at depths greater than 5 cm on both north- and south-facing slopes. Loss of interception by the tree canopy also contributes to wetter subsurface conditions on north-facing slopes. On south-facing slopes, at depths less than 3 cm, the soil was drier after wildfire because of decreases in soil-water retention, confirming hypotheses from field and laboratory measurements.

  8. Evaluation of unsaturated zone air permeability through pneumatic tests

    USGS Publications Warehouse

    Baehr, Arthur L.; Hult, Marc F.

    1991-01-01

    Predicting the steady state distribution of air pressure in the unsaturated zone resulting from a pneumatic test provides a method for determining air-phase permeability. This technique is analogous to the inverse problem of well hydraulics; however, air flow is more complicated than ground water flow because of air compressibility, the Klinkenberg effect, variations in air density and viscosity that result from temperature fluctuations in the unsaturated zone and the possibility of inducing water movement during the pneumatic test. An analysis of these complicating factors reveals that, when induced water movement can be neglected, a linear version of the airflow equation can provide an appropriate approximation for the purpose of determining air-phase permeability. Two analytical solutions for steady state, two-dimensional, axisymmetric airflow to a single well partially screened in the unsaturated zone are developed. One solution applies where there is a stratum of relatively low air permeability, separating the stratum in which the well is completed, from the atmosphere. The other solution applies where there is no separating stratum between the domain and atmosphere. In both situations the water table forms the lower horizontal boundary. Applications of both solutions to determine air permeability from data collected during pneumatic tests are presented.

  9. Hydrogeology of the unsaturated zone, Yucca Mountain, Nevada

    SciTech Connect

    Montazer, P.; Wilson, W.E.

    1985-12-31

    The unsaturated volcanic tuff beneath Yucca Mountain, Nevada, is being evaluated by the US Department of Energy as a host rock for a potential mined geologic repository for high-level radioactive waste. Assessment of site suitability needs an efficient and focused investigative program. A conceptual hydrogeologic model that simulates the flow of fluids through the unsaturated zone at Yucca Mountain was developed to guide the program and to provide a basis for preliminary assessment of site suitability. The study was made as part of the Nevada Nuclear Waste Storage Investigations Project of the US Department of Energy. Thickness of the unsaturated zone is about 1640 to 2460 feet (500 to 750 meters). Based on physical properties, the rocks in the unsaturated zone are grouped for the purpose of this paper into five informal hydrogeologic units. From top to bottom these units are: Tiva Canyon welded unit, Paintbrush nonwelded unit. Topopah Spring welded unit, Calico Hills nonwelded unit, and Crater Flat unit. Welded units have a mean fracture density of 8 to 40 fractures per unit cubic meter, mean matrix porosities of 12 to 23%, matrix hydraulic conductivities with geometric means ranging from 6.5 x 10{sup -6} to 9.8 x 10{sup -6} foot per day (2 x 10{sup -6} to 3 x 10{sup -6} meter per day), and bulk hydraulic conductivities of 0.33 to 33 feet per day (0.1 to 10 meters per day). The nonwelded units have a mean fracture density of 1 to 3 fractures per unit cubic meter, mean matrix porosities of 31 to 46%, and saturated hydraulic conductivities with geometric means ranging from 2.6 x 10{sup -5} to 2.9 x 10{sup -2} foot per day (8 x 10{sup -6} to 9 x 10{sup -3} meter per day). 15 refs., 4 figs., 1 tab.

  10. Injection of Nuclear Rocket Engine Exhaust into Deep Unsaturated Zones

    NASA Astrophysics Data System (ADS)

    Cooper, C. A.; Decker, D.

    2008-05-01

    Nuclear rocket engine technology is being considered as a means of interplanetary vehicle propulsion for a manned mission to Mars. To achieve this, a test and development facility must be constructed to safely run nuclear engines. The testing of nuclear engines in the 1950's and 1960's was accomplished by exhausting the engine gases into the atmosphere, a practice that is no longer acceptable. Injection into deep unsaturated zones of radioactive exhaust gases and water vapor associated with the testing of nuclear rocket engines is being considered as a way of sequestering radionuclides from the environment. Numerical simulations were conducted to determine the ability of an unsaturated zone with the hydraulic properties of Frenchman Flat alluvium at the Nevada Test Site to contain gas-phase radionuclides. Gas and water vapor were injected for two hours at rates of 14.5 kg s-1 and 15 kg s-1, respectively, in an interval between 100 and 430 m below the land surface into alluvium with an intrinsic permeability of 10-11 m2 and porosity of 0.35. The results show that during a test of an engine, radionuclides with at least greater than 10-year half-lives may reach the land surface within several years after injection. Radionuclide transport is primarily controlled by the upward pressure gradient from the point of injection to the lower (atmospheric) pressure boundary condition at the land surface. Radionuclides with half-lives on the order of days should undergo enough decay prior to reaching the land surface. A cooling water vapor injected into the unsaturated zone simultaneously with the exhaust gas will condense within several meters of the injection point and drain downward toward the water table. However, the nearly horizontal hydraulic groundwater gradient present in several of the basins at NTS should limit lateral migration of radionuclides away from the vicinity of injection.

  11. LNAPL Removal from Unsaturated Porous Media using Surfactant Infiltration

    SciTech Connect

    Zhong, Lirong; Oostrom, Martinus

    2012-11-19

    A series of unsaturated column experiments was performed to evaluate light non-aqueous phase liquid (LNAPL) fate and removal during surfactant solution infiltration. Surfactant-LNAPL phase behavior tests were conducted to optimize the remedial solutions. Packed sand and site sediment columns were first processed to establish representative LNAPL smear zone under unsaturated conditions. Infiltration of low-concentration surfactant was then applied in a stepwise flush mode, with 0.3 column pore volume (PV) of solution in each flush. The influence of infiltrated surfactant solution volume and pH on LNAPL removal was assessed. A LNAPL bank was observed at the very front of the first surfactant infiltration in each column, indicating that a very low surfactant concentration is needed to reduce the LNAPL-water interfacial tension sufficiently enough to mobilize trapped LNAPL under unsaturated conditions. More LNAPL was recovered as additional steps of surfactant infiltration were applied. Up to 99% LNAPL was removed after six infiltration steps, with less than 2.0 PV of total surfactant solution application, suggesting surfactant infiltration may be an effective method for vadose zone LNAPL remediation. The influence of pH tested in this study (3.99~10.85) was insignificant because the buffering capacity of the sediment kept the pH in the column higher than the zero point charge, pHzpc, of the sediment and therefore the difference between surfactant sorption was negligible.

  12. New Hydrologic Insights to Advance Geophysical Investigation of the Unsaturated Zone

    NASA Astrophysics Data System (ADS)

    Nimmo, J. R.; Perkins, K. S.

    2015-12-01

    Advances in hydrology require information from the unsaturated zone, especially for problems related to groundwater contamination, water-supply sustainability, and ecohydrology. Unsaturated-zone processes are notoriously difficult to quantify; soils and rocks are visually opaque, spatially variable in the extreme, and easily disturbed by instrument installation. Thus there is great value in noninvasive techniques that produce water-related data of high density in space and time. Methods based on resistivity and electromagnetic waves have already produced significant new understanding of percolation processes, root-zone water retention, influences of evapotranspiration on soil-water, and effects of preferential flow. Further developments are underway for such purposes as noninvasive application to greater depths, increased resolution, adaptation for lab-scale experiments, and calibration in heterogeneous media. Beyond these, however, there is need for a stronger marriage of hydrologic and geophysical knowledge and perspective. Possible means to greater and faster progress include: Apply the latest hydrologic understanding, both pore-scale and macroscopic, to the detection of preferential flow paths and their degree of activation. In the continuing advancement of hardware and techniques, draw creatively from developments in such fields as high-energy physics, medical imaging, astrogeology, high-tech semiconductors, and bioinstrumentation. Sidestep the imaging process where possible to measure essential properties and fluxes more directly. Pose questions that have a strong end-use character, like "how does storm intensity relate to aquifer recharge rate" rather than "what is the shape of the wetting front". The greatest advances in geophysical investigation of the unsaturated zone will come from methods informed by the latest understanding of unsaturated systems and processes, and aimed as directly as possible at the answers to important hydrologic questions.

  13. Modeling water infiltration and pesticides transport in unsaturated zone of a sedimentary aquifer

    NASA Astrophysics Data System (ADS)

    Sidoli, Pauline; Angulo-Jaramillo, Rafael; Baran, Nicole; Lassabatère, Laurent

    2015-04-01

    Groundwater quality monitoring has become an important environmental, economic and community issue since increasing needs drinking water at the same time with high anthropic pressure on aquifers. Leaching of various contaminants as pesticide into the groundwater is closely bound to water infiltration in the unsaturated zone which whom solute transport can occur. Knowledge's about mechanisms involved in the transfer of pesticides in the deep unsaturated zone are lacking today. This study aims to evaluate and to model leaching of pesticides and metabolites in the unsaturated zone, very heterogeneous, of a fluvio-glacial aquifer, in the South-East of France, where contamination of groundwater resources by pesticides is frequently observed as a consequence of intensive agricultural activities. Water flow and pesticide transport were evaluated from column tests under unsaturated conditions and from adsorption batch experiments onto the predominant lithofacies collected, composed of a mixture of sand and gravel. A maize herbicide, S-metolachlor, applied on the study site and worldwide and its two major degradation products (metolachlor ethanesulfonic acid and metolachlor oxanilic acid) were studied here. A conservative tracer, bromide ion, was used to determine water dispersive parameters of porous media. Elution curves were obtained from pesticide concentrations analyzed by an ultra-performance liquid chromatography system interfaced to a triple quadrupole mass spectrometer and from bromide concentrations measured by ionic chromatography system. Experimental data were implemented into Hydrus to model flow and solute transfer through a 1D profile in the vadose zone. Nonequilibrium solute transport model based on dual-porosity model with mobile and immobile water is fitting correctly elution curves. Water dispersive parameters show flow pattern realized in the mobile phase. Exchanges between mobile and immobile water are very limited. Because of low adsorptions onto

  14. Geophysical borehole logging in the unsaturated zone, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Schimschal, Ulrich; Nelson, Philip H.

    1991-01-01

    Borehole geophysical logging for site characterization in the volcanic rocks at the proposed nuclear waste repository at Yucca Mountain, Nevada, requires data collection under rather unusual conditions. Logging tools must operate in rugose, dry holes above the water table in the unsaturated zone. Not all logging tools will operate in this environment, therefore; careful consideration must be given to selection and calibration. A sample suite of logs is presented that demonstrates correlation of geological formations from borehole to borehole, the definition of zones of altered mineralogy, and the quantitative estimates of rock properties. We show the results of an exploratory calculation of porosity and water saturation based upon density and epithermal neutron logs. Comparison of the results with a few core samples is encouraging, particularly because the logs can provide continuous data in boreholes where core samples are not available.

  15. Evolution of the unsaturated zone testing at Yucca Mountain.

    PubMed

    Wang, J S Y; Bodvarsson, G S

    2003-01-01

    The evaluation of the Yucca Mountain site has evolved from intensive surface-based investigations in the early 1980s to current focus on testing in underground drifts. Different periods of site characterization activities and prominent issues concerning the unsaturated zone (UZ) are summarized. Data collection activities have evolved from mapping of faults and fractures to estimation of percolation through tuff layers, and to quantification of seepage into drifts. Evaluation of discrete flow paths in drifts has led to fracture-matrix interaction and matrix diffusion tests over different scales. The effects of tuff interfaces and local faults are evaluated in fractured-welded and porous-nonwelded units. Mobilization of matrix water and redistribution of moisture are measured in thermal tests. Lessons learned from underground tests are used to focus on processes needed for additional quantification. Migration through the drift shadow zone and liquid flow through faults are two important issues that have evolved from current knowledge. PMID:12714299

  16. Evolution of the unsaturated zone testing at Yucca Mountain

    SciTech Connect

    Wang, J.S.Y.; Bodvarsson, G.S.

    2002-09-01

    The evaluation of the Yucca Mountain site has evolved from intensive surface based investigations in the early 1980s to current focus on testing in underground drifts. Different periods of site-characterization activities and prominent issues concerning the unsaturated zone are summarized. Data-collection activities have evolved from mapping of faults and fractures, to estimation of percolation through tuff layers, and to quantification of seepage into drifts. Evaluation of discrete flow paths in drifts has led to fracture-matrix interaction and matrix diffusion tests over different scales. The effects of tuff interfaces and local faults are evaluated in fractured-welded and porous-nonwelded units. Mobilization of matrix water and redistribution of moisture are measured in thermal tests. Lessons learned from underground tests are used to focus on processes needed for additional quantification. Migration through the drift shadow zone and liquid flow through faults are two important issues that have evolved from current knowledge.

  17. 40 CFR 265.278 - Unsaturated zone (zone of aeration) monitoring.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... soils nearby; this background monitoring must be conducted before or in conjunction with the monitoring... a minimum: (1) Soil monitoring using soil cores, and (2) Soil-pore water monitoring using devices... demonstrate in his unsaturated zone monitoring plan that: (1) The depth at which soil and soil-pore...

  18. 40 CFR 265.278 - Unsaturated zone (zone of aeration) monitoring.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... soils nearby; this background monitoring must be conducted before or in conjunction with the monitoring... a minimum: (1) Soil monitoring using soil cores, and (2) Soil-pore water monitoring using devices... demonstrate in his unsaturated zone monitoring plan that: (1) The depth at which soil and soil-pore...

  19. 40 CFR 265.278 - Unsaturated zone (zone of aeration) monitoring.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... soils nearby; this background monitoring must be conducted before or in conjunction with the monitoring... a minimum: (1) Soil monitoring using soil cores, and (2) Soil-pore water monitoring using devices... demonstrate in his unsaturated zone monitoring plan that: (1) The depth at which soil and soil-pore...

  20. 40 CFR 265.278 - Unsaturated zone (zone of aeration) monitoring.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... soils nearby; this background monitoring must be conducted before or in conjunction with the monitoring... a minimum: (1) Soil monitoring using soil cores, and (2) Soil-pore water monitoring using devices... demonstrate in his unsaturated zone monitoring plan that: (1) The depth at which soil and soil-pore...

  1. 40 CFR 265.278 - Unsaturated zone (zone of aeration) monitoring.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... soils nearby; this background monitoring must be conducted before or in conjunction with the monitoring... a minimum: (1) Soil monitoring using soil cores, and (2) Soil-pore water monitoring using devices... demonstrate in his unsaturated zone monitoring plan that: (1) The depth at which soil and soil-pore...

  2. A Research Park for Studying Processes in Unsaturated Fractured Media

    SciTech Connect

    Kristine Baker; Travis McLing; Leah Street; Annette Schafer; Shannon Ansley; Larry Hull; Robert Holt

    2005-01-01

    A field research site has been developed to explore the combined use of physical experiments and mathematical modeling to analyze large-scale infiltration and chemical transport through the unsaturated media overlying the Snake River Plain Aquifer in southeastern Idaho. This site offers opportunities to observe water and contaminant migration influenced by fluid dynamics and microbial activity through heterogeneous-porous and fractured media. At many waste disposal facilities, the presence of toxic or radioactive wastes between the land surface and underlying aquifers poses a serious and ongoing threat to public health and safety. To reduce the risk associated with these industrial and Cold War by-products, a combination of remediation and long-term monitoring will be required.

  3. Colloid suspension stability and transport through unsaturated porous media

    SciTech Connect

    McGraw, M.A.; Kaplan, D.I.

    1997-04-01

    Contaminant transport is traditionally modeled in a two-phase system: a mobile aqueous phase and an immobile solid phase. Over the last 15 years, there has been an increasing awareness of a third, mobile solid phase. This mobile solid phase, or mobile colloids, are organic or inorganic submicron-sized particles that move with groundwater flow. When colloids are present, the net effect on radionuclide transport is that radionuclides can move faster through the system. It is not known whether mobile colloids exist in the subsurface environment of the Hanford Site. Furthermore, it is not known if mobile colloids would likely exist in a plume emanating from a Low Level Waste (LLW) disposal site. No attempt was made in this study to ascertain whether colloids would form. Instead, experiments and calculations were conducted to evaluate the likelihood that colloids, if formed, would remain in suspension and move through saturated and unsaturated sediments. The objectives of this study were to evaluate three aspects of colloid-facilitated transport of radionuclides as they specifically relate to the LLW Performance Assessment. These objectives were: (1) determine if the chemical conditions likely to exist in the near and far field of the proposed disposal site are prone to induce flocculation (settling of colloids from suspension) or dispersion of naturally occurring Hanford colloids, (2) identify the important mechanisms likely involved in the removal of colloids from a Hanford sediment, and (3) determine if colloids can move through unsaturated porous media.

  4. Aspects of hysteresis in unsaturated porous media flow

    NASA Astrophysics Data System (ADS)

    van Duijn, Hans

    2016-04-01

    About 20 years ago, Peter Raats and I wrote a technical note related to the horizontal redistribution in unsaturated porous media with hysteresis in the capillary pressure (P.A.C. Raats & C.J. van Duijn, A note on horizontal redistribution with capillary hysteresis, WWR 31, p. 231-232, 1995). In the first part of my presentation, I will revisit the results of that paper. In particular the cases of unconventional flow, where the water flows from the dry region to the wet region. A comparison will be made with results obtained with the current interface area models as introduced by Gray & Hassanizadeh. I will explain and outline the differences. In the second part, travelling wave solutions of Richards equation with gravity and with hysteresis in both the capillary pressure and relative permeability will be discussed. It will be explained why such solutions oscillate in space-time and how they behave as the hysteresis regularization vanishes.

  5. Noninvasive Quantitative Measurement of Bacterial Growth in Porous Media under Unsaturated-Flow Conditions †

    PubMed Central

    Yarwood, R. R.; Rockhold, M. L.; Niemet, M. R.; Selker, J. S.; Bottomley, P. J.

    2002-01-01

    Glucose-dependent growth of the luxCDABE reporter bacterium Pseudomonas fluorescens HK44 was monitored noninvasively in quartz sand under unsaturated-flow conditions within a 45- by 56- by 1-cm two-dimensional light transmission chamber. The spatial and temporal development of growth were mapped daily over 7 days by quantifying salicylate-induced bioluminescence. A nonlinear model relating the rate of increase in light emission after salicylate exposure to microbial density successfully predicted growth over 4 orders of magnitude (r2 = 0.95). Total model-predicted growth agreed with growth calculated from the mass balance of the system by using previously established growth parameters of HK44 (predicted, 1.2 × 1012 cells; calculated, 1.7 × 1012 cells). Colonization expanded in all directions from the inoculation region, including upward migration against the liquid flow. Both the daily rate of expansion of the colonized zone and the population density of the first day's growth in each newly colonized region remained relatively constant throughout the experiment. Nonetheless, substantial growth continued to occur on subsequent days in the older regions of the colonized zone. The proportion of daily potential growth that remained within the chamber declined progressively between days 2 and 7 (from 97 to 13%). A densely populated, anoxic region developed in the interior of the colonized zone even though the sand was unsaturated and fresh growth medium continued to flow through the colonized zone. These data illustrate the potential of a light transmission chamber, bioluminescent bacteria, and sensitive digital camera technology to noninvasively study real-time hydrology-microbiology interactions associated with unsaturated flow in porous media. PMID:12089048

  6. Noninvasive Quantitative Measurement of Bacterial Growth in Porous Media Under Unsaturated-Flow Conditions

    SciTech Connect

    Yarwood, Rocky; Rockhold, Mark L. ); Niemet, Mike; Selker, John S.; Bottomley, Peter J.

    2002-07-01

    Glucose-dependent growth of the luxCDABE reporter bacterium Pseudomonas fluorescens HK44 was monitored noninvasively in quartz sand under unsaturated-flow conditions within a 45- by 56- by 1-cm two-dimensional light transmission chamber. The spatial and temporal development of growth were mapped daily over 7 days by quantifying salicylate-induced bioluminescence. A nonlinear model relating the rate of increase in light emission after salicylate exposure to microbial density successfully predicted growth over 4 orders of magnitude (r{sup 2}=0.95). Total model-predicted growth agreed with growth calculated from the mass balance of the system by using previously determined growth parameters of HK44 (predicted, 1.2 x 10{sup 12} cells; calculated, 1.7 x 10{sup 12} cells). Colonization expanded in all directions from the inoculation region, including upward migration against the liquid flow. Both the daily rate of expansion of the colonized zone and the population density of the first day's growth in each newly colonized region remained relatively constant throughout the experiment. Nonetheless, substantial growth continued to occur on subsequent days in the older regions of the colonized zone. The proportion of daily potential growth that remained within the chamber declined progressively between days 2 and 7 (from 97 to 13%). A densely populated, anoxic region developed in the interior of the colonized zone even though the sand was unsaturated and fresh growth medium continued to flow through the colonized zone. These data illustrate the potential of a light transmission chamber, bioluminescent bacteria, and sensitive digital camera technology to noninvasively study real-time hydrology-microbiology interactions associated with unsaturated flow in porous media.

  7. 2D experiments for characterizing solute dispersion in unsaturated heterogeneous porous media

    NASA Astrophysics Data System (ADS)

    Jimenez-Martinez, J.; De Anna, P.; Turuban, R.; Tabuteau, H.; Le Borgne, T.; Meheust, Y.

    2012-12-01

    The unsaturated zone plays a key role in the transfer of chemical elements from the surface to the subsurface. Yet, predicting the transport of chemical species through unsaturated porous media is still an open issue. The distribution of water and air clusters creates flow paths that are controlled by the water saturation, with the feature of a large velocity distribution. As saturation decreases, very low velocity zones in regions of trapped fluid coexist with connected fluid clusters with relatively high velocities. As a consequence the dispersion of solute elements strongly depends on the saturation degree. Numerical simulations of unsaturated flows at the pore scale are feasible, but to our knowledge no simulation of solute transport in the water phase during two-phase flow has been achieved yet. Due to technical difficulties, there also exists relatively few laboratory experiments that allow for visualization and quantification of unsaturated flow and transport at the pore scale. We have developed a two-dimensional (2D) horizontal set up, built by lithographic technique and in which a joint injection of the two phases (wetting and non-wetting) provides a controlled homogeneous saturation in the medium. The simultaneous precise measurement of the flow field, the spatial distribution of water and air, and the 2D tracer concentration field, as well as breakthrough curves at different locations, are used to investigate the relationship between the flow field complexity (velocity distribution and its correlation properties) and dispersion properties. Experimental results show non-Fickian transport behaviors, characterized by heavy tailed breakthrough curves, whose characteristics depend on the average saturation.

  8. Effects of thermal vapor diffusion on seasonal dynamics of water in the unsaturated zone

    USGS Publications Warehouse

    Milly, P.C.D.

    1996-01-01

    The response of water in the unsaturated zone to seasonal changes of temperature (T) is determined analytically using the theory of nonisothermal water transport in porous media, and the solutions are tested against field observations of moisture potential and bomb fallout isotopic (36Cl and3H) concentrations. Seasonally varying land surface temperatures and the resulting subsurface temperature gradients induce thermal vapor diffusion. The annual mean vertical temperature gradient is close to zero: however, the annual mean thermal vapor flux is downward, because the temperature-dependent vapor diffusion coefficient is larger, on average, during downward diffusion (occurring at high T) than during upward diffusion (low T). The annual mean thermal vapor flux is shown to decay exponentially with depth; the depth (about 1 m) at which it decays to ??-1 of its surface value is one half of the corresponding decay depth for the amplitude of seasonal temperature changes. This depth-dependent annual mean flux is effectively a source of water, which must be balanced by a flux divergence associated with other transport processes. In a relatively humid environment the liquid fluxes greatly exceed the thermal vapor fluxes, so such a balance is readily achieved without measurable effect on the dynamics of water in the unsaturated zone. However, if the mean vertical water flux through the unsaturated zone is very small (<1 mm y-1), as it may be at many locations in a desert landscape, the thermal vapor flux must be balanced mostly by a matric-potential-induced upward flux of water. This return flux may include both vapor and liquid components. Below any near-surface zone of weather- related fluctuations of matric potential, maintenance of this upward flux requires an increase with depth in the annual mean matric potential; this theoretical prediction is supported by long-term field measurements in the Chihuahuan Desert. The analysis also makes predictions, confirmed by the field

  9. How important is the unsaturated zone in the terrestrial nitrogen budget?

    NASA Astrophysics Data System (ADS)

    Ascott, Matthew; Wang, Lei; Ward, Robert; Stuart, Marianne

    2015-04-01

    Inputs of nitrogen to agricultural land have had significant effects on aquatic and marine ecosystems through eutrophication, algal blooms and habitat loss. In order to manage this problem, terrestrial nitrogen budgets at the national scale have been developed. However, explicit representation of nitrate transport in the subsurface is seldom considered. Using derived estimates of unsaturated zone travel time and nitrate loading at the base of the soil zone, we quantify the total mass of nitrate held in in the unsaturated zone of aquifers in the United Kingdom. In the unsaturated zone of moderate and highly productive aquifers of the UK this is estimated to have peaked in 2008 at 1400 kt N; substantially greater than previous approximations. Currently 70% of the nitrate mass in the unsaturated zone is in the Chalk, with the remainder split between the Permo-Triassic Sandstones, Oolitic Limestones and other less important aquifers. The UK unsaturated zone is now a source of nitrate and in 2014 we estimate the net nitrate flux from the unsaturated zone to groundwater and surface water to be approximately 70 kt N a-1. The mass of nitrate in the unsaturated zone should be considered in future terrestrial nitrogen budgets to improve national scale ecosystem management.

  10. Oxygen profiling of the unsaturated zone using direct push drilling.

    PubMed

    Sopilniak, A; Elkayam, R; Lev, O; Elad, T

    2015-09-01

    A methodology for oxygen profile measurements in the unsaturated zone is developed based on direct push drilling using sampling liners equipped with homemade silicone septa. The oxygen measurement is carried out by puncturing the septum with a commercial retractable optode needle fitted with a fluorescent tip. Metrological characteristics and method validation were carried out under laboratory conditions using different levels of oxygen and various water contents. The relative standard deviations under dry and water saturated soil conditions were less than 0.3% and 5% for 0.5 mg L(-1) of oxygen and less than 2% and 3% for 9 mg L(-1). Field demonstrations in a calcareous-sandstone soil aquifer treatment system with a layered clayey, marl and sandstone lithology of widely different water contents provided down to 30 m deep profiles of the dissolved oxygen level with less than 1.5 m spatial resolution. A single sensor was used for over 50 field measurements, though recalibration was required after approximately 30 measurements due to the deterioration of the fluorescent tip. PMID:26245519

  11. Numerical Simulation of Moisture Flux in Deep Unsaturated Zones

    NASA Astrophysics Data System (ADS)

    Cooper, C.; Young, M.; Sharpe, S.; Miller, J.

    2003-04-01

    Understanding the rate and direction of liquid water movement in the valley fill sediments in the northern Mojave Desert (USA) is important for understanding groundwater recharge and near-surface soil water budgets. In some areas, the upward hydraulic gradient in the unsaturated zone drives liquid water upward. We used the multiphase, multicomponent simulator TOUGH2 to identify hydraulic processes and their magnitudes controlling liquid and vapor flux through a 250 m, one-dimensional column of unconsolidated sediment. Ten samples of unconsolidated sediment were collected from depths ranging from land surface to 31 m below land surface. The samples were repacked to original bulk density and analyzed for unsaturated hydraulic properties using an open-flow centrifuge. In the model, evaporation was simulated by prescribing the gas phase pressure at a thin, highly permeable "atmospheric" grid block at the land surface with zero relative humidity. The rest of the column was initially prescribed a gas pressure that was the sum of the ambient dry air pressure and the saturated vapor pressure at the assumed temperature. Root water uptake was modeled using the reservoir-engineering concept of a productivity index for a well, where the root operated against a slight, constant, prescribed pressure less than the reference atmospheric pressure. A 24,000-year precipitation sequence, generated from biotic distributions (e.g. ostracodes and pack-rat middens), was prescribed at the upper boundary. For our initial and boundary conditions, the simulations show that liquid flow is upward with velocities ranging between zero and 5 x 10-5 mm yr-1, depending on depth below ground surface. The zero flux plane fluctuates in depth between 14 and 17 meters, below which liquid flow is downward. In the absence of plants, liquid flow is downward throughout the entire profile and simulation period. Our simulations show that the "memory" of the system is on the order of 10,000 years; that is, the

  12. Numerical study of variable-density flow and transport in unsaturated-saturated porous media.

    PubMed

    Liu, Yi; Kuang, Xingxing; Jiao, Jiu Jimmy; Li, Jiang

    2015-11-01

    Dense contaminant or solute transport in the unsaturated-saturated aquifer commonly exists in the natural environment. However, the influence of hydraulic properties of the unsaturated soil on penetration process of variable density flow in an unsaturated-saturated aquifer system is rarely investigated. In this study, a variable density, variably saturated flow and transport model based on FEFLOW is used to systematically investigate the penetration process of the solute through the unsaturated-saturated aquifer system, with a focus on the influence of the hydraulic parameters of the unsaturated soil on the penetration process. Vertical center of mass, and its speed and acceleration, are used to identify different stages of the penetration process through the unsaturated-saturated aquifer. The hydraulic parameters in the van Genuchten-Mualem model (VGM) affect the water content distribution in the unsaturated zone, subsequently the penetration time through the unsaturated zone. Through influencing the thickness of the transition zone (0.1-0.9 maximum concentration of the plume) when the plume reaches the water table, the hydraulic parameters affect the accumulation time of the solute at the boundary layer in the saturated zone. Thus, the process in not only the unsaturated but also the saturated zones is influenced by the change of the hydraulic properties of the unsaturated zone. Furthermore, the results show that the instabilities start to occur at the zone with high water content (90% of maximum saturation) in the capillary fringe. Freshwater intrudes into the zone with high water content when fingers are completely developed at the entire system. The length of freshwater intrusion above the water table has a negative correlation with the fitting parameter alpha in the VGM model. The influence of the density difference of the solute on the penetration processes is insignificant in the unsaturated zone but significant in the saturated zone. Sensitive analysis for

  13. Numerical study of variable-density flow and transport in unsaturated-saturated porous media

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Kuang, Xingxing; Jiao, Jiu Jimmy; Li, Jiang

    2015-11-01

    Dense contaminant or solute transport in the unsaturated-saturated aquifer commonly exists in the natural environment. However, the influence of hydraulic properties of the unsaturated soil on penetration process of variable density flow in an unsaturated-saturated aquifer system is rarely investigated. In this study, a variable density, variably saturated flow and transport model based on FEFLOW is used to systematically investigate the penetration process of the solute through the unsaturated-saturated aquifer system, with a focus on the influence of the hydraulic parameters of the unsaturated soil on the penetration process. Vertical center of mass, and its speed and acceleration, are used to identify different stages of the penetration process through the unsaturated-saturated aquifer. The hydraulic parameters in the van Genuchten-Mualem model (VGM) affect the water content distribution in the unsaturated zone, subsequently the penetration time through the unsaturated zone. Through influencing the thickness of the transition zone (0.1-0.9 maximum concentration of the plume) when the plume reaches the water table, the hydraulic parameters affect the accumulation time of the solute at the boundary layer in the saturated zone. Thus, the process in not only the unsaturated but also the saturated zones is influenced by the change of the hydraulic properties of the unsaturated zone. Furthermore, the results show that the instabilities start to occur at the zone with high water content (90% of maximum saturation) in the capillary fringe. Freshwater intrudes into the zone with high water content when fingers are completely developed at the entire system. The length of freshwater intrusion above the water table has a negative correlation with the fitting parameter alpha in the VGM model. The influence of the density difference of the solute on the penetration processes is insignificant in the unsaturated zone but significant in the saturated zone. Sensitive analysis for

  14. Investigations of the unsaturated zone at two radioactive waste disposal sites in Lithuania.

    PubMed

    Skuratovič, Žana; Mažeika, Jonas; Petrošius, Rimantas; Martma, Tõnu

    2016-01-01

    The unsaturated zone is an important part of the water cycle, governed by many hydrological and hydrogeological factors and processes and provide water and nutrients to the terrestrial ecosystem. Besides, the soils of the unsaturated zone are regarded as the first natural barrier to a large extent and are able to limit the spread of contaminants depending on their properties. The unsaturated zone provides a linkage between atmospheric moisture, groundwater, and seepage of groundwater to streams, lakes, or other surface water bodies. The major difference between water flow in saturated and unsaturated soils is that the hydraulic conductivity, which is conventionally assumed to be a constant in saturated soils, is a function of the degree of saturation or matrix suction in the unsaturated soils. In Lithuania, low and intermediate level radioactive wastes generated from medicine, industry and research were accumulated at the Maisiagala radioactive waste repository. Short-lived low and intermediate levels radioactive waste, generated during the operation of the Ignalina Nuclear Power Plant (INPP) and arising after the INPP decommissioning will be disposed of in the near surface repository close to the INPP (Stabatiske site). Extensive data sets of the hydraulic properties and water content attributed to unsaturated zone soil profiles of the two radioactive waste disposal sites have been collected and summarized. Globally widespread radionuclide tritium ((3)H) and stable isotope ratio ((18)O/(16)O and (2)H/(1)H) distribution features were determined in precipitation, unsaturated zone soil moisture profiles and groundwater. PMID:26586231

  15. Improvement of the hillslope-storage Boussinesq model by considering lateral flow in the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Kong, Jun; Shen, Chengji; Luo, Zhaoyang; Hua, Guofen; Zhao, Hongjun

    2016-04-01

    Unsaturated flow is an important factor that affects groundwater motion. Among various drainage models, the nonlinear Hillslope-storage Boussinesq (HSB) model has been commonly used to predict water flux along a slope. In this study, we improved this model by considering lateral flow in the unsaturated zone. Using modified van Genuchten functions, we analytically expressed the concept of equivalent propagation thickness in the vadose zone. This analytical expression was then incorporated into the HSB model to reflect two different stages of the drainage process and to simulate the hillslope drainage process more accurately. The model results indicated that lateral flow has significant effects in the unsaturated zone during the hillslope drainage process. Even in sandy aquifers, the amount of water contributed by the unsaturated zone is a key factor that enables a decrease in the water table during the middle and late stages of the process. A comparison between the measured and simulated results based on both convergent-type and divergent-type hillslope drainage processes revealed that the thickness of the saturated zone decreases as the unsaturated flow increases. This study emphasizes the necessity of considering unsaturated flow in the HSB model to improve the accuracy of predicting groundwater outflow rates and develop more accurate hydrographs. The concept of equivalent propagation thickness also provides a criterion for assessing the importance of unsaturated lateral flow for future drainage research.

  16. Understanding Fluid and Contaminant Movement in the Unsaturated Zone Using the INEEL Vadose Zone Monitoring System

    SciTech Connect

    Hubbell, J. M.; Mattson, E. D.; Sisson, J. B.; Magnuson, S. O.

    2002-02-26

    DOE has hundreds of contaminated facilities and waste sites requiring cleanup and/or long-term monitoring. These contaminated sites reside in unsaturated soils (i.e. the vadose zone) above the water table. Some of these sites will require active remediation activities or removal while other sites will be placed under institutional controls. In either case, evaluating the effectiveness of the remediation strategy or institutional controls will require monitoring. Classical monitoring strategies implemented at RCRA/CERCLA sites require ground water sampling for 30 years following closure. The overall effectiveness of ground water sampling is diminished due to the fact that by the time you detect chemical transport from a waste site, a major contamination plume likely exists in the vadose zone and the aquifer. This paper suggests a more effective monitoring strategy through monitoring near the contaminant sites within the vadose zone. Vadose zone monitoring allows for quicker detection of potential contaminant transport. The INEEL Vadose Zone Monitoring System (VZMS) is becoming an accepted, cost effective monitoring technology for assessing contaminant transport at DOE facilities. This paper describes the technologies employed in the VZMS and describes how it was used at several DOE facilities. The INEEL VZMS has provided the information in developing and validating both conceptual and risk assessment models of contaminant transport at the Idaho National Engineering and Environmental Laboratory (INEEL), Oak Ridge National Laboratory (ORNL), Savannah River Site (SRS) and the Hanford site. These DOE sites exhibit a broad range of meteorologic, hydrologic and geologic conditions representative of various common geologic environments. The VZMS is comprised of advanced tensiometers, water content sensors, temperature sensors and soil and gas samplers. These instruments are placed at multiple depths in boreholes and allows for the detection of water movement in the

  17. Storage and mobilization of natural and septic nitrate in thick unsaturated zones, California

    NASA Astrophysics Data System (ADS)

    Izbicki, John A.; Flint, Alan L.; O'Leary, David R.; Nishikawa, Tracy; Martin, Peter; Johnson, Russell D.; Clark, Dennis A.

    2015-05-01

    Mobilization of natural and septic nitrate from the unsaturated zone as a result of managed aquifer recharge has degraded water quality from public-supply wells near Yucca Valley in the western Mojave Desert, California. The effect of nitrate storage and potential for denitrification in the unsaturated zone to mitigate increasing nitrate concentrations were investigated. Storage of water extractable nitrate in unsaturated alluvium up to 160 meters (m) thick, ranged from 420 to 6600 kilograms per hectare (kg/ha) as nitrogen (N) beneath undeveloped sites, from 6100 to 9200 kg/ha as N beneath unsewered sites. Nitrate reducing and denitrifying bacteria were less abundant under undeveloped sites and more abundant under unsewered sites; however, δ15N-NO3, and δ18O-NO3 data show only about 5-10% denitrification of septic nitrate in most samples-although as much as 40% denitrification occurred in some parts the unsaturated zone and near the top of the water table. Storage of nitrate in thick unsaturated zones and dilution with low-nitrate groundwater are the primary attenuation mechanisms for nitrate from septic discharges in the study area. Numerical simulations of unsaturated flow, using the computer program TOUGH2, showed septic effluent movement through the unsaturated zone increased as the number and density of the septic tanks increased, and decreased with increased layering, and increased slope of layers, within the unsaturated zone. Managing housing density can delay arrival of septic discharges at the water table, especially in layered unsaturated alluvium, allowing time for development of strategies to address future water-quality issues.

  18. Storage and mobilization of natural and septic nitrate in thick unsaturated zones, California

    USGS Publications Warehouse

    Izbicki, John A.; Flint, Alan L.; O'Leary, David R.; Nishikawa, Tracy; Martin, Peter; Johnson, Russell D.; Clark, Dennis A.

    2015-01-01

    Mobilization of natural and septic nitrate from the unsaturated zone as a result of managed aquifer recharge has degraded water quality from public-supply wells near Yucca Valley in the western Mojave Desert, California. The effect of nitrate storage and potential for denitrification in the unsaturated zone to mitigate increasing nitrate concentrations were investigated. Storage of water extractable nitrate in unsaturated alluvium up to 160 meters (m) thick, ranged from 420 to 6600 kilograms per hectare (kg/ha) as nitrogen (N) beneath undeveloped sites, from 6100 to 9200 kg/ha as N beneath unsewered sites. Nitrate reducing and denitrifying bacteria were less abundant under undeveloped sites and more abundant under unsewered sites; however, δ15N–NO3, and δ18O–NO3 data show only about 5–10% denitrification of septic nitrate in most samples—although as much as 40% denitrification occurred in some parts the unsaturated zone and near the top of the water table. Storage of nitrate in thick unsaturated zones and dilution with low-nitrate groundwater are the primary attenuation mechanisms for nitrate from septic discharges in the study area. Numerical simulations of unsaturated flow, using the computer program TOUGH2, showed septic effluent movement through the unsaturated zone increased as the number and density of the septic tanks increased, and decreased with increased layering, and increased slope of layers, within the unsaturated zone. Managing housing density can delay arrival of septic discharges at the water table, especially in layered unsaturated alluvium, allowing time for development of strategies to address future water-quality issues.

  19. Unsaturated zone arsenic distribution and implications for groundwater contamination.

    PubMed

    Reedy, Robert C; Scanlon, Bridget R; Nicot, Jean-Philippe; Tachovsky, J Andrew

    2007-10-15

    Arsenic compounds have been applied at the land surface as pesticides in agricultural areas globally. The purpose of this study was to evaluate the fate of anthropogenic arsenic applications related to agriculture, using arsenic applications on cotton in the southern High Plains (SHP), Texas, as a case study and examining possible linkages with contamination of the underlying Ogallala aquifer in this region, where 36% of wells exceed the new EPA 10 microg/L standard. Unsaturated zone soil samples were collected from boreholes beneath natural ecosystems (grassland/ shrubland) to provide a control (no arsenic application) (5 profiles) and cotton cropland (20 profiles) for analyses of water-extractable arsenic, vanadium, phosphate, chloride, and nitrate. Natural ecosystem profiles have high arsenic concentrations at depth (maximum of 7.2-69.6 microg As/ kg dry soil at 5.9-21.4 m depth) that are attributed to a geologic source. Most profiles beneath cotton cropland have high arsenic concentrations within the upper meter (profile means 1.7 to 31.6 microg/kg) that correlate with phosphate (r = 0.70, p < 0.01) and are attributed to anthropogenic arsenic application associated with phosphate fertilizer application. High arsenic concentrations at >1 m depth (profile means < or =36.3 microg/kg) found in cropland profiles are attributed to a geologic source because of similarity with profiles beneath natural ecosystems, lack of correlation with phosphate, and pore-water ages that predate anthropogenic arsenic application in many profiles. GIS analyses showed poor correlations between groundwater arsenic and percent cultivated land (r = -0.15, p < 0.01), groundwater nitrate (r = 0.30, p < 0.01), and water table depth (r= -0.31, p < 0.01), further supporting the idea that anthropogenic-derived arsenic in the shallow subsurface is not linked to groundwater arsenic contamination in this region. PMID:17993128

  20. Characterization of chloride transport in the unsaturated zone near salted road

    NASA Astrophysics Data System (ADS)

    Lax, Samanta; Peterson, Eric W.

    2009-09-01

    The application of road salts as deicing agents contributes to the anthropogenic loading of chloride (Cl-) on the environment. Using a 2D solute model, the potential of the unsaturated zone to serve as a reservoir and the mechanisms controlling the movement of Cl- were examined. Physical properties and initial pore-water Cl- concentrations were derived from an array of soil borings. Initial pore-water concentrations show the presence of a Cl- “slug” approximately 0.75 m below the surface. Simulations show that within the unsaturated zone, Cl- transport is predominantly vertical, driven by molecular diffusion. After a 1-year simulation, a Cl- slug similar to the background observation was noted. While Cl- is retained in the unsaturated zone, a net loss of Cl- from the unsaturated zone was simulated for the first 10 years. In year 11, an equilibrium between the Cl- input and output is achieved. The presence of Cl- in the unsaturated zone becomes a long-term source of chloride to the groundwater, which eventually discharges into the surface water. Historically, surface water chemistry data support the continual discharge of chloride to the surface water in the area, further supporting the hypothesis that the unsaturated zone serves as a Cl- reservoir.

  1. Apparent Anisotropic Diffusion of SF6 in a Deep Arid Unsaturated Zone

    NASA Astrophysics Data System (ADS)

    Green, C. T.; Walvoord, M. A.; Andraski, B. J.; Striegl, R. G.; Stonestrom, D. A.

    2014-12-01

    Gas transport in the unsaturated zone affects contaminant dispersal, remediation, interpretation of groundwater travel times from atmospheric tracers, and mass-budgets of environmentally important gases. Although deep unsaturated zone transport of gases is commonly treated as dominated by Fickian diffusion, previous observations at the Amargosa Desert Research Site have shown that the transport rates of various gas phase contaminants are faster than expected from standard models of diffusive transport. In this study, we use a multi-model approach to analyze results of a gas-tracer (SF6) test to clarify factors affecting gas transport in a deep unsaturated zone. Thirteen separate models with distinct diffusivity structures were calibrated to the tracer-test data. Models were compared on the basis of Akaike Information Criteria estimates of posterior model probability. The greatest posterior probability occurred for a model with significant anisotropy of diffusivity in addition to varying apparent diffusivity among vertically distributed sampling locations. Some horizontal diffusivities were greater than expected for purely diffusive transport, with values approaching free-air diffusivity (tortuosity ≈ 0.6 to 1). The magnitudes of the high apparent diffusivities were consistent with advective oscillations propagating through unsaturated-zone strata based on an analysis of barometric and unsaturated-zone air pressure time series. These results indicate that point source gases in layered unsaturated zones can spread laterally more quickly, and produce higher peak concentrations, than predicted by isotropic Fickian diffusion models.

  2. FITTING OF THE DATA FOR DIFFUSION COEFFICIENTS IN UNSATURATED POROUS MEDIA

    SciTech Connect

    B. Bullard

    1999-05-01

    The purpose of this calculation is to evaluate diffusion coefficients in unsaturated porous media for use in the TSPA-VA analyses. Using experimental data, regression techniques were used to curve fit the diffusion coefficient in unsaturated porous media as a function of volumetric water content. This calculation substantiates the model fit used in Total System Performance Assessment-1995 An Evaluation of the Potential Yucca Mountain Repository (TSPA-1995), Section 6.5.4.

  3. Vapor-phase interactions and diffusion of organic solvents in the unsaturated zone

    USGS Publications Warehouse

    Roy, W.R.; Griffin, R.A.

    1990-01-01

    This article presents an analysis of the interactions and static movement of 37 organic solvents as vapors through the unsaturated soil zone. The physicochemical interactions of the organic vapors with unsaturated soil materials were emphasized with focus on diffusive, and adsorptive interactions. Fick's Law and porous media diffusion coefficients for most of the solvent vapors were either compiled or estimated; coefficients were not available for some of the fluorinated solvents. The adsorption of some of the solvent vapors by silica was concluded to be due to hydrogen bond formation with surface silanol groups. Heats of adsorption data for different adsorbents were also compiled. There were very few data on the adsorption of these solvent vapors by soils, but it appears that the magnitude of adsorption of nonpolar solvents is reduced as the relative humidity of the vapor-solid system is increased. Consequently, the interaction of the vapors may then separated into two processes; (1) gas-water partitioning described by Henry's Law constants, and (2) solid-water adsorption coefficients which may be estimated from liquid-solid partition coefficients (Kd values). ?? 1990 Springer-Verlag New York Inc.

  4. Time-series analysis for determining vertical air permeability in unsaturated zones

    SciTech Connect

    Lu, N.

    1999-01-01

    The air pressure in the unsaturated subsurface changes dynamically as the barometric pressure varies with time. Depending on the material properties and boundary conditions, the intensity of the correlation between the atmospheric and subsurface pressures may be evidenced in two persistent patterns: (1) the amplitude attenuation; and (2) the phase lag for the principal modes, such as the diurnal, semidiurnal, and 8-h tides. The amplitude attenuation and the phase lag generally depend on properties that can be classified into two categories: (1) The barometric pressure parameters, such as the apparent pressure amplitudes and frequencies controlled by the atmospheric tides and others; and (2) the material properties of porous media, such as the air viscosity, air-filled porosity, and permeability. Based on the principle of superposition and a Fourier time-series analysis, an analytical solution for predicting the subsurface air pressure variation caused by the atmospheric pressure fluctuation is presented. The air permeability (or pneumatic diffusivity) can be quantitatively determined by using the calculated amplitude attenuations (or phase lags) and the appropriate analytical relations among the parameters of the atmosphere and the porous medium. An analysis using the field data shows that the Fourier time-series analysis may provide a potentially reliable and simple method for predicting the subsurface barometric pressure variation and for determining the air permeability of unsaturated zones.

  5. Impacts of thickening unsaturated zone on groundwater recharge in the North China Plain

    NASA Astrophysics Data System (ADS)

    Cao, Guoliang; Scanlon, Bridget R.; Han, Dongmei; Zheng, Chunmiao

    2016-06-01

    Unsustainable groundwater development shown by rapid groundwater depletion in the North China Plain (NCP) underscores the need to quantify spatiotemporal variability in groundwater recharge for improved management of the resource. The objective of this study was to assess spatiotemporal variability in recharge in response to thickening of the unsaturated zone in the NCP. Recharge was estimated by linking a soil water balance (SWB) model, on the basis of monthly meteorological data, irrigation applications, and soil moisture monitoring data (1993-2008), to the water table using a deep unsaturated zone flow model. The dynamic bottom boundary (water table) position was provided by the saturated zone flow component, which simulates regional pumping. The model results clearly indicate the effects of unsaturated zone thickening on both temporal distribution and magnitude of recharge: smoothing temporal variability in recharge, and increasing unsaturated storage and lag time between percolation and recharge. The thickening unsaturated zone can result in average recharge reduction of up to ∼70% in loam soils with water table declines ⩾30 m. Declining groundwater levels with irrigation sourced by groundwater converts percolation to unsaturated zone storage, averaging 14 mm equivalent water depth per year in mostly loam soil over the study period, accounting for ∼30% of the saturated groundwater storage depletion. This study demonstrates that, in thickening unsaturated zones, modeling approaches that directly equate deep drainage with recharge will overestimate the amount and underestimate the time lag between percolation and recharge, emphasizing the importance of more realistic simulation of the continuity of unsaturated and saturated storage to provide more reliable estimates of spatiotemporal variability in recharge.

  6. Time-domain reflectometry probing systems for the monitoring of hydrological processes in the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Kallioras, A.; Khan, A.; Piepenbrink, M.; Pfletschinger, H.; Koniger, F.; Dietrich, P.; Schuth, C.

    2016-08-01

    Precise measurements of the downward movement of precipitation through the unsaturated zone, as well as return flow of moisture to the atmosphere via evaporation, have always been challenging in regard to in-situ monitoring techniques. This study investigates the profile of volumetric water-content fluctuations within the unsaturated zone through a combination of field techniques, including in-situ measurements of the volumetric porewater content at different depths using specially designed time-domain reflectometry (TDR) probes. The probes are installed through direct-push vibro-coring methods, at significant depths within the unsaturated zone, providing continuous readings of the soil-moisture content throughout the unsaturated column. The measured waveform is analyzed by using the inverse modeling approach resulting in an apparent relative dielectric permittivity profile of the surrounding medium along the TDR probe length. The approach sufficiently analyzes the mechanisms of water fluxes through significant depths within the unsaturated zone, which in turn can be used to quantify groundwater recharge at areas where the unsaturated zone hydrology plays a key role in the recharge of the underlying aquifers (such as arid and hydrologically sensitive areas). The approach was applied at an experimental field site in the Upper Rhine Valley, Germany.

  7. Time-domain reflectometry probing systems for the monitoring of hydrological processes in the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Kallioras, A.; Khan, A.; Piepenbrink, M.; Pfletschinger, H.; Koniger, F.; Dietrich, P.; Schuth, C.

    2016-05-01

    Precise measurements of the downward movement of precipitation through the unsaturated zone, as well as return flow of moisture to the atmosphere via evaporation, have always been challenging in regard to in-situ monitoring techniques. This study investigates the profile of volumetric water-content fluctuations within the unsaturated zone through a combination of field techniques, including in-situ measurements of the volumetric porewater content at different depths using specially designed time-domain reflectometry (TDR) probes. The probes are installed through direct-push vibro-coring methods, at significant depths within the unsaturated zone, providing continuous readings of the soil-moisture content throughout the unsaturated column. The measured waveform is analyzed by using the inverse modeling approach resulting in an apparent relative dielectric permittivity profile of the surrounding medium along the TDR probe length. The approach sufficiently analyzes the mechanisms of water fluxes through significant depths within the unsaturated zone, which in turn can be used to quantify groundwater recharge at areas where the unsaturated zone hydrology plays a key role in the recharge of the underlying aquifers (such as arid and hydrologically sensitive areas). The approach was applied at an experimental field site in the Upper Rhine Valley, Germany.

  8. Modeling transient streaming potentials in coupled saturated-unsaturated zone flow to a pumping well

    NASA Astrophysics Data System (ADS)

    Malama, B.

    2012-12-01

    A semi-analytical model for transient response of streaming potentials (SP) to pumping in an unconfined aquifer, taking into account unsaturated zone flow, is presented. Flow in the unsaturated zone is modeled with a linearized Richards' equation with the moisture retention curve and unsaturated hydraulic conduc- tivity assumed to be exponential functions of matric potential. For the case presented here, the same sorption number is assumed for moisture retention and unsaturated hydraulic conductivity. The ratio of the unsaturated to satu- rated electrokinetic coupling coefficient is described by Cℓ,r = kr Sw-(d+1), where kr is relative hydraulic conductivity, Sw is saturation, and d is Archie's second exponent. Hence, based on the assumption of an exponential moisture retention curve, Cℓ,r is also an exponential function of matric potential. Model predicted responses in the saturated and unsaturated zones are compared with measured SP responses to pumping in a bench-scale experimental setup that simulates a radially bounded unconfined aquifer. Potential for using SP responses to esti- mate saturated and unsaturated hydraulic parameters is evaluated. 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. This research is funded by WIPP programs administered by the Office of Environmental Management (EM) of the U.S Department of Energy.

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

    SciTech Connect

    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 fractured 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.

  10. Quantification of groundwater recharge through application of pilot techniques in the unsaturated zone.

    NASA Astrophysics Data System (ADS)

    Kallioras, Andreas; Piepenbrink, Matthias; Schuth, Christoph; Pfletschinger, Heike; Dietrich, Peter; Koeniger, Franz; Rausch, Randolf

    2010-05-01

    Accurate determination of groundwater recharge is a key issue for the "smart mining" of groundwater resources. Groundwater recharge estimation techniques depend on the investigated hydrologic zone, and therefore main approaches are based on (a) unsaturated zone, (b) saturated zone and (c) surface water studies. This research contributes to the determination of groundwater recharge by investigating the infiltration of groundwater through the unsaturated zone. The investigations are conducted through the application of a combination of different pilot field as well as lab techniques. The field techniques include the installation of specially designed Time Domain Reflectometry (TDR) sensors, at different depths within the unsaturated zone for in-situ and continuous measurements of the volumetric pore water content. Additionally, the extraction of pore water -for analysis of its isotopic composition- from multilevel undisturbed soil samples through significant depths within the unsaturated zone column, enables the dating of the groundwater age through the determination of its isotopic composition. The in-situ investigation of the unsaturated zone is complemented by the determination of high resolution temperature profiles. The installation of the pilot TDR sensors is achieved by using direct push methods at significant depths within the unsaturated zone, providing continuous readings of the soil moisture content. The direct push methods are also ideal for multilevel sampling of undisturbed -without using any drilling fluids which affect the isotopic composition of the containing pore water- soil and consequent extraction of the included pore water for further isotopic determination. The pore water is extracted by applying the method of azeotropic distillation; a method which has the least isotopic fractionation effects on groundwater samples. The determination of different isotopic signals such as 18O, 2H, 3H, and 36Cl, aims to the investigation of groundwater transit

  11. Percolation induced heat transfer in deep unsaturated zones

    USGS Publications Warehouse

    Lu, N.; LeCain, G.D.

    2003-01-01

    Subsurface temperature data from a borehole located in a desert wash were measured and used to delineate the conductive and advective heat transfer regimes, and to estimate the percolation quantity associated with the 1997-1998 El Ni??no precipitation. In an arid environment, conductive heat transfer dominates the variation of shallow subsurface temperature most of the time, except during sporadic precipitation periods. The subsurface time-varying temperature due to conductive heat transfer is highly correlated with the surface atmospheric temperature variation, whereas temperature variation due to advective heat transfer is strongly correlated with precipitation events. The advective heat transfer associated with precipitation and infiltration is the focus of this paper. Disruptions of the subsurface conductive temperature regime, associated with the 1997-1998 El Ni??no precipitation, were detected and used to quantify the percolation quantity. Modeling synthesis using a one-dimensional coupled heat and unsaturated flow model indicated that a percolation per unit area of 0.7 to 1.3 m height of water in two weeks during February 1998 was responsible for the observed temperature deviations down to a depth of 35.2 m. The reported study demonstrated quantitatively, for the first time, that the near surface temperature variation due to advective heat transfer can be significant at a depth greater than 10 m in unsaturated soils and can be used to infer the percolation amount in thick unsaturated soils.

  12. Disposal of high-level radioactive wastes in the unsaturated zone: Technical considerations and response to comments

    NASA Astrophysics Data System (ADS)

    Hackbarth, C. J.; Nicholson, T. J.; Evans, D. D.

    1985-10-01

    On July 22, 1985, the U. S. Nuclear Regulatory Commission (NRC) promulgated amendments to 10 CFR Part 60 concerning disposal of high level radioactive waste (HLW) in geologic repositories in the unsaturated zone (50 FR 29641). The principal technical issues considered by the NRC staff during the development of these amendments was discussed. Certain technical discussions originally presented in draft NUREG-1046 were revised based on public comment letters and an increasing understanding of the physical, geochemical, and hydrological processes operative in unsaturated geologic media. The following issues related to disposal of HLW within the unsaturated zone were discussed: hydrogeologic properties and conditions, heat dissipation and temperature, geochemistry, retrievability, potential for exhumation of the radioactive waste by natural causes and by human intrusion, the effects of future climatic changes on the level of the regional water table, and transport of radionuclides in the gaseous state. On July 22, 1985, the U. S. Nuclear Regulatory Commission (NRC) promulgated amendments to 10 CFR meter depth for waste emplacement, limitations on exploratory boreholes, backfill requirements, waste package design criteria, and provisions for ventilation.

  13. Pore-scale mechanisms for the enhancement of mixing in unsaturated porous media and implications for chemical reactions

    NASA Astrophysics Data System (ADS)

    Jiménez-Martínez, Joaquín.; Anna, Pietro de; Tabuteau, Hervé; Turuban, Régis; Borgne, Tanguy Le; Méheust, Yves

    2015-07-01

    Porous media in which different fluid phases coexist are common in nature (e.g., vadose zone and gas-oil reservoirs). In partially saturated porous media, the intricate spatial distributions of the wetting and nonwetting phases causes their flow to be focused onto preferential paths. Using a novel 2-D experimental setup allowing pore-scale measurement of concentration fields in a controlled unsaturated flow, we highlight mechanisms by which mixing of an invading fluid with the resident fluid is significantly enhanced when decreasing saturation. The mean scalar dissipation rate is observed to decrease slowly in time, while under saturated conditions it decays rapidly. This slow decrease is due to sustained longitudinal solute fingering, which causes concentration gradients to remain predominantly transverse to the average flow. Consequently, the effective reactivity is found to be much larger than under saturated conditions. These results provide new insights into the role that multiphase flows play on mixing/reaction in porous media.

  14. Data from a thick unsaturated zone in Joshua Tree, San Bernardino County, California, 2007--09

    USGS Publications Warehouse

    Burgess, Matthew; Izbicki, John; Teague, Nicholas; O'Leary, David R.; Clark, Dennis; Land, Michael

    2012-01-01

    Data were collected on the physical properties of unsaturated alluvial deposits, the chemical composition of leachate extracted from unsaturated alluvial deposits, the chemical and isotopic composition of groundwater and unsaturated-zone water, and the chemical composition of unsaturated-zone gas at four monitoring sites in the southwestern part of the Mojave Desert in the town of Joshua Tree, San Bernardino County, California. The presence of denitrifying and nitrate-reducing bacteria from unsaturated alluvial deposits was evaluated for two of these monitoring sites that underlie unsewered residential development. Four unsaturated-zone monitoring sites were installed in the Joshua Tree area—two in an unsewered residential development and two adjacent to a proposed artificial-recharge site in an undeveloped area. The two boreholes in residential development areas were installed by using the ODEX air-hammer method. One borehole was drilled through the unsaturated zone to a depth of 541 ft (feet) below land surface; a well screened across the water table was installed. Groundwater was sampled from this well. The second borehole was drilled to a depth of 81 ft below land surface. Drilling procedures, lithologic and geophysical data, construction details, and instrumentation placed in these boreholes are described. Core material was analyzed for water content, bulk density, matric potential, particle size, and water retention. The leachate from over 500 subsamples of cores and cuttings was analyzed for soluble anions, including fluoride, sulfate, bromide, chloride, nitrate, nitrite, and orthophosphate. Groundwater was analyzed for major ions, inorganic compounds, select trace elements, and isotopic composition. Unsaturated-zone water from suction-cup lysimeters was analyzed for major ions, inorganic compounds, select trace elements, and isotopic composition. Unsaturated-zone gas samples were analyzed for argon, oxygen, nitrogen, methane, carbon dioxide, ethane

  15. Impact of microbial growth on water flow and solute transport in unsaturated porous media

    SciTech Connect

    Yarwood, R. R.; Rockhold, M. L.; Niemet, M. R.; Selker, John S.; Bottomley, Peter J.

    2006-10-05

    A novel analytical method was developed that permitted real-time, noninvasive measurements of microbial growth and associated changes in hydrodynamic properties in porous media under unsaturated flowing conditions. Salicylate-induced, lux gene-based bioluminescence was used to quantify the temporal and spatial development of colonization over a seven day time course. Water contents were determined daily by measuring light transmission through the system. Hydraulic flow paths were determined daily by pulsing a bromophenol blue dye solution through the colonized region of the sand. Bacterial growth and accumulation had a significant impact on the hydraulic properties of the porous media. Microbial colonization caused localized drying within the colonized zone, with decreases in saturation approaching 50% of antecedent values, and a 25% lowering of the capillary fringe height. Flow was retarded within the colonized zone and diverted around it. The apparent solute velocity through the colonized region was reduced from 0.41 cm min 1 (R2 = 0.99) to 0.25 cm min 1 (R2 = 0.99) by the sixth day of the experiment, associated with maximum population densities that would occupy about 7% of the available pore space within the colonized region. Changes in the extent of colonization occurred over the course of the experiment, including upward migration against flow. The distribution of cells was not determined by water flow alone, but rather by a dynamic interaction between water flow and microbial growth. This experimental system provides rich data sets for the testing of conceptualizations expressed through numerical modeling.

  16. Review of ground-water flow and transport models in the unsaturated zone

    SciTech Connect

    Oster, C.A.

    1982-11-01

    Models of partially saturated flow and transport in porous media have application in the analysis of existing as well as future low-level radioactive waste facilities located above the water table. An extensive literature search along with telephone and mail correspondence with recognized leading experts in the field, was conducted to identify computer models suitable for studies of low-level radioactive waste facilities located in the unsaturated zone. Fifty-five existing models were identified as potentially useful. Ten of these models were selected for further examination. This report contains a statement of the ground-water flow-contaminant transport problem, a discussion of those methods used to reduce the physical problem to a computer model, a brief discussion about the data requirements of these models. The procedure used to select the ten codes for further discussion is given, along with a list of these models. Finally, the Appendices contain the data about the fifty-five codes examined. Specifically Appendix D contains the detailed discussion of each of the ten selected codes. Included in each discussion are such items which a potential user requires in determining whether the code is suitable for his applications. Appendix E contains brief summary information about each of the fifty-five codes. Included in the summaries are identification data, authors, pertinent references, and model type.

  17. Predicting Unsaturated Zone Nitrogen Mass Balances in Agricultural Settings of the United States

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Unsaturated zone N fate and transport were evaluated at four sites to identify the predominant pathways of N cycling: an almond orchard and cornfield in the lower Merced River study basin, California (CA); and corn-soybean rotations in study basins at Maple Creek, Nebraska (NE) and at Morgan Creek, ...

  18. Gas flow to a barometric pumping well in a multilayer unsaturated zone

    NASA Astrophysics Data System (ADS)

    You, Kehua; Zhan, Hongbin; Li, Jian

    2011-05-01

    When an open well is installed in an unsaturated zone, gas can flow between the subsurface and the well depending on the gas pressure gradient near the well. This well is called a barometric pumping well (BPW). Quantifying gas flow rate to and from a BPW is indispensable to optimize the passive soil vapor extraction in remediation of volatile organic compounds in the unsaturated zone. This study presents a two-dimensional (2-D) semianalytical solution for a multilayer unsaturated zone (ML solution) to determine gas flow rate to and from a BPW. The gas flow rate is approximated by a decomposing method frequently used in previous studies, that is, first solving the one-dimensional (1-D) vertical flow equation in response to the surface barometric pressure fluctuations and then superimposing this solution on that of the 1-D horizontally radial flow equation. The error induced by this approximation is quantified by a 2-D numerical simulation for the first time in this study. Results show that the maximum error induced is 20% at the peak flow rates. The ML solution is demonstrated to be sufficient for predicting subsurface gas pressure and gas flow rate in a multilayer unsaturated zone by the barometric pumping test at the Hanford site.

  19. One Century of Unsaturated Zone Hydrology: Then, Now, But What Next?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Buckingham's 1907 paper on the movement of soil moisture is viewed by many as the foundation of unsaturated zone hydrology. Buckingham's work came at a time when most studies in soil physics focused on field soil water status, water retention, evaporation and especially the physical environment of p...

  20. An analytical solution for transient radial flow through unsaturated fractured porous media

    SciTech Connect

    Wu, Yu-Shu; Pan, Lehua

    2004-02-13

    This paper presents analytical solutions for one-dimensional radial transient flow through horizontal, unsaturated fractured rock formation. In these solutions, unsaturated flow through fractured media is described by a linearized Richards' equation, while fracture-matrix interaction is handled using the dual-continuum concept. Although linearizing Richards' equation requires a specially correlated relationship between relative permeability and capillary pressure functions for both fractures and matrix, these specially formed relative permeability and capillary pressure functions are still physically meaningful. These analytical solutions can thus be used to describe the transient behavior of unsaturated flow in fractured media under the described model conditions. They can also be useful in verifying numerical simulation results, which, as demonstrated in this paper, are otherwise difficult to validate.

  1. COLLABORATION: INTERFACIAL SOIL CHEMISTRY OF RADIONUCLIDES IN THE UNSATURATED ZONE

    EPA Science Inventory

    Mobility of radionuclides (Cs+, Sr2+) in the vadose zone is controlled by sorptive interactions with natural soil particles. Weathering of silicates and intercalation of clay minerals with hydroxy -aluminum and -aluminosilicate species under the intense geochemical conditions in...

  2. 40 CFR 264.278 - Unsaturated zone monitoring.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... background plot having characteristics similar to those of the treatment zone. (2) Background soil-pore liquid values must be based on at least quarterly sampling for one year at a background plot...

  3. Mineral carbonation in water-unsaturated porous media

    NASA Astrophysics Data System (ADS)

    Harrison, A. L.; Dipple, G. M.; Mayer, K. U.; Power, I. M.

    2014-12-01

    Ultramafic mine tailings have an untapped capacity to sequester CO2 directly from air or CO2-rich gas streams via carbonation of tailings minerals [1]. The CO2 sequestration capacity of these sites could be exploited simply by increasing the supply of CO2 into tailings, such as through circulation of air or flue gas from mine site power plants [1,2]. Mine tailings storage facilities typically have heterogeneously distributed pore water [1], affecting both the reactive capacity of the porous medium and the exposure of reactive phases to CO2 [3]. We examine the physical reaction processes that govern carbonation efficiency in variably saturated porous media using meter-scale column experiments containing the tailings mineral, brucite [Mg(OH)2], that were supplied with 10% CO2 gas streams. The experiments were instrumented with water content and gas phase CO2 sensors to track changes in water saturation and CO2concentration with time. The precipitation of hydrated Mg-carbonates as rinds encasing brucite particles resulted in passivation of brucite surfaces and an abrupt shut down of the reaction prior to completion. Moreover, the extent of reaction was further limited at low water saturation due to the lack of water available to form hydrated Mg-carbonates, which incorporate water into their crystal structures. Reactive transport modeling using MIN3P-DUSTY [4] revealed that the instantaneous reaction rate was not strongly affected by water saturation, but the reactive capacity was reduced significantly. Surface passivation and water-limited reaction resulted in a highly non-geometric evolution of reactive surface area. The extent of reaction was also limited at high water content because viscous fingering of the gas streams injected at the base of the columns resulted in narrow zones of highly carbonated material, but left a large proportion of brucite unreacted. The implication is that carbonation efficiency in mine tailings could be maximized by targeting an

  4. Pesticide fate and transport throughout unsaturated zones in five agricultural settings, USA

    USGS Publications Warehouse

    Hancock, T.C.; Sandstrom, M.W.; Vogel, J.R.; Webb, R.M.T.; Bayless, E.R.; Barbash, J.E.

    2008-01-01

    Pesticide transport through the unsaturated zone is a function of chemical and soil characteristics, application, and water recharge rate. The fate and transport of 82 pesticides and degradates were investigated at five different agricultural sites. Atrazine and metolachlor, as well as several of the degradates of atrazine, metolachlor, acetochlor, and alachlor, were frequently detected in soil water during the 2004 growing season, and degradates were generally more abundant than parent compounds. Metolachlor and atrazine were applied at a Nebraska site the same year as sampling, and focused recharge coupled with the short time since application resulted in their movement in the unsaturated zone 9 m below the surface. At other sites where the herbicides were applied 1 to 2 yr before sampling, only degradates were found in soil water. Transformations of herbicides were evident with depth and during the 4-mo sampling time and reflected the faster degradation of metolachlor oxanilic acid and persistence of metolachor ethanesulfonic acid. The fraction of metolachlor ethanesulfonic acid relative to metolachlor and metolachlor oxanilic acid increased from 0.3 to > 0.9 at a site in Maryland where the unsaturated zone was 5 m deep and from 0.3 to 0.5 at the shallowest depth. The flux of pesticide degradates from the deepest sites to the shallow ground water was greatest (3.0–4.9 μmol m−2 yr−1) where upland recharge or focused flow moved the most water through the unsaturated zone. Flux estimates based on estimated recharge rates and measured concentrations were in agreement with fluxes estimated using an unsaturated-zone computer model (LEACHM).

  5. Pesticide fate and transport throughout unsaturated zones in five agricultural settings, USA.

    PubMed

    Hancock, Tracy C; Sandstrom, Mark W; Vogel, Jason R; Webb, Richard M T; Bayless, E Randall; Barbash, Jack E

    2008-01-01

    Pesticide transport through the unsaturated zone is a function of chemical and soil characteristics, application, and water recharge rate. The fate and transport of 82 pesticides and degradates were investigated at five different agricultural sites. Atrazine and metolachlor, as well as several of the degradates of atrazine, metolachlor, acetochlor, and alachlor, were frequently detected in soil water during the 2004 growing season, and degradates were generally more abundant than parent compounds. Metolachlor and atrazine were applied at a Nebraska site the same year as sampling, and focused recharge coupled with the short time since application resulted in their movement in the unsaturated zone 9 m below the surface. At other sites where the herbicides were applied 1 to 2 yr before sampling, only degradates were found in soil water. Transformations of herbicides were evident with depth and during the 4-mo sampling time and reflected the faster degradation of metolachlor oxanilic acid and persistence of metolachor ethanesulfonic acid. The fraction of metolachlor ethanesulfonic acid relative to metolachlor and metolachlor oxanilic acid increased from 0.3 to >0.9 at a site in Maryland where the unsaturated zone was 5 m deep and from 0.3 to 0.5 at the shallowest depth. The flux of pesticide degradates from the deepest sites to the shallow ground water was greatest (3.0-4.9 micromol m(-2) yr(-1)) where upland recharge or focused flow moved the most water through the unsaturated zone. Flux estimates based on estimated recharge rates and measured concentrations were in agreement with fluxes estimated using an unsaturated-zone computer model (LEACHM). PMID:18453430

  6. Contaminant Transport in the Unsaturated Zone Theory and Modeling

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Mathematical models are increasingly used to better understand and quantify site-specific subsurface water flow and solute transport processes. This chapter reviews mathematical models for solute transport in predominantly variably-saturated media. After a brief description of the physics and mathe...

  7. Hydrochemical investigations in characterizing the unsaturated zone at Yucca Mountain, Nevada

    SciTech Connect

    Yang, I.C.; Rattray, G.W.; Ferarese, J.S.; Yu, P.; Ryan, J.N.

    1998-11-01

    Hydrochemical and isotopic investigations of ground water at Yucca Mountain, Nevada, site of a potential permanent national nuclear-waste repository, demonstrate that younger rocks are dominated by calcium-sulfate or calcium-chloride water and that older rocks contain sodium-carbonate or sodium-bicarbonate water. Furthermore, unsaturated-zone pore water has significantly larger concentrations of major ions and dissolved solids than does the saturated-zone water. Recharge of perched or saturated-zone water, therefore, requires rapid flow through fractures or permeable regions in the unsaturated zone to avoid mixing with the chemically concentrated water in the unsaturated zone. This conceptual model is consistent with observations of rapidly moved post-bomb (post-1954) tritium and chlorine-36 in the deep unsaturated zone at Yucca Mountain. Presence of post-bomb tritium in matrix water away from fracture zones further indicates that parts of the fast-flow water that moves through fractures have been diverted laterally into nonwelded units. Experimental data show that different lithologic units require specific water-extraction methods for stable-isotope analyses of hydrogen and oxygen to ensure accurate characterization. Vacuum-distillation and compression-extraction methods both can yield accurate data but must be used with specific lithologies. Column experiments demonstrate that percolating water can exchange with pore water of the core as well as water held in zeolite minerals in the core. Exchange rates range from days to months. Pore-water samples from core, therefore, reflect the most recently infiltrated water but do not reflect percolating water of the distant past.

  8. Desiccation of unsaturated porous media: Intermediate-scale experiments and numerical simulation

    SciTech Connect

    Oostrom, Martinus; Wietsma, Thomas W.; Dane, J. H.; Truex, Michael J.; Ward, Anderson L.

    2009-08-01

    Soil desiccation (drying) is recognized as a potentially robust vadose zone remediation process involving water evaporation induced by air injection and extraction. Desiccation has the potential to immobilize contaminants and could potentially improve access for other gas-phase treatments by reducing water saturation and therefore increasing sediment gas-phase permeability. Before this technology could be deployed in the field, concerns related to energy limitations, osmotic effects, and potential contaminant remobilization after rewetting need to be addressed. A series of detailed wedge-shaped, intermediate-scale laboratory experiments in unsaturated homogeneous and simple heterogeneous systems was conducted to improve the understanding of the impact of energy balance issues on soil desiccation. The experiments were simulated with the multifluid flow simulator STOMP, using independently obtained hydraulic and thermal porous medium properties. In all the experiments, the injection of dry air proved to be an effective means for removing essentially all moisture from the test media. Evaporative cooling was observed which generally decreased with increased distance from the gas inlet chamber. Observations of temperature in fine-grained sands in the heterogeneous systems show two local temperature minima associated with the cooling. The first one occurs because of evaporation in the adjacent medium-grained sand whereas the second minimum is attributed to evaporative cooling in the fine-grained sand itself. Results of the laboratory tests were simulated accurately when thermal properties of the flow cell walls and insulation material were taken into account, indicating that the proper physics were incorporated into the simulator.

  9. Multimodel analysis of anisotropic diffusive tracer-gas transport in a deep arid unsaturated zone

    NASA Astrophysics Data System (ADS)

    Green, Christopher T.; Walvoord, Michelle A.; Andraski, Brian J.; Striegl, Robert G.; Stonestrom, David A.

    2015-08-01

    Gas transport in the unsaturated zone affects contaminant flux and remediation, interpretation of groundwater travel times from atmospheric tracers, and mass budgets of environmentally important gases. Although unsaturated zone transport of gases is commonly treated as dominated by diffusion, the characteristics of transport in deep layered sediments remain uncertain. In this study, we use a multimodel approach to analyze results of a gas-tracer (SF6) test to clarify characteristics of gas transport in deep unsaturated alluvium. Thirty-five separate models with distinct diffusivity structures were calibrated to the tracer-test data and were compared on the basis of Akaike Information Criteria estimates of posterior model probability. Models included analytical and numerical solutions. Analytical models provided estimates of bulk-scale apparent diffusivities at the scale of tens of meters. Numerical models provided information on local-scale diffusivities and feasible lithological features producing the observed tracer breakthrough curves. The combined approaches indicate significant anisotropy of bulk-scale diffusivity, likely associated with high-diffusivity layers. Both approaches indicated that diffusivities in some intervals were greater than expected from standard models relating porosity to diffusivity. High apparent diffusivities and anisotropic diffusivity structures were consistent with previous observations at the study site of rapid lateral transport and limited vertical spreading of gas-phase contaminants. Additional processes such as advective oscillations may be involved. These results indicate that gases in deep, layered unsaturated zone sediments can spread laterally more quickly, and produce higher peak concentrations, than predicted by homogeneous, isotropic diffusion models.

  10. Performance assessment model development and analysis of radionuclide transport in the unsaturated zone, Yucca Mountain, Nevada.

    PubMed

    Robinson, Bruce A; Li, Chunhong; Ho, Clifford K

    2003-01-01

    This paper describes the development and use of a particle-tracking model to perform radionuclide-transport simulations in the unsaturated zone at Yucca Mountain, Nevada. The goal of the effort was to produce a computational model that can be coupled to the project's calibrated 3D site-scale flow model so that the results of that effort could be incorporated directly into the Total System Performance Assessment (TSPA) analyses. The transport model simulates multiple species (typically 20 or more) with complex time-varying and spatially varying releases from the potential repository. Water-table rise, climate-change scenarios, and decay chains are additional features of the model. A cell-based particle-tracking method was employed that includes a dual-permeability formulation, advection, longitudinal dispersion, matrix diffusion, and colloid-facilitated transport. This paper examines the transport behavior of several key radionuclides through the unsaturated zone using the calibrated 3D unsaturated flow fields. Computational results illustrate the relative importance of fracture flow, matrix diffusion, and lateral diversion on the distribution of travel times from the simulated repository to the water table for various climatic conditions. Results also indicate rapid transport through fractures for a portion of the released mass. Further refinement of the model will address several issues, including conservatism in the transport model, the assignment of parameters in the flow and transport models, and the underlying assumptions used to support the conceptual models of flow and transport in the unsaturated zone at Yucca Mountain. PMID:12714294

  11. Multimodel analysis of anisotropic diffusive tracer-gas transport in a deep arid unsaturated zone

    USGS Publications Warehouse

    Green, Christopher T.; Walvoord, Michelle Ann; Andraski, Brian J.; Striegl, Rob; Stonestrom, David A.

    2015-01-01

    Gas transport in the unsaturated zone affects contaminant flux and remediation, interpretation of groundwater travel times from atmospheric tracers, and mass budgets of environmentally important gases. Although unsaturated zone transport of gases is commonly treated as dominated by diffusion, the characteristics of transport in deep layered sediments remain uncertain. In this study, we use a multimodel approach to analyze results of a gas-tracer (SF6) test to clarify characteristics of gas transport in deep unsaturated alluvium. Thirty-five separate models with distinct diffusivity structures were calibrated to the tracer-test data and were compared on the basis of Akaike Information Criteria estimates of posterior model probability. Models included analytical and numerical solutions. Analytical models provided estimates of bulk-scale apparent diffusivities at the scale of tens of meters. Numerical models provided information on local-scale diffusivities and feasible lithological features producing the observed tracer breakthrough curves. The combined approaches indicate significant anisotropy of bulk-scale diffusivity, likely associated with high-diffusivity layers. Both approaches indicated that diffusivities in some intervals were greater than expected from standard models relating porosity to diffusivity. High apparent diffusivities and anisotropic diffusivity structures were consistent with previous observations at the study site of rapid lateral transport and limited vertical spreading of gas-phase contaminants. Additional processes such as advective oscillations may be involved. These results indicate that gases in deep, layered unsaturated zone sediments can spread laterally more quickly, and produce higher peak concentrations, than predicted by homogeneous, isotropic diffusion models.

  12. Simulated fate and transport of metolachlor in the unsaturated zone, Maryland, USA

    USGS Publications Warehouse

    Bayless, E.R.; Capel, P.D.; Barbash, J.E.; Webb, R.M.T.; Hancock, T.L.C.; Lampe, D.C.

    2008-01-01

    An unsaturated-zone transport model was used to examine the transport and fate of metolachlor applied to an agricultural site in Maryland, USA. The study site was instrumented to collect data on soil-water content, soil-water potential, ground water levels, major ions, pesticides, and nutrients from the unsaturated zone during 2002-2004. The data set was enhanced with site-specific information describing weather, soils, and agricultural practices. The Root Zone Water Quality Model was used to simulate physical, chemical, and biological processes occurring in the unsaturated zone. Model calibration to bromide tracer concentrations indicated flow occurred through the soil matix. Simulated recharge rates were within the measured range of values. The pesticide transport model was calibrated to the intensive data collection period (2002-2004), and the calibrated model was then used to simulate the period 1984 through 2004 to examine the impact of sustained agricultural management practices on the concentrations of metolachlor and its degradates at the study site. Simulation results indicated that metolachlor degrades rapidly in the root zone but that the degradates are transported to depth in measurable quantities. Simulations indicated that degradate transport is strongly related to the duration of sustained use of metolachlor and the extent of biodegradation. 

  13. Geologic character of tuffs in the unsaturated zone at Yucca Mountain, southern Nevada

    SciTech Connect

    Scott, R.B.; Spengler, R.W.; Diehl, S.; Lappin, A.R.; Chornack, M.P.

    1982-12-31

    At Yucca Mountain, a potential site for a high-level nuclear waste repository on the Nevada Test Site in southern Nevada, evaluation of the geologic setting and rock physical properties, along with previous regional hydrologic studies, has provided background that can be used for construction of a preliminary conceptual hydrologic model of the unsaturated zone. The 500-m-thick unsaturated portion of Yucca Mountain consists of alternating layers of two contrasting types of tuff. One type consists of highly fractured, densely welded, relatively nonporous but highly transmissive ash-flow tuffs. The other type consists of relatively unfractured, nonwelded, highly porous but relatively nontransmissive, argillic and zeolitic bedded tuffs and ash-flow tuffs. The contrast between these two sets of distinctive physical properties results in a stratified sequence best described as "physical-property stratigraphy" as opposed to traditional petrologic stratigraphy of volcanic rocks. The vast majority of recharge through the unsaturated zone is assumed to be vertical; the dominant migration may occur in fractures of densely welded tuffs and in the matrix of nonwelded tuff, but the mode of fluid flow in these unsaturated systems is undetermined. Limited lateral flow of recharge may occur at horizons where local perched water tables may exist above relatively nontransmissive zeolitized nonwelded tuffs. The pervasive north-northwest-striking fractures may control the direction of lateral flow of recharge, if any, in the unsaturated zone, and certainly that direction coincides closely with the observed southeasterly flow direction in the saturated zone under Yucca Mountain. Empirical evaluation of this conceptual hydrologic model has begun. 41 refs., 18 figs., 2 tabs.

  14. Consequences of varied soil hydraulic and meteorological complexity on unsaturated zone time lag estimates.

    PubMed

    Vero, S E; Ibrahim, T G; Creamer, R E; Grant, J; Healy, M G; Henry, T; Kramers, G; Richards, K G; Fenton, O

    2014-12-01

    The true efficacy of a programme of agricultural mitigation measures within a catchment to improve water quality can be determined only after a certain hydrologic time lag period (subsequent to implementation) has elapsed. As the biophysical response to policy is not synchronous, accurate estimates of total time lag (unsaturated and saturated) become critical to manage the expectations of policy makers. The estimation of the vertical unsaturated zone component of time lag is vital as it indicates early trends (initial breakthrough), bulk (centre of mass) and total (Exit) travel times. Typically, estimation of time lag through the unsaturated zone is poor, due to the lack of site specific soil physical data, or by assuming saturated conditions. Numerical models (e.g. Hydrus 1D) enable estimates of time lag with varied levels of input data. The current study examines the consequences of varied soil hydraulic and meteorological complexity on unsaturated zone time lag estimates using simulated and actual soil profiles. Results indicated that: greater temporal resolution (from daily to hourly) of meteorological data was more critical as the saturated hydraulic conductivity of the soil decreased; high clay content soils failed to converge reflecting prevalence of lateral component as a contaminant pathway; elucidation of soil hydraulic properties was influenced by the complexity of soil physical data employed (textural menu, ROSETTA, full and partial soil water characteristic curves), which consequently affected time lag ranges; as the importance of the unsaturated zone increases with respect to total travel times the requirements for high complexity/resolution input data become greater. The methodology presented herein demonstrates that decisions made regarding input data and landscape position will have consequences for the estimated range of vertical travel times. Insufficiencies or inaccuracies regarding such input data can therefore mislead policy makers regarding

  15. Thermal history of the unsaturated zone at Yucca Mountain, Nevada, USA

    USGS Publications Warehouse

    Whelan, J.F.; Neymark, L.A.; Moscati, R.J.; Marshall, B.D.; Roedder, E.

    2008-01-01

    Secondary calcite, silica and minor amounts of fluorite deposited in fractures and cavities record the chemistry, temperatures, and timing of past fluid movement in the unsaturated zone at Yucca Mountain, Nevada, the proposed site of a high-level radioactive waste repository. The distribution and geochemistry of these deposits are consistent with low-temperature precipitation from meteoric waters that infiltrated at the surface and percolated down through the unsaturated zone. However, the discovery of fluid inclusions in calcite with homogenization temperatures (Th) up to ???80 ??C was construed by some scientists as strong evidence for hydrothermal deposition. This paper reports the results of investigations to test the hypothesis of hydrothermal deposition and to determine the temperature and timing of secondary mineral deposition. Mineral precipitation temperatures in the unsaturated zone are estimated from calcite- and fluorite-hosted fluid inclusions and calcite ??18O values, and depositional timing is constrained by the 207Pb/235U ages of chalcedony or opal in the deposits. Fluid inclusion Th from 50 samples of calcite and four samples of fluorite range from ???35 to ???90 ??C. Calcite ??18O values range from ???0 to ???22??? (SMOW) but most fall between 12 and 20???. The highest Th and the lowest ??18O values are found in the older calcite. Calcite Th and ??18O values indicate that most calcite precipitated from water with ??18O values between -13 and -7???, similar to modern meteoric waters. Twenty-two 207Pb/235U ages of chalcedony or opal that generally postdate elevated depositional temperatures range from ???9.5 to 1.9 Ma. New and published 207Pb/235U and 230Th/Uages coupled with the Th values and estimates of temperature from calcite ??18O values indicate that maximum unsaturated zone temperatures probably predate ???10 Ma and that the unsaturated zone had cooled to near-present-day temperatures (24-26 ??C at a depth of 250 m) by 2-4 Ma. The evidence

  16. Nitrogen transport and transformation in the saturated-unsaturated zone under recharge, runoff, and discharge conditions.

    PubMed

    Ma, Zhifei; Lian, Xinying; Jiang, Yonghai; Meng, Fanhua; Xi, Beidou; Yang, Yu; Yuan, Zhiye; Xu, Xiangjian

    2016-05-01

    Water level (WL) changes are an important factor in the fate and transport of nitrogen in the saturated-unsaturated zone. In this study, the fate of nitrogen was investigated under simulated conditions of replenishment, runoff, and discharge. Three patterns of water level changes of ascent, stability, and descent were simulated under laboratory conditions to study nitrogen transport and transformation. Three columns (I, II, and III) were used to simulate the conditions of replenishment, steady water level, and discharge, respectively. The nitrate-nitrogen (NO3 (-)-N), nitrite-nitrogen (NO2 (-)-N), and ammonia-nitrogen (NH4 (+)-N) concentrations observed at different depths were compared among the three columns at 46.5 and 251.5 h. The results indicated that the NO3 (-)-N concentration decreased with time in both the saturated and unsaturated zones of the three columns (columns I, II, and III). The maximum decreasing concentrations of NO3 (-)-N in the three columns were 14.3, 37.97, and 38.17 mg/L, respectively. However, NH4 (+)-N in the saturated zone increased with time, whereas the NH4 (+)-N concentration decreased in both the saturated and unsaturated zones of other columns. No significant change in NO2 (-)-N concentration was observed in the experiment. These results suggest that water level changes must be considered in the remediation of groundwater nitrate pollution in the field. PMID:26805922

  17. Infiltration and drainage in the unsaturated zone: comparison of numerical simulations to a monitored field experiment

    NASA Astrophysics Data System (ADS)

    Papafotiou, Alexandros; Ganz, Christina; Altfelder, Sven; Noell, Ursula; Neuweiler, Insa

    2010-05-01

    The unsaturated zone has a prominent role for groundwater resources, as it controls through flow and transport any mass exchange between atmosphere and groundwater. However, providing reliable predictions for the unsaturated zone is very demanding, as it is dominated by complex two-phase flow processes that produce high uncertainty with respect to the hydraulic properties. When modeling unsaturated flow, the typically unknown spatial distribution of hydraulic properties in the soil constitutes a primary source of uncertainty. Even if information on the exact distribution is known, additional uncertainty may stem from the non-uniqueness of the hydraulic properties, most profoundly expressed through hysteresis in the capillary pressure-saturation relationship, also known as water retention curve. In this work, we present modeling considerations for predicting an infiltration and drainage event in the unsaturated zone during a field experiment. The experiment was performed by infiltrating brilliant-blue solution while monitoring the plume movement with ERT. After the completion of infiltration (and the consequent drainage), the upper 1 meter of the soil was excavated in slices to obtain the 3D distribution of water saturation and pressure. Numerical simulations are carried out with a two-phase flow model. The results illustrate possibilities and limitations of predicting such flow processes based on the experimental information available. We demonstrate the influence and significance of hysteresis by comparing experimental findings with model runs that explicitly consider wetting and drying conditions in the experiment. Our approach allows us to identify key processes that have to be accounted for. In a feedback loop with the design of future experiments we aim at improving input specifications necessary for reliable predictive modeling of unsaturated flow.

  18. CO2 dynamics in the Amargosa Desert: Fluxes and isotopic speciation in a deep unsaturated zone

    USGS Publications Warehouse

    Walvoord, M.A.; Striegl, R.G.; Prudic, D.E.; Stonestrom, D.A.

    2005-01-01

    Natural unsaturated-zone gas profiles at the U.S. Geological Survey's Amargosa Desert Research Site, near Beatty, Nevada, reveal the presence of two physically and isotopically distinct CO2 sources, one shallow and one deep. The shallow source derives from seasonally variable autotrophic and heterotrophic respiration in the root zone. Scanning electron micrograph results indicate that at least part of the deep CO2 source is associated with calcite precipitation at the 110-m-deep water table. We use a geochemical gas-diffusion model to explore processes of CO2 production and behavior in the unsaturated zone. The individual isotopic species 12CO2, 13CO2, and 14CO2 are treated as separate chemical components that diffuse and react independently. Steady state model solutions, constrained by the measured PCO2 ??13C (in CO2), and ??14C (in CO2) profiles, indicate that the shallow CO2 source from root and microbial respiration composes ???97% of the annual average total CO2 production at this arid site. Despite the small contribution from deep CO2 production amounting to ???0.1 mol m-2 yr-1, upward diffusion from depth strongly influences the distribution of CO2 and carbon isotopes in the deep unsaturated zone. In addition to diffusion from deep CO2 production, 14C exchange with a sorbed CO2 phase is indicated by the modeled ??14C profiles, confirming previous work. The new model of carbon-isotopic profiles provides a quantitative approach for evaluating fluxes of carbon under natural conditions in deep unsaturated zones.

  19. Moisture Content and Migration Dynamics in Unsaturated Porous Media

    NASA Technical Reports Server (NTRS)

    Homsy, G. M.

    1993-01-01

    Fundamental studies of fluid mechanics and transport in partially saturated soils are presented. Solution of transient diffusion problems in support of the development of probes for the in-situ measurement of moisture content is given. Numerical and analytical methods are used to study the fundamental problem of meniscus and saturation front propagation in geometric models of porous media.

  20. A numerical approach for groundwater flow in unsaturated porous media

    NASA Astrophysics Data System (ADS)

    Quintana, F.; Guarracino, L.; Saliba, R.

    2006-07-01

    In this article, a computational tool to simulate groundwater flow in variably saturated non-deformable fractured porous media is presented, which includes a conceptual model to obtain analytical expressions of water retention and hydraulic conductivity curves for fractured hard rocks and a numerical algorithm to solve the Richards equation. To calculate effective saturation and relative hydraulic conductivity curves we adopt the Brooks-Corey model assuming fractal laws for both aperture and number of fractures. A standard Galerkin formulation was employed to solve the Richards' equation together with a Crank-Nicholson scheme with Richardson extrapolation for the time discretization.The main contribution of this paper is to group an analytical model of the authors with a robust numerical algorithm designed to solve adequately the highly non-linear Richards' equation generating a tool for porous media engineering.

  1. Ground water age and nitrate distribution within a glacial aquifer beneath a thick unsaturated zone

    USGS Publications Warehouse

    Johnston, C.T.; Cook, P.G.; Frape, S.K.; Plummer, L.N.; Busenberg, E.; Blackport, R.J.

    1998-01-01

    The impact on ground water quality from increasing fertilizer application rates over the past 40 years is evaluated within a glacial aquifer system beneath a thick unsaturated zone. Ground water ages within the aquifer could not be accurately determined from the measured distribution of 3H and as a result, chlorofluorocarbon (CFC) and 3H/3He dating techniques were applied. Beneath a 25 m thick unsaturated zone, ground water ages based on CFC-11 concentrations were greater than 3H/3He ground water ages by 6 to 10 years, due to the time lag associated with the diffusion of CFCs through the unsaturated zone. Using the corrected CFC-11 and 3H/3He ground water ages and the estimated travel time of 3H within the unsaturated zone, the approximate position of ground water recharged since the mid-1960s was determined. Nitrate concentrations within post mid-1960s recharge were generally elevated and near or above the drinking water limit of 10 mg-N/L. In comparison, pre mid-1960s recharge had nitrate concentrations <2.5 mg-N/L. The elevated NO3- concentrations in post mid-1960s recharge are attributed mainly to increasing fertilizer application rates between 1970 and the mid- to late 1980s. Anaerobic conditions suitable for denitrification are present within pre mid-1960s recharge indicating that removal of DO is a slow process taking tens of years. Over the next 10 to 20 years, nitrate concentrations at municipal well fields that are currently capturing aerobic ground water recharged near the mid-1960s are expected to increase because of the higher fertilizer application rates beginning in the 1970s and 1980s.The impact on ground water quality from increasing fertilizer application rates over the past 40 years is evaluated within a glacial aquifer system beneath a thick unsaturated zone. Beneath a 25 m thick unsaturated zone, ground water ages based on CFC-11 concentrations were greater than 3H/3He ground water ages by 6 to 10 years, due to the time lag associated with the

  2. Porosity and permeability of tuffs from the unsaturated zone at Yucca Mountain, Nevada

    SciTech Connect

    Soeder, D.J.; Dishart, J.E. )

    1992-01-01

    An investigation of the intrinsic flow properties of the rock matrix in the unsaturated zone at Yucca Mountain, Nevada, was carried out by performing single-phase water or air permeability measurements on about 150 selected samples representing all of the different rock units in the unsaturated zone. Pores were studied by examining thin sections of samples impregnated with fluorescent-dyed epoxy. Yucca Mountain is made up of volcanic tuff, which occurs in three distinct textures: welded, nonwelded, and bedded. Welded tuffs occur in two thick, rhyolitic, pyroclastic flow units. In thin sections, the typical welded-tuff pore structure appears to consist of isolated voids interconnected by microfractures. Porosities average about 10 percent, and matrix permeabilities are generally 1 microdarcy or less. The nonwelded tuffs occur in several thin pyroclastic flows between and below the two main welded units. Porosities average about 20 to 30%, and permeabilities are in the microdarcy to millidarcy range. The nonwelded tuffs appear in thin sections to have an open, well-interconnected pore system with significant intragranular porosity in pumice and lithic grains. These tuffs often contain various amounts of secondary clay and zeolite minerals in the pores, which may account for the wide range in permeabilities. The bedded tuffs consist of friable, low-density volcanic ash with porosities of 50% or more and permeabilities often above 1 darcy. These tuffs are the most porous and permeable rock units in the unsaturated zone, and contain large intergranular pores and significant intragranular porosity in frothy pumice clasts. Results of this investigation will help improve the understanding of groundwater movement through the unsaturated zone.

  3. Effect of grain-coating mineralogy on nitrate and sulfate storage in the unsaturated zone

    USGS Publications Warehouse

    Reilly, T.J.; Fishman, N.S.; Baehr, A.L.

    2009-01-01

    Unsaturated-zone sediments and the chemistry of shallow groundwater underlying a small (???8-km2) watershed were studied to identify the mechanisms responsible for anion storage within the Miocene Bridgeton Formation and weathered Coastal Plain deposits in southern New Jersey. Lower unsaturated-zone sediments and shallow groundwater samples were collected and concentrations of selected ions (including NO3- and SO42-) from 11 locations were determined. Grain size, sorting, and color of the lower unsaturated-zone sediments were determined and the mineralogy of these grains and the composition of coatings were analyzed by petrographic examination, scanning electron microscopy and energy dispersive analysis of x-rays, and quantitative whole-rock x-ray diffraction. The sediment grains, largely quartz and chert (80-94% w/w), are coated with a very fine-grained (<20 ??m), complex mixture of kaolinite, halloysite, goethite, and possibly gibbsite and lepidocrocite. The mineral coatings are present as an open fabric, resulting in a large surface area in contact with pore water. Significant correlations between the amount of goethite in the grain coatings and the concentration of sediment-bound SO42- were observed, indicative of anion sorption. Other mineral-chemical relations indicate that negatively charged surfaces and competition with SO 42- results in exclusion of NO3- from inner sphere exchange sites. The observed NO3- storage may be a result of matrix forces within the grain coatings and outer sphere complexation. The results of this study indicate that the mineralogy of grain coatings can have demonstrable effects on the storage of NO 3- and SO42- in the unsaturated zone. ?? Soil Science Society of America. All rights reserved.

  4. Collboration: Interfacial Soil Chemistry of Radionuclides in the Unsaturated Zone

    SciTech Connect

    Karl T. Mueller; Don Chorover; Peggy O'Day; R. Jeff Serne; Garry Crosson; Geoffrey Bowers; Nelson Rivera

    2006-12-11

    The principal goal of this project was to assess the molecular nature and stability of radionuclide immoblization during weathering reactions in bulk Hanford sediments and their high surface area clay mineral constituents. We focused on the unique aqueous geochemical conditions that are representative of waste-impacted locations in the Hanford site vadose zone; high ionic strength, high pH and high Al concentrations. The specific objectives of the work were to measure the coupling of clay mineral weathering and contaminant uptake kinetics of Cs, Sr and I; determine the molecular structure of contaminant binding sites and their change with weathering time during and after exposure to synthetic tank waste leachate; establish the stability of neoformed weathering products and their sequestered contaminbants upon exposure of the solids to more natural soil solutaions afer remofal of the caustic waste source; and integrate macroscopic, microscopic and spectroscopic data to distinguish labile from non-labile contaminant binding environments, including their dependence on system composition and weathering time.

  5. Nitrogen fluxes through unsaturated zones in five agricultural settings across the USA

    NASA Astrophysics Data System (ADS)

    Green, C. T.; Fisher, L. H.; Bekins, B. A.

    2006-12-01

    The main controls on nitrogen (N) fluxes between the root zone and the water table were determined for agricultural sites in California, Washington, Nebraska, Indiana, and Maryland in 2004 and 2005. Sites included irrigated and non-irrigated fields; soil textures ranging from clay to sand; crops including corn, soybeans, almonds, and pasture; and unsaturated zone thicknesses ranging from 0.5 to 20 m. Chemical analyses of water from lysimeters, shallow wells, and sediment cores indicate that advective transport of nitrate is the dominant process affecting the rate of N transport below the root zone. Vertical profiles of (1) N species, (2) stable N and O isotopes, and (3) oxygen gas in unsaturated zone air and shallow ground water, and correlations between N and other agricultural chemicals indicate that reactions do not greatly affect N concentrations between the root zone and the capillary fringe. Relatively stable concentrations at depths greater than a few meters allow calculation of nitrogen fluxes to the saturated zone. These fluxes are equivalent to 14 - 64% of the N application rates. At the same locations, median vertical fluxes of N in ground water are generally lower, ranging from 4 - 37% of N application rates. The lower nitrate fluxes in ground water reflect processes including lateral flow to tile drains and denitrification in the capillary fringe, as well as historical changes in N inputs.

  6. Land-use classes to characterize watersheds and unsaturated zones in North Carolina

    USGS Publications Warehouse

    Terziotti, Silvia; Eimers, Jo Leslie

    2001-01-01

    This web site contains the Federal Geographic Data Committee-compliant metadata (documentation) for digital data produced for the North Carolina, Department of Environment and Natural Resources, Public Water Supply Section, Source Water Assessment Program. The metadata are for 11 individual Geographic Information System data sets. An overlay and indexing method was used with the data to derive a rating for unsaturated zone and watershed characteristics for use by the State of North Carolina in assessing more than 11,000 public water-supply wells and approximately 245 public surface-water intakes for susceptibility to contamination. For ground-water supplies, the digital data sets used in the assessment included unsaturated zone rating, vertical series hydraulic conductance, land-surface slope, and land cover. For assessment of public surface-water intakes, the data sets included watershed characteristics rating, average annual precipitation, land-surface slope, land cover, and ground-water contribution. Documentation for the land-use data set applies to both the unsaturated zone and watershed characteristics ratings. Documentation for the estimated depth-to-water map used in the calculation of the vertical series hydraulic conductance also is included.

  7. Percent-slope classes to characterize the unsaturated zone in North Carolina

    USGS Publications Warehouse

    Terziotti, Silvia; Eimers, Jo Leslie

    2001-01-01

    This web site contains the Federal Geographic Data Committee-compliant metadata (documentation) for digital data produced for the North Carolina, Department of Environment and Natural Resources, Public Water Supply Section, Source Water Assessment Program. The metadata are for 11 individual Geographic Information System data sets. An overlay and indexing method was used with the data to derive a rating for unsaturated zone and watershed characteristics for use by the State of North Carolina in assessing more than 11,000 public water-supply wells and approximately 245 public surface-water intakes for susceptibility to contamination. For ground-water supplies, the digital data sets used in the assessment included unsaturated zone rating, vertical series hydraulic conductance, land-surface slope, and land cover. For assessment of public surface-water intakes, the data sets included watershed characteristics rating, average annual precipitation, land-surface slope, land cover, and ground-water contribution. Documentation for the land-use data set applies to both the unsaturated zone and watershed characteristics ratings. Documentation for the estimated depth-to-water map used in the calculation of the vertical series hydraulic conductance also is included.

  8. Land-cover classes to characterize the unsaturated zone in North Carolina

    USGS Publications Warehouse

    Terziotti, Silvia; Eimers, Jo Leslie

    2001-01-01

    This web site contains the Federal Geographic Data Committee-compliant metadata (documentation) for digital data produced for the North Carolina, Department of Environment and Natural Resources, Public Water Supply Section, Source Water Assessment Program. The metadata are for 11 individual Geographic Information System data sets. An overlay and indexing method was used with the data to derive a rating for unsaturated zone and watershed characteristics for use by the State of North Carolina in assessing more than 11,000 public water-supply wells and approximately 245 public surface-water intakes for susceptibility to contamination. For ground-water supplies, the digital data sets used in the assessment included unsaturated zone rating, vertical series hydraulic conductance, land-surface slope, and land cover. For assessment of public surface-water intakes, the data sets included watershed characteristics rating, average annual precipitation, land-surface slope, land cover, and ground-water contribution. Documentation for the land-use data set applies to both the unsaturated zone and watershed characteristics ratings. Documentation for the estimated depth-to-water map used in the calculation of the vertical series hydraulic conductance also is included.

  9. Limited denitrification in glacial deposit aquifers having thick unsaturated zones (Long Island, USA)

    USGS Publications Warehouse

    Young, Caitlin; Kroeger, Kevin D.; Hanson, Gilbert

    2013-01-01

    The goal of this study was to demonstrate how the extent of denitrification, which is indirectly related to dissolved organ carbon and directly related to oxygen concentrations, can also be linked to unsaturated-zone thickness, a mappable aquifer property. Groundwater from public supply and monitoring wells in Northport on Long Island, New York state (USA), were analyzed for denitrification reaction progress using dissolved N2/Ar concentrations by membrane inlet mass spectrometry. This technique allows for discernment of small amounts of excess N2, attributable to denitrification. Results show an average 15 % of total nitrogen in the system was denitrified, significantly lower than model predictions of 35 % denitrification. The minimal denitrification is due to low dissolved organic carbon (29.3–41.1 μmol L−1) and high dissolved oxygen concentrations (58–100 % oxygen saturation) in glacial sediments with minimal solid-phase electron donors to drive denitrification. A mechanism is proposed that combines two known processes for aquifer re-aeration in unconsolidated sands with thick (>10 m) unsaturated zones. First, advective flux provides 50 % freshening of pore space oxygen in the upper 2 m due to barometric pressure changes. Then, oxygen diffusion across the water-table boundary occurs due to high volumetric air content in the unsaturated-zone catchment area.

  10. Limited denitrification in glacial deposit aquifers having thick unsaturated zones (Long Island, USA)

    NASA Astrophysics Data System (ADS)

    Young, Caitlin; Kroeger, Kevin D.; Hanson, Gilbert

    2013-12-01

    The goal of this study was to demonstrate how the extent of denitrification, which is indirectly related to dissolved organ carbon and directly related to oxygen concentrations, can also be linked to unsaturated-zone thickness, a mappable aquifer property. Groundwater from public supply and monitoring wells in Northport on Long Island, New York state (USA), were analyzed for denitrification reaction progress using dissolved N2/Ar concentrations by membrane inlet mass spectrometry. This technique allows for discernment of small amounts of excess N2, attributable to denitrification. Results show an average 15 % of total nitrogen in the system was denitrified, significantly lower than model predictions of 35 % denitrification. The minimal denitrification is due to low dissolved organic carbon (29.3-41.1 μmol L-1) and high dissolved oxygen concentrations (58-100 % oxygen saturation) in glacial sediments with minimal solid-phase electron donors to drive denitrification. A mechanism is proposed that combines two known processes for aquifer re-aeration in unconsolidated sands with thick (>10 m) unsaturated zones. First, advective flux provides 50 % freshening of pore space oxygen in the upper 2 m due to barometric pressure changes. Then, oxygen diffusion across the water-table boundary occurs due to high volumetric air content in the unsaturated-zone catchment area.

  11. Hydrogeology of the unsaturated zone, North Ramp area of the Exploratory Studies Facility, Yucca Mountain, Nevada

    SciTech Connect

    Rousseau, J.P.; Kwicklis, E.M.; Gillies, D.C.

    1999-03-01

    Yucca Mountain, in southern Nevada, is being investigated by the US Department of Energy as a potential site for a repository for high-level radioactive waste. This report documents the results of surface-based geologic, pneumatic, hydrologic, and geochemical studies conducted during 1992 to 1996 by the US Geological Survey in the vicinity of the North Ramp of the Exploratory Studies Facility (ESF) that are pertinent to understanding multiphase fluid flow within the deep unsaturated zone. Detailed stratigraphic and structural characteristics of the study area provided the hydrogeologic framework for these investigations. Shallow infiltration is not discussed in detail in this report because the focus in on three major aspects of the deep unsaturated-zone system: geologic framework, the gaseous-phase system, and the aqueous-phase system. However, because the relation between shallow infiltration and deep percolation is important to an overall understanding of the unsaturated-zone flow system, a summary of infiltration studies conducted to date at Yucca Mountain is provided in the section titled Shallow Infiltration. This report describes results of several Site Characterization Plan studies that were ongoing at the time excavation of the ESF North Ramp began and that continued as excavation proceeded.

  12. Preferential dealkylation reactions of s-triazine herbicides in the unsaturated zone

    USGS Publications Warehouse

    Mills, M.S.; Michael, Thurman E.

    1994-01-01

    The preferential dealkylation pathways of the s-triazine herbicides, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine], and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], and two monodealkylated triazine metabolites, deisopropylatrazine (DIA: 2-amino-4-chloro-6-ethylamino-s-triazine) and deethylatrazine (DEA: 2-amino-4-chloro-6-isopropylamino-s-triazine) were investigated on two adjacent Eudora silt-loam plots growing corn (Zea mays L.). Results from the shallow unsaturated zone and surface-water runoff showed preferential removal of an ethyl side chain from atrazine, simazine, and DIA relative to an isopropyl side chain from atrazine, propazine, and DEA. It is hypothesized that deethylation reactions may proceed at 2-3 times the rate of deisopropylation reactions. It is concluded that small concentrations of DIA reportedly associated with the degradation of atrazine may be due to a rapid turnover rate of the metabolite in the unsaturated zone, not to small production levels. Because of continued dealkylation of both monodealkylated metabolites, a strong argument is advanced for the presence of a didealkylated metabolite in the unsaturated zone.

  13. Vertical series hydraulic conductance classes to characterize the unsaturated zone in North Carolina

    USGS Publications Warehouse

    Eimers, Jo Leslie; Terziotti, Silvia; Ferrell, Gloria M.

    2001-01-01

    This web site contains the Federal Geographic Data Committee-compliant metadata (documentation) for digital data produced for the North Carolina, Department of Environment and Natural Resources, Public Water Supply Section, Source Water Assessment Program. The metadata are for 11 individual Geographic Information System data sets. An overlay and indexing method was used with the data to derive a rating for unsaturated zone and watershed characteristics for use by the State of North Carolina in assessing more than 11,000 public water-supply wells and approximately 245 public surface-water intakes for susceptibility to contamination. For ground-water supplies, the digital data sets used in the assessment included unsaturated zone rating, vertical series hydraulic conductance, land-surface slope, and land cover. For assessment of public surface-water intakes, the data sets included watershed characteristics rating, average annual precipitation, land-surface slope, land cover, and ground-water contribution. Documentation for the land-use data set applies to both the unsaturated zone and watershed characteristics ratings. Documentation for the estimated depth-to-water map used in the calculation of the vertical series hydraulic conductance also is included.

  14. Field testing plan for unsaturated zone monitoring and field studies

    SciTech Connect

    Young, M.H.; Wierenga, P.J.; Warrick, A.W.

    1996-10-01

    The University of Arizona, in cooperation with the Bureau of Economic Geology at The University of Texas at Austin, and Stephens and Associates in Albuquerque, New Mexico has developed a field testing plan for evaluating subsurface monitoring systems. The U.S. Nuclear Regulatory Commission has requested development of these testing plans for low-level radioactive waste disposal sites (LLW) and for monitoring at decommissioned facilities designated under the {open_quotes}Site Decommissioning Management Plan{close_quotes} (SDMP). The tests are conducted on a 50 m by 50 m plot on the University of Arizona`s Maricopa Agricultural Center. Within the 50 m by 50 m plot one finds: (1) an instrumented buried trench, (2) monitoring islands similar to those proposed for the Ward Valley, California LLW Facility, (3) deep borehole monitoring sites, (4) gaseous transport monitoring, and (5) locations for testing non-invasive geophysical measurement techniques. The various subplot areas are instrumented with commercially available instruments such as neutron probes, time domain reflectometry probes, tensiometers, psychrometers, heat dissipation sensors, thermocouples, solution samplers, and cross-hole geophysics electrodes. Measurement depths vary from ground surface to 15 m. The data from the controlled flow and transport experiments, conducted over the plot, will be used to develop an integrated approach to long-term monitoring of the vadose zone at waste disposal sites. The data will also be used to test field-scale flow and transport models. This report describes in detail the design of the experiment and the methodology proposed for evaluating the data.

  15. Interfacial Soil Chemistry of Radionuclides in the Unsaturated Zone

    SciTech Connect

    Chorover, Jon; Mueller, Karl T.; Karthikeyan, K. G.; Vairavamurthy, A.; Serne, R. Jeff

    2003-06-01

    This is the final year (in a one-year extension) of a project with the principal goal of investigating the impact of clay surface alteration, resulting from hydroxy-aluminum (HyA) and hydroxyaluminosilicate (HAS) species intercalation on reactivity of soils towards Cs and Sr. Special emphasis has been accorded to the unique geochemical conditions that are representative of the Hanford site vadose zone (high ionic strength, high pH, high Al concentrations). Specific objectives of the research include: (1) Quantify the rate and extent of contaminant sorption to prevalent soil minerals as a function of system composition and contaminant concentration. (2) Determine the effects of intercalation of clays by HyA and HAS on the sorption/ion exchange process. (3) Determine the role of NOM (dissolved and mineral bound) on the particle retention of Cs and Sr. (4) Investigate the nature of mineral transformations induced by high pH and ionic strength conditions characteristic of waste impacted environments as it affects concurrent/subsequent retention of Cs and Sr. (5) Determine the coordination chemistry of contaminants bound into clay surfaces [as measured in objectives (1)-(4)] using NMR and X-ray absorption spectroscopy (XAS). Significant progress has been made in achieving these objectives. We have conducted long-term kinetic studies--reaction times ranging from 1 d to 2 yr--to examine relationships between aluminosilicate weathering in the presence of synthetic tank waste leachate (STWL) and Cs/Sr uptake and release. Our experiments employ a sequence of specimen clay minerals including illite, vermiculite, smectite and kaolinite, which are also important reactive solids in the Hanford sediments (Serne et al., 2001).

  16. Interfacial Soil Chemistry of Radionuclides in the Unsaturated Zone

    SciTech Connect

    Chorover, Jon; Mueller, Karl T.; Karthikeyan, K. G.; Vairavamurthy, A.; Serne, R. Jeff

    2002-06-01

    We are in the final year (in a one-year extension) of a project with the principal goal of investigating the impact of clay surface alteration, resulting from hydroxy-aluminum (HyA) and hydroxyaluminosilicate (HAS) species intercalation on reactivity of soils towards Cs and Sr. Special emphasis has been accorded to the unique geochemical conditions that are representative of the Hanford site vadose zone (high ionic strength, high pH, high Al concentrations). Specific objectives of the research include: (1) Quantify the rate and extent of contaminant sorption to prevalent soil minerals as a function of system composition and contaminant concentration. (2) Determine the effects of intercalation of clays by HyA and HAS on the sorption/ion exchange process. (3) Determine the role of NOM (dissolved and mineral bound) on the particle retention of Cs and Sr. (4) Investigate the nature of mineral transformations induced by high pH and ionic strength conditions characteristic of waste impacted environments as it affects concurrent/subsequent retention of Cs and Sr. (5) Determine the coordination chemistry of contaminants bound into clay surfaces [as measured in objectives (1)-(4)] using NMR and X-ray absorption spectroscopy (XAS). Significant progress has been made in achieving these objectives. We have conducted long-term kinetic studies--reaction times ranging from 1 to 370 d--to examine relationships between aluminosilicate weathering in the presence of synthetic tank waste leachate (STWL) and Cs/Sr uptake and release. Our experiments employ a sequence of specimen clay minerals including illite, vermiculite, smectite and kaolinite, which are also important reactive solids in the Hanford sediments (Serne et al., 2001). Parallel studies have been conducted with three representative Hanford sediment samples.

  17. SIMULATING RADIONUCLIDE FATE AND TRANSPORT IN THE UNSATURATED ZONE: EVALUATION AND SENSITIVITY ANALYSES OF SELECT COMPUTER MODELS

    EPA Science Inventory

    Numerical, mathematical models of water and chemical movement in soils are used as decision aids for determining soil screening levels (SSLs) of radionuclides in the unsaturated zone. Many models require extensive input parameters which include uncertainty due to soil variabil...

  18. A model for oxygen transport and consumption in the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Refsgaard, J. C.; Christensen, T. H.; Ammentorp, H. C.

    1991-12-01

    An oxygen transport and consumption model has been developed as a submodel to a general numerical model for solute transport in the unsaturated zone. The model comprises diffusive and convective transport of oxygen in soil air, convective transport and oxygen consumption in free water, and diffusive transport and a constant-rate oxygen consumption in the water-saturated soil crumbs. The model also estimates the anaerobic fraction of the water-saturated crumbs where no oxygen consumption takes place. The model dynamics and applicability are illustrated using the examples of the operation of a waste water infiltration plant and of anaerobic zones in the soil of importance for modelling denitrification.

  19. Microbial growth and transport in saturated and unsaturated porous media

    NASA Astrophysics Data System (ADS)

    Hron, Pavel; Jost, Daniel; Bastian, Peter; Ippisch, Olaf

    2014-05-01

    There is a considerable ongoing effort aimed at understanding the behavior of microorganisms in porous media. Microbial activity is of significant interest in various environmental applications such as in situ bioremediation, protection of drinking water supplies and for subsurface geochemistry in general. The main limiting factors for bacterial growth are the availability of electron acceptors, nutrients and bio-available water. The capillary fringe, defined - in a wider sense than usual - as the region of the subsurface above the groundwater table, but still dominated by capillary rise, is a region where all these factors are abundantly available. It is thus a region where high microbial activity is to be expected. In a research unit 'Dynamic Capillary Fringes - A Multidisciplinary Approach (DyCap)' founded by the German Research Foundation (DFG), the growth of microorganisms in the capillary fringe was studied experimentally and with numerical simulations. Processes like component transport and diffusion, exchange between the liquid phase and the gas phase, microbial growth and cell attachment and detachment were incorporated into a numerical simulator. The growth of the facultative anaerobic Escherichia coli as a function of nutrient availability and oxygen concentration in the liquid phase is modeled with modified Monod-type models and modifications for the switch between aerobic and anaerobic growth. Laboratory batch experiments with aqueous solutions of bacteria have been carried out under various combinations of oxygen concentrations in the gas phase and added amounts of dissolved organic carbon to determine the growth model parameters by solution of a parameter estimation problem. For the transport of bacteria the adhesion to phase boundaries is also very important. As microorganisms are transported through porous media, they are removed from the pore fluid by physicochemical filtration (attachment to sediment grain surfaces) or are adhering to gas

  20. Modeling water infiltration in unsaturated porous media by interacting lattice gas-cellular automata

    NASA Astrophysics Data System (ADS)

    di Pietro, L. B.; Melayah, A.; Zaleski, S.

    1994-10-01

    A two-dimensional lattice gas-cellular automaton fluid model with long-range interactions (Appert and Zaleski, 1990) is used to simulate saturated and unsaturated water infiltration in porous media. Water and gas within the porous medium are simulated by applying the dense and the light phase, respectively, of the cellular automaton fluid. Various wetting properties can be modeled when adjusting the corresponding solid-liquid interactions. The lattice gas rules include a gravity force step to allow buoyancy-driven flow. The model handles with ease complex geometries of the solid, and an algorithm for generating random porous media is presented. The results of four types of simulation experiments are presented: (1) We verified Poiseuille's law for steady and saturated flow between two parallel plates. (2) We analyzed transient water infiltration between two parallel plates of varying degrees of saturation and various apertures. (3) Philip's infiltration equation was adequately simulated in an unsaturated porous medium. (4) Infiltration into an aggregated medium containing one vertical parallel crack was simulated. Further applications of this lattice gas method for studying unsaturated flow in porous media are discussed.

  1. Estimation of unsaturated zone traveltimes for Rainier Mesa and Shoshone Mountain, Nevada Test Site, Nevada, using a source-responsive preferential-flow model

    SciTech Connect

    Brian A. Ebel; John R. Nimmo

    2009-09-11

    zone takes place as preferential flow, faster than would be predicted by the coupled Richards' and advection-dispersion equations with hydraulic properties estimated by traditional means. At present the hydrologic community has not achieved consensus as to whether a modification of Richards' equation, or a fundamentally different formulation, would best quantify preferential flow. Where the fastest contaminant transport speed is what needs to be estimated, there is the possibility of simplification of the evaluation process. One way of doing so is by a two-step process in which the first step is to evaluate whether significant preferential flow and solute transport is possible for the media and conditions of concern. The second step is to carry out (a) a basic Richards' and advection-dispersion equation analysis if it is concluded that preferential flow is not possible or (b) an analysis that considers only the fastest possible preferential-flow processes, if preferential flow is possible. For the preferential-flow situation, a recently published model describable as a Source-Responsive Preferential-Flow (SRPF) model is an easily applied option. This report documents the application of this two-step process to flow through the thick unsaturated zones of Rainier Mesa and Shoshone Mountain in the Nevada Test Site. Application of the SRPF model involves distinguishing between continuous and intermittent water supply to preferential flow paths. At Rainier Mesa and Shoshone Mountain this issue is complicated by the fact that contaminant travel begins at a location deep in the subsurface, where there may be perched water that may or may not act like a continuous supply, depending on such features as the connectedness of fractures and the nature of impeding layers. We have treated this situation by hypothesizing both continuous and intermittent scenarios for contaminant transport to the carbonate aquifer and reporting estimation of the fastest speed for both of these end

  2. Estimation of Unsaturated Zone Traveltimes for Rainier Mesa and Shoshone Mountain, Nevada Test Site, Nevada, Using a Source-Responsive Preferential-Flow Model

    USGS Publications Warehouse

    Ebel, Brian A.; Nimmo, John R.

    2009-01-01

    zone takes place as preferential flow, faster than would be predicted by the coupled Richards' and advection-dispersion equations with hydraulic properties estimated by traditional means. At present the hydrologic community has not achieved consensus as to whether a modification of Richards' equation, or a fundamentally different formulation, would best quantify preferential flow. Where the fastest contaminant transport speed is what needs to be estimated, there is the possibility of simplification of the evaluation process. One way of doing so is by a two-step process in which the first step is to evaluate whether significant preferential flow and solute transport is possible for the media and conditions of concern. The second step is to carry out (a) a basic Richards' and advection-dispersion equation analysis if it is concluded that preferential flow is not possible or (b) an analysis that considers only the fastest possible preferential-flow processes, if preferential flow is possible. For the preferential-flow situation, a recently published model describable as a Source-Responsive Preferential-Flow (SRPF) model is an easily applied option. This report documents the application of this two-step process to flow through the thick unsaturated zones of Rainier Mesa and Shoshone Mountain in the Nevada Test Site. Application of the SRPF model involves distinguishing between continuous and intermittent water supply to preferential flow paths. At Rainier Mesa and Shoshone Mountain this issue is complicated by the fact that contaminant travel begins at a location deep in the subsurface, where there may be perched water that may or may not act like a continuous supply, depending on such features as the connectedness of fractures and the nature of impeding layers. We have treated this situation by hypothesizing both continuous and intermittent scenarios for contaminant transport to the carbonate aquifer and reporting estimation of the fastest speed for both of th

  3. Characterization of Water and Solute Transport in the Unsaturated Zone of a Hypersaline Environment

    NASA Astrophysics Data System (ADS)

    Ronen, Daniel; Yechieli, Yoseph; Shatkay, Michal

    1996-11-01

    We present a methodology for the analysis of chemical profiles from the unsaturated zone where ions from the sediment are extracted by two methods:centrifugation and water addition. The methodology enables one to (1) assess the ion amounts present in two different phases, pore water and minerals; (2) determine the depth in the unsaturated profile where the degree of saturation of each mineral is reached; (3) establish the principal direction of water flow; and (4) differentiate between upward transport of water either as vapor or as a saline solution. The methodology was applied to the unsaturated zone of the Dead Sea coastal area where the original salinity of interstitial water in these sediments was >300 g/L. Our analysis of the field data suggests that reduction of interstitial water salinity is the result of vertical upward transport of fresh water from a confined aquifer at a depth of 7 m. Flushing, up to the potentiometric surface (depth of 3.5 m), is due to the positive pressure head of the aquifer. Above the potentiometric surface, upward water transport is due to capillary forces, and flow is maintained by evaporation at the soil surface. Evaporation leads to an increase in the salinity of the rising interstitial solution and to the sequential deposition of salts such as NaCl and KMgCl3 · 6H2O.

  4. Hydrologic inferences from strontium isotopes in pore water from the unsaturated zone at Yucca Mountain, Nevada

    SciTech Connect

    Marshall, B.D.; Futa, K.; Peterman, Z.E.

    1997-12-31

    Calcite is ubiquitous at Yucca Mountain, occurring in the soils and as fracture and cavity coatings within the volcanic tuff section. Strontium is a trace element in calcite, generally at the tens to hundreds of ppm level. Because calcite contains very little rubidium and the half-life of the {sup 87}Rb parent is billions of years, the {sup 87}Sr/{sup 86}Sr ratios of the calcite record the ratio in the water from which the calcite precipitated. Dissolution and reprecipitation does not alter these compositions so that, in the absence of other sources of strontium, one would expect the strontium ratios along a flow path to preserve variations inherited from strontium in the soil zone. Strontium isotope compositions of calcites from various settings in the Yucca Mountain region have contributed to the understanding of the unsaturated zone (UZ), especially in distinguishing unsaturated zone calcite from saturated zone calcite. Different populations of calcite have been compared, either to group them together or distinguish them from each other in terms of their strontium isotope compositions. Ground water and perched water have also been analyzed; this paper presents strontium isotope data obtained on pore water.

  5. Interpretation of chemical and isotopic data from boreholes in the unsaturated zone at Yucca Mountain, Nevada

    SciTech Connect

    Yang, I.C.; Rattray, G.W.; Yu, P.

    1996-12-31

    Analyses of pore water from boreholes at Yucca Mountain indicate that unsaturated-zone pore water has significantly larger concentrations of chloride and dissolved solids than the saturated-zone water or perched-water bodies. Chemical compositions are of the calcium sulfate or calcium chloride types in the Paintbrush Group (Tiva Canyon, Yucca Mountain, Pah Canyon, and bedded tuffs), and sodium carbonate or bicarbonate type water in the Calico Hills Formation. Tritium profiles from boreholes at Yucca Mountain indicate tritium-concentration inversions (larger tritium concentrations are located below the smaller tritium concentration in a vertical profile) occur in many places. These inversions indicate preferential flow through fractures. Rock-gas compositions are similar to that of atmospheric air except that carbon dioxide concentrations are generally larger than those in the air. The delta carbon-13 values of gas are fairly constant from surface to 365.8 meters, indicating little interaction between the gas CO{sub 2} and caliche in the soil. Model calculations indicate that the gas transport in the unsaturated zone at Yucca Mountain agrees well with the gas-diffusion process. Tritium-modeling results indicate that the high tritium value of about 100 tritium units in the Calico Hills Formation of UZ-16 is within limits of a piston-flow model with a water residence time of 32 to 35 years. The large variations in tritium concentrations with narrow peaks imply piston flow or preferential fracture flow rather than matrix flow. In reality, the aqueous-phase flow in the unsaturated zone is between piston and well-mixed flows but is closer to a piston flow.

  6. Conservation Laws for Coupled Hydro-mechanical Processes in Unsaturated Porous Media: Theory and Implementation

    SciTech Connect

    Borja, R I; White, J A

    2010-02-19

    We develop conservation laws for coupled hydro-mechanical processes in unsaturated porous media using three-phase continuum mixture theory. From the first law of thermodynamics, we identify energy-conjugate variables for constitutive modeling at macroscopic scale. Energy conjugate expressions identified relate a certain measure of effective stress to the deformation of the solid matrix, the degree of saturation to the matrix suction, the pressure in each constituent phase to the corresponding intrinsic volume change of this phase, and the seepage forces to the corresponding pressure gradients. We then develop strong and weak forms of boundary-value problems relevant for 3D finite element modeling of coupled hydro-mechanical processes in unsaturated porous media. The paper highlights a 3D numerical example illustrating the advances in the solution of large-scale coupled finite element systems, as well as the challenges in developing more predictive tools satisfying the basic conservation laws and the observed constitutive responses for unsaturated porous materials.

  7. Full-field dye concentration measurement within saturated/unsaturated thin slabs of porous media

    SciTech Connect

    Norton, D.L.; Glass, R.J.

    1992-12-31

    This paper presents a full-field dye concentration measurement technique that extends our experimental capabilities to the measurement of transient dye concentration fields within steady state flow fields under unsaturated or saturated conditions. Simple light absorption theory provides a basis for translating images into high resolution dye concentration fields. A series of dye pulse experiments that demonstrate the combined use of the full-field saturation and dye concentration techniques was conducted at four different degrees of saturation. Each of these experimental sequences was evaluated with respect to mass balance, the results being within 5% of the known dye mass input. An image windowing technique allowed us to see increased dispersion due to decreasing moisture content, tailing of concentration at the rear of the dye pulse and slight velocity changes of the dispersive front due to changes in moisture content. The exceptional resolution of dye concentration in space and time provided by this laboratory technique allows systematic experimentation for examining basic processes affecting solute transport within saturated/unsaturated porous media. Future challenges for this work will be to use these techniques to analyze more complex systems involving heterogeneities, scaling laws, and detailed investigations of the relationship between transverse and longitudinal dispersion in unsaturated media.

  8. Use of a reactive gas transport model to determine rates of hydrocarbon biodegradation in unsaturated porous media

    SciTech Connect

    Baehr, A.L.; Baker, R.J.

    1995-11-01

    A mathematical model is presented that simulates the transport and reaction of any number of gaseous phase constituents (e.g. CO{sub 2}, O{sub 2}, N{sub 2}, and hydrocarbons) in unsaturated porous media. The model was developed as part of a method to determine rates of hydrocarbon biodegradation associated with natural cleansing at petroleum product spill sites. The one-dimensional model can be applied to analyze data from column experiments or from field sites where gas transport in the unsaturated zone is approximately vertical. A coupled, non-Fickian constitutive relation between fluxes and concentration gradients, together with the capability of incorporating heterogeneity with respect to model parameters, results in model applicability over a wide range of experimental and field conditions. When applied in a calibration mode, the model allows for the determination of constituent production/consumption rates as a function of the spatial coordinate. Alternatively, the model can be applied in a predictive mode to obtain the distribution of constituent concentrations and fluxes on the the basis of assumed values of model parameters and a biodegradation hypothesis. Data requirements for the model are illustrated by analyzing data from a column experiment designed to determine the aerobic degradation rate of toluene in sediments collected from a gasoline spill site in Galloway Township, New Jersey. 15 refs., 4 figs., 4 tabs.

  9. Evolution of the conceptual model of unsaturated zone hydrology at Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Flint, Alan L.; Flint, Lorraine E.; Bodvarsson, Gudmundur S.; Kwicklis, Edward M.; Fabryka-Martin, June

    2001-06-01

    Yucca Mountain is an arid site proposed for consideration as the United States' first underground high-level radioactive waste repository. Low rainfall (approximately 170 mm/yr) and a thick unsaturated zone (500-1000 m) are important physical attributes of the site because the quantity of water likely to reach the waste and the paths and rates of movement of the water to the saturated zone under future climates would be major factors in controlling the concentrations and times of arrival of radionuclides at the surrounding accessible environment. The framework for understanding the hydrologic processes that occur at this site and that control how quickly water will penetrate through the unsaturated zone to the water table has evolved during the past 15 yr. Early conceptual models assumed that very small volumes of water infiltrated into the bedrock (0.5-4.5 mm/yr, or 2-3 percent of rainfall), that much of the infiltrated water flowed laterally within the upper nonwelded units because of capillary barrier effects, and that the remaining water flowed down faults with a small amount flowing through the matrix of the lower welded, fractured rocks. It was believed that the matrix had to be saturated for fractures to flow. However, accumulating evidence indicated that infiltration rates were higher than initially estimated, such as infiltration modeling based on neutron borehole data, bomb-pulse isotopes deep in the mountain, perched water analyses and thermal analyses. Mechanisms supporting lateral diversion did not apply at these higher fluxes, and the flux calculated in the lower welded unit exceeded the conductivity of the matrix, implying vertical flow of water in the high permeability fractures of the potential repository host rock, and disequilibrium between matrix and fracture water potentials. The development of numerical modeling methods and parameter values evolved concurrently with the conceptual model in order to account for the observed field data

  10. Predicting unsaturated zone nitrogen mass balances in agricultural settings of the United States.

    PubMed

    Nolan, Bernard T; Puckett, Larry J; Ma, Liwang; Green, Christopher T; Bayless, E Randall; Malone, Robert W

    2010-01-01

    Unsaturated zone N fate and transport were evaluated at four sites to identify the predominant pathways of N cycling: an almond [Prunus dulcis (Mill.) D.A. Webb] orchard and cornfield (Zea mays L.) in the lower Merced River study basin, California; and corn-soybean [Glycine max (L.) Merr.] rotations in study basins at Maple Creek, Nebraska, and at Morgan Creek, Maryland. We used inverse modeling with a new version of the Root Zone Water Quality Model (RZWQM2) to estimate soil hydraulic and nitrogen transformation parameters throughout the unsaturated zone; previous versions were limited to 3-m depth and relied on manual calibration. The overall goal of the modeling was to derive unsaturated zone N mass balances for the four sites. RZWQM2 showed promise for deeper simulation profiles. Relative root mean square error (RRMSE) values for predicted and observed nitrate concentrations in lysimeters were 0.40 and 0.52 for California (6.5 m depth) and Nebraska (10 m), respectively, and index of agreement (d) values were 0.60 and 0.71 (d varies between 0 and 1, with higher values indicating better agreement). For the shallow simulation profile (1 m) in Maryland, RRMSE and d for nitrate were 0.22 and 0.86, respectively. Except for Nebraska, predictions of average nitrate concentration at the bottom of the simulation profile agreed reasonably well with measured concentrations in monitoring wells. The largest additions of N were predicted to come from inorganic fertilizer (153-195 kg N ha(-1) yr(-1) in California) and N fixation (99 and 131 kg N ha(-1) yr(-1) in Maryland and Nebraska, respectively). Predicted N losses occurred primarily through plant uptake (144-237 kg N ha(-1) yr(-1)) and deep seepage out of the profile (56-102 kg N ha(-1) yr(-1)). Large reservoirs of organic N (up to 17,500 kg N ha(-1) m(-1) at Nebraska) were predicted to reside in the unsaturated zone, which has implications for potential future transfer of nitrate to groundwater. PMID:20400601

  11. Evolution of the conceptual model of unsaturated zone hydrology at yucca mountain, nevada

    SciTech Connect

    Flint, A. L.; Flint, L. E.; Bodvarsson, G. S.; Kwicklis, E. M.; Fabryka-Martin, J.

    2001-02-01

    Yucca Mountain is an arid site proposed for consideration as the United States' first underground high-level radioactive waste repository. Low rainfall (approximately 170 mm/yr) and a thick unsaturated zone (500-1000 m) are important physical attributes of the site because the quantity of water likely to reach the waste and the paths and rates of movement of the water to the saturated zone under future climates would be major factors in controlling the concentrations and times of arrival of radionuclides at the surrounding accessible environment. The framework for understanding the hydrologic processes that occur at this site and that control how quickly water will penetrate through the unsaturated zone to the water table has evolved during the past 15 yr. Early conceptual models assumed that very small volumes of water infiltrated into the bedrock (0.5-4.5 mm/yr, or 2-3 percent of rainfall), that much of the infiltrated water flowed laterally within the upper nonwelded units because o f capillary barrier effects, and that the remaining water flowed down faults with a small amount flowing through the matrix of the lower welded, fractured rocks. It was believed that the matrix had to be saturated for fractures to show. However, accumulating evidence indicated that infiltration rates were higher than initially estimated, such as infiltration modeling based on neutron borehole data, bomb-pulse isotopes deep in the mountain, perched water analyses and thermal analyses. Mechanisms supporting lateral diversion did not apply at these higher fluxes, and the flux calculated in the lower welded unit exceeded the conductivity of the matrix, implying vertical flow of water into the high permeability fractures of the potential repository host rock, and disequilibrium between matrix and fracture water potentials. The development of numerical modeling methods and parameter values evolved concurrently with the conceptual model in order to account for the observed field data

  12. Evolution of the conceptual model of unsaturated zone hydrology at Yucca Mountain, Nevada

    USGS Publications Warehouse

    Flint, Alan L.; Flint, Lorraine E.; Bodvarsson, Gudmundur S.; Kwicklis, Edward M.; Fabryka-Martin, June

    2001-01-01

    Yucca Mountain is an arid site proposed for consideration as the United States’ first underground high-level radioactive waste repository. Low rainfall (approximately 170 mm/yr) and a thick unsaturated zone (500–1000 m) are important physical attributes of the site because the quantity of water likely to reach the waste and the paths and rates of movement of the water to the saturated zone under future climates would be major factors in controlling the concentrations and times of arrival of radionuclides at the surrounding accessible environment. The framework for understanding the hydrologic processes that occur at this site and that control how quickly water will penetrate through the unsaturated zone to the water table has evolved during the past 15 yr. Early conceptual models assumed that very small volumes of water infiltrated into the bedrock (0.5–4.5 mm/yr, or 2–3 percent of rainfall), that much of the infiltrated water flowed laterally within the upper nonwelded units because of capillary barrier effects, and that the remaining water flowed down faults with a small amount flowing through the matrix of the lower welded, fractured rocks. It was believed that the matrix had to be saturated for fractures to flow. However, accumulating evidence indicated that infiltration rates were higher than initially estimated, such as infiltration modeling based on neutron borehole data, bomb-pulse isotopes deep in the mountain, perched water analyses and thermal analyses. Mechanisms supporting lateral diversion did not apply at these higher fluxes, and the flux calculated in the lower welded unit exceeded the conductivity of the matrix, implying vertical flow of water in the high permeability fractures of the potential repository host rock, and disequilibrium between matrix and fracture water potentials. The development of numerical modeling methods and parameter values evolved concurrently with the conceptual model in order to account for the observed field data

  13. Approaches to large scale unsaturated flow in heterogeneous, stratified, and fractured geologic media

    SciTech Connect

    Ababou, R.

    1991-08-01

    This report develops a broad review and assessment of quantitative modeling approaches and data requirements for large-scale subsurface flow in radioactive waste geologic repository. The data review includes discussions of controlled field experiments, existing contamination sites, and site-specific hydrogeologic conditions at Yucca Mountain. Local-scale constitutive models for the unsaturated hydrodynamic properties of geologic media are analyzed, with particular emphasis on the effect of structural characteristics of the medium. The report further reviews and analyzes large-scale hydrogeologic spatial variability from aquifer data, unsaturated soil data, and fracture network data gathered from the literature. Finally, various modeling strategies toward large-scale flow simulations are assessed, including direct high-resolution simulation, and coarse-scale simulation based on auxiliary hydrodynamic models such as single equivalent continuum and dual-porosity continuum. The roles of anisotropy, fracturing, and broad-band spatial variability are emphasized. 252 refs.

  14. Unsaturated zone hydrology and cave drip discharge water response: Implications for speleothem paleoclimate record variability

    NASA Astrophysics Data System (ADS)

    Markowska, Monika; Baker, Andy; Treble, Pauline C.; Andersen, Martin S.; Hankin, Stuart; Jex, Catherine N.; Tadros, Carol V.; Roach, Regina

    2015-10-01

    High-frequency, spatially-dense discharge monitoring was conducted over fifteen months to characterise unsaturated zone flow at Harrie Wood Cave (HWC), in the Snowy Mountains, Yarrangobilly (SE Australia). The cave was formed in the Late Silurian Yarrangobilly Limestone, a fractured rock associated with very low primary porosity due to past diagenesis. Over our monitoring period we simultaneously measured rainfall, soil moisture saturation and drip discharge rate at fourteen sites to characterise infiltration-discharge relationships. All drip discharge sites exhibited non-Gaussian distributions, indicating long periods where low discharge predominates, punctuated by short infrequent periods of high discharge. However, there was significant variability in discharge between sites and consequently no spatial correlation in the cave. We investigated the depth-discharge relationship at HWC and found a moderate relationship between depth and drip discharge lag (response) times to soil moisture content, but only weak relationships between depth and mean and maximum discharge. This highlights that the karst architecture plays an important role in controlling drip discharge dynamics. Principal Component Analysis (PCA) and Agglomerative Hierarchal Clustering (AHC) were used to classify similar drip types, revealing five unique drip regimes. Two-phase flow and non-linear response to recharge behaviour were observed, suggesting secondary porosity is controlling unsaturated zone flow in mature limestone environments with low primary porosity. Using the data presented here, the first coupled conceptual and box hydrological flow model was developed. This study highlights the heterogeneous nature of hydrological flow in karst and the need to understand unsaturated zone hydrology at the individual drip discharge level, to inform speleothem studies for high-resolution paleoclimate reconstruction.

  15. Nuclear-waste isolation in the unsaturated zone of arid regions

    SciTech Connect

    Wollenberg, H.A.; Wang, J.S.Y.; Korbin, G.

    1982-05-01

    The vadose zone in arid regions is considered as a possible environment for geologic isolation of nuclear waste. There are several topographic and lithologic combinations in the vadose zone of arid regions that may lend themselves to waste isolation considerations. In some cases, topographic highs such as mesas and interbasin ranges - comprised of several rock types, may contain essentially dry or partially saturated conditions favorable for isolation. The adjacent basins, especially in the far western and southwestern US, may have no surface or subsurface hydrologic connections with systems ultimately leading to the ocean. Some rock types may have the favorable characteristics of very low permeability and contain appropriate minerals for the strong chemical retardation of radionuclides. Environments exhibiting these hydrologic and geochemical attributes are the areas underlain by tuffaceous rocks, relatively common in the Basin and Range geomorphic province. Adjacent valley areas, where tuffaceous debris makes up a significant component of valley fill alluvium, may also contain thick zones of unsaturated material, and as such also lend themselves to strong consideration as respository environments. This paper summarizes the aspects of nuclear waste isolation in unsaturated regimes in alluvial-filled valleys and tuffaceous rocks of the Basin and Range province.

  16. Documentation of the Unsaturated-Zone Flow (UZF1) Package for modeling Unsaturated Flow Between the Land Surface and the Water Table with MODFLOW-2005

    USGS Publications Warehouse

    Niswonger, Richard G.; Prudic, David E.; Regan, R. Steven

    2006-01-01

    Percolation of precipitation through unsaturated zones is important for recharge of ground water. Rain and snowmelt at land surface are partitioned into different pathways including runoff, infiltration, evapotranspiration, unsaturated-zone storage, and recharge. A new package for MODFLOW-2005 called the Unsaturated-Zone Flow (UZF1) Package was developed to simulate water flow and storage in the unsaturated zone and to partition flow into evapotranspiration and recharge. The package also accounts for land surface runoff to streams and lakes. A kinematic wave approximation to Richards? equation is solved by the method of characteristics to simulate vertical unsaturated flow. The approach assumes that unsaturated flow occurs in response to gravity potential gradients only and ignores negative potential gradients; the approach further assumes uniform hydraulic properties in the unsaturated zone for each vertical column of model cells. The Brooks-Corey function is used to define the relation between unsaturated hydraulic conductivity and water content. Variables used by the UZF1 Package include initial and saturated water contents, saturated vertical hydraulic conductivity, and an exponent in the Brooks-Corey function. Residual water content is calculated internally by the UZF1 Package on the basis of the difference between saturated water content and specific yield. The UZF1 Package is a substitution for the Recharge and Evapotranspiration Packages of MODFLOW-2005. The UZF1 Package differs from the Recharge Package in that an infiltration rate is applied at land surface instead of a specified recharge rate directly to ground water. The applied infiltration rate is further limited by the saturated vertical hydraulic conductivity. The UZF1 Package differs from the Evapotranspiration Package in that evapotranspiration losses are first removed from the unsaturated zone above the evapotranspiration extinction depth, and if the demand is not met, water can be removed

  17. Hydrologic characterization of faults and other potentially conductive geologic features in the unsaturated zone

    SciTech Connect

    Javandel, I.; Shan, C.

    1990-01-01

    The capability of characterizing near-vertical faults and other potentially highly conductive geologic features in the vicinity of a high-level-waste repository is of great importance in site characterization of underground waste-isolation projects. The possibility of using transient air pressure data at depth for characterizing these features in the unsaturated zone are investigated. Analytical solutions for calculating the pressure response of such systems are presented. Solutions are given for two types of barometric pressure fluctuations, step function and sinusoidal. 3 refs., 9 figs.

  18. Assessing aquifer contamination risk using immunoassay: trace analysis of atrazine in unsaturated zone sediments

    USGS Publications Warehouse

    Juracek, K.E.; Thurman, E.M.

    1997-01-01

    The vulnerability of a shallow aquifer in south-central Kansas to contamination by atrazine (2-chloro-4-ethylamino-6-isopropylamines-triazine) was assessed by analyzing unsaturated zone soil and sediment samples from about 60 dryland and irrigated sites using an ultrasensitive immunoassay (detection level of 0.02 µg/kg) with verification by gas chromatography/mass spectrometry (GC/MS). Samples were collected at depths of 0 to 1.2 m (i.e., the root zone), 1.2 to 1.8 m, and 1.8 to 3.0 m during two time periods-prior to planting and after harvest of crops. About 75% of the samples contained detectable concentrations of parent atrazine. At the shallow sampling depth, atrazine concentrations ranged from 0.5 to approximately 12 µg/kg. Atrazine concentrations at the intermediate (1.2-1.8 m) depth generally were <1.0 µg/kg, with most of the concentrations <0.10 µg/kg, which suggests substantial degradation of parent atrazine in the root zone. Likewise, atrazine concentrations front the deepest (1.8-3.0 m) depth ranged from <0.02 to 0.33 µg/kg. The metabolite deethylatrazine (2-amino-4-chloro-6- isopropylamine-s-triazine) was detected by GC/MS only in 2 of 60 samples with concentrations of 1.4 and 1.5 µg/kg. The reconnaissance survey shows that, in spite of atrazine use ranging from 1 to 5 or more years, there does not appear to he a significant buildup of parent compound below the root zone. Therefore, the unsaturated zone does not appear to be a major storage compartment of atrazine contamination for the underlying shallow aquifer.

  19. Investigation of Episodic Flow from Unsaturated Porous Media into a Macropore

    SciTech Connect

    R. K. Podgorney; J. P. Fairley

    2008-02-01

    Th e recent literature contains numerous observations of episodic or intermittent fl ow in unsaturated flow systems under both constant fl ux and ponded boundary conditions. Flow systems composed of a heterogeneous porous media, as well as discrete fracture networks, have been cited as examples of systems that can exhibit episodic fl ow. Episodic outfl ow events are significant because relatively large volumes of water can move rapidly through an unsaturated system, carrying water and contaminants to depth greatly ahead of a wetting front predicted by a one-dimensional, gravity-driven diff usive infiltration model. In this study, we model the behavior of water flow through a sand column underlain by an impermeable-walled macropore. Relative permeability and capillary pressure relationships were developed that capture the complex interrelationships between the macropore and the overlying porous media that control fl ow out of the system. The potential for episodic flow is assessed and compared to results of conventional modeling approaches and experimental data from the literature. Model results using coupled matrix–macropore relative permeability and capillary pressure relationships capture the behavior observed in laboratory experiments remarkably well, while simulations using conventional relative permeability and capillary pressure functions fail to capture some of the observed fl ow dynamics. Capturing the rapid downward movement of water suggests that the matrix-macropore capillary pressure and relative permeability functions developed have the potential to improve descriptions of fl ow and transport processes in heterogeneous, variably saturated media.

  20. Transport and retention of fullerene (nC60) nanoparticles in unsaturated porous media: effects of solution chemistry and solid phase coating.

    PubMed

    Chen, Lixia; Sabatini, David A; Kibbey, Tohren C G

    2012-09-01

    The retention and release of aqueous aggregates of fullerene nanoparticles (nC(60)) were studied under dynamic unsaturated conditions. Porous media containing nC(60) were taken through multiple drainage/imbibition (drying/wetting) cycles to explore the effects of solution conditions and solid surface modification on transport and ultimate fate in unsaturated porous media. In experiments conducted with NaCl as the background electrolyte, the retention of nC(60) during drainage was found to be negligibly small over a wide range of ionic strengths (I=0.2 to I=6 mM), significantly lower than the retention of titanium dioxide nanoparticles studied previously under similar conditions. In contrast, experiments conducted with CaCl(2) as the background electrolyte found that retention of nC(60) during drainage was significant at higher ionic strengths, particularly at the highest ionic strength studied (I=6 mM). Experiments examining the influence of dissolved natural organic matter on nC(60) retention in unsaturated media found no measurable impact on the transport. The effects of solid surface modification were examined by creating coatings that modified surface hydrophobicity and charge. Experiments found that a hydrophobic coating had no measurable impact on nC(60) retention, when compared with retention by unmodified media. In contrast, a porous medium with surfaces that were both hydrophobic and positively-charged retained 5-10 times more nC(60) during drainage than an unmodified porous medium. This result suggests that electrostatic interactions play a more important role than hydrophobic interactions in the transport and fate of nC(60) in the unsaturated zone. For all conditions where retention was observed, experiments found very little release or retained nC(60) after subsequent flushing with water, suggesting that once retained, the environmental mobility of nC(60) may be extremely limited. PMID:22858671

  1. Coupled Hydromechanical and Electromagnetic Responses in Unsaturated Porous Media: Theory, Observation, and Numerical Simulations

    NASA Astrophysics Data System (ADS)

    Mahardika, Harry

    Hydromechanical energy can be partially converted into electromagnetic energy due to electrokinetic effect, where mechanical energy causes the relative displacement of the charged pore water with respect to the solid skeleton of the porous material and generated electrical current density. An application of this phenomenon is seismoelectric method, a geophysical method in which electromagnetic signals are recorded and associated with the propagation of seismic waves. Due to its coupling nature, seismoelectric method promises advantages in characterizing the subsurface properties and geometry compared to independent employments of seismic or electromagnetic acquisition alone. Since the recorded seismoelectric signal are sensitive to water content changes this method have been applied for groundwater studies to delineates vadoze zone-aquifer boundary since the last twenty years. The problem, however, the existing governing equations of coupled seismic and electromagnetic are not accounted for unsaturated conditions and its petrophysical sensitivity to water content. In this thesis we extend the applications of seismoelectric method for unsaturated porous medium for several geophysical problems. (1) We begin our study with numerical study to localize and characterize a seismic event induced by hydraulic fracturing operation sedimentary rocks. In this problem, we use the fully-saturated case of seismoelectric method and we propose a new joint inversion scheme (seismic and seismoelectric) to determine the position and moment tensor that event. (2) We expand the seismoelectric theory for unsaturated condition and show that the generation of electrical current density are depend on several important petrophysical properties that are sensitive to water content. This new expansion of governing equation provide us theory for developing a new approach for seismoelectric method to image the oil water encroachment front during water flooding of an oil reservoir or an aquifer

  2. Transport of solutes through unsaturated fractured media: Nevada Nuclear Waste Storage Investigations Project

    SciTech Connect

    Dykhuizen, R.C.

    1988-03-01

    A numerical model is presented to represent the transport of solutes through a highly fractured unsaturated, porous medium. To accomplish this, the solute is tracked separately in two flow systems a matrix pore flow system and a fracture network, with interaction terms. Compatible hydraulic equations for such a dual system are also presented to enable solution of the solute trasport. The hydraulic equations chosen use the equivlaent porous media concept. These equations can also be applied to a saturated medium without modification. However, many of the transport terms will be negligible for such an application. A brief sample calculation illustates the method. 11 refs., 4 figs.

  3. Does Water Content or Flow Rate Control Colloid Transport in Unsaturated Porous Media?

    SciTech Connect

    Thorsten Knappenberger; Markus Flury; Earl D. Mattson; James B. Harsh

    2014-03-01

    Mobile colloids can play an important role in contaminant transport in soils: many contaminants exist in colloidal form, and colloids can facilitate transport of otherwise immobile contaminants. In unsaturated soils, colloid transport is, among other factors, affected by water content and flow rate. Our objective was to determine whether water content or flow rate is more important for colloid transport. We passed negatively charged polystyrene colloids (220 nm diameter) through unsaturated sand-filled columns under steady-state flow at different water contents (effective water saturations Se ranging from 0.1 to 1.0, with Se = (? – ?r)/(?s – ?r)) and flow rates (pore water velocities v of 5 and 10 cm/min). Water content was the dominant factor in our experiments. Colloid transport decreased with decreasing water content, and below a critical water content (Se < 0.1), colloid transport was inhibited, and colloids were strained in water films. Pendular ring and water film thickness calculations indicated that colloids can move only when pendular rings are interconnected. The flow rate affected retention of colloids in the secondary energy minimum, with less colloids being trapped when the flow rate increased. These results confirm the importance of both water content and flow rate for colloid transport in unsaturated porous media and highlight the dominant role of water content.

  4. Comparison of strongly heat-driven flow codes for unsaturated media

    SciTech Connect

    Updegraff, C.D.

    1989-08-01

    Under the sponsorship of the US Nuclear Regulatory Commission, Sandia National Laboratories (SNL) is developing a performance assessment methodology for the analysis of long-term disposal of high-level radioactive waste (HLW) in unsaturated welded tuff. As part of this effort, SNL evaluated existing strongly heat-driven flow computer codes for simulating ground-water flow in unsaturated media. The three codes tested, NORIA, PETROS, and TOUGH, were compared against a suite of problems for which analytical and numerical solutions or experimental results exist. The problems were selected to test the abilities of the codes to simulate situations ranging from simple, uncoupled processes, such as two-phase flow or heat transfer, to fully coupled processes, such as vaporization caused by high temperatures. In general, all three codes were found to be difficult to use because of (1) built-in time stepping criteria, (2) the treatment of boundary conditions, and (3) handling of evaporation/condensation problems. A drawback of the study was that adequate problems related to expected repository conditions were not available in the literature. Nevertheless, the results of this study suggest the need for thorough investigations of the impact of heat on the flow field in the vicinity of an unsaturated HLW repository. Recommendations are to develop a new flow code combining the best features of these three codes and eliminating the worst ones. 19 refs., 49 figs.

  5. Conceptual hydrologic model of flow in the unsaturated zone, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Montazer, P.M.; Wilson, W.E.

    1984-01-01

    The unsaturated volcanic tuffs beneath Yucca Mountain, Nevada, are being evaluated as a host rock for a potential repository for high-level radioactive waste. A conceptual hydrologic model is proposed to describe the flow of fluids through these rocks. Thickness of the unsaturated zone is about 500 to 750 meters and consists of three welded units interlayered with two nonwelded units. Compared to nonwelded units, welded units have low matrix porosities and permeabilities, high fracture densities, and high bulk hydraulic conductivities. The principal repository area is bounded by normal fault zones. Of the average annual precipitation of 150 millimeters per year, 0.5 to 4.5 millimeters per year becomes net infiltration. Percolation through the matrix of the welded units is principally vertical and is less than 1 millimeter per year. Percolation through nonwelded units occurs both vertically and laterally and has variable rates (0.1 to 100 millimeters per year). Fracture flow is predominant in the uppermost welded unit during intense pulses of infiltration, but is insignificant in the welded unit that forms the potential host rock. Lateral flow in the upper nonwelded unit, enhanced by existence of a capillary barrier, probably is the factor controlling the low fluxes in the host rock and relatively high fluxes in the structural features. (USGS)

  6. Isotopic data of pore water extracted from unsaturated-zone cores at Yucca Mountain, Nevada

    SciTech Connect

    Yang, I.C.

    1997-12-01

    Isotopic compositions of unsaturated-zone (UZ) ground water ({delta}{sup 18}O, {delta}D, {delta}{sup 13}C and {sup 14}C) at Yucca Mountain, Nevada, the site of a potential permanent national nuclear waste repository, can be used to infer the origins of water, residence times of the water, water flux, climatic and evaporative history of water, flow paths and velocities. These data can also be used as indicators of transport properties or water-rock interaction. The lack of long-term direct measurements of infiltration requires proxy indicators of water movement through the unsaturated zone to extend the record into the past. This report will discuss {delta}D and {delta}{sup 18}O data obtained from pore water, along with the {delta}{sup 13}C and {sup 14}C data of gas and water obtained from four boreholes dry-drilled through all UZ lithologic units to infer the existence of nonvertical flowpaths through the mountain and residence times of pore water.

  7. SESOIL. Code System Calculate One-Dimensional Vertical Transport Unsaturated Soil Zone

    SciTech Connect

    Scott, S.J.; Hetrick, D.M.

    1994-08-01

    SESOIL, as an integrated screening-level soil compartment model, is designed to simultaneously model water transport, sediment transport, and pollutant fate. SESOIL is a one-dimensional vertical transport model for the unsaturated soil zone. Only one compound at a time can be considered. The model is based on mass balance and equilibrium partitioning of the chemical between different phases (dissolved, sorbed, vapor, and pure). The SESOIL model was designed to perform long-term simulations of chemical transport and transformations in the soil and uses theoretically derived equations to represent water transport, sediment transport on the land surface, pollutant transformation, and migration of the pollutant to the atmosphere and groundwater. Climatic data, compartment geometry, and soil and chemical property data are the major components used in the equations. SESOIL was developed as a screening-level model, utilizing less soil, chemical, and meteorological values as input than most other similar models. Output of SESOIL includes time-varying pollutant concentrations at various soil depths and pollutant loss from the unsaturated zone in terms of surface runoff, percolation to the groundwater, volatilization, and degradation. The February 1995 release corrects an error that caused the code to fail when average monthly air temperature was -10C and includes an improved iteration procedure for the mass balance equations in the model.

  8. A borehole instrumentation program for characterization of unsaturated-zone percolation

    SciTech Connect

    Kume, J.; Rousseau, J.P.

    1994-12-31

    A borehole instrumentation and monitoring program has been designed by the US Geological Survey to support site characterization of unsaturated-zone percolation at Yucca Mountain, Nye County, Nevada. This program provides a means of defining the unsaturated-zone fluid flow (liquid and gas) potential field in a setting that incorporates large-scale stratigraphic and structural features, and the influences of geothermal heat flow and atmospheric pressure changes. Data derived from this program will be used to evaluate the suitability of Yucca Mountain as a mined geologic-repository for the storage of high-level, radioactive waste. These data include in-situ temperature, pneumatic pressure, and water potential. In addition, the instrumentation program provides facilities for gas-sampling, gas-tracer diffusion testing, water-injection testing, water-level monitoring, neutron moisture-meter monitoring, temperature profiling, and in-situ recalibration of the downhole sensors. The program included testing and development of: (1) precision sensors for measurement; (2) a downhole instrumentation-station-apparatus to house the sensors, recalibrate sensors in-situ, and allow access to instrument stations for other testing purposes; and (3) surface-based support and instrumentation facilities.

  9. Estimation of rates of aerobic hydrocarbon biodegradation by simulation of gas transport in the unsaturated zone

    USGS Publications Warehouse

    Lahvis, M.A.; Baehr, A.L.

    1996-01-01

    The distribution of oxygen and carbon dioxide gases in the unsaturated zone provides a geochemical signature of aerobic hydrocarbon degradation at petroleum product spill sites. The fluxes of these gases are proportional to the rate of aerobic biodegradation and are quantified by calibrating a mathematical transport model to the oxygen and carbon dioxide gas concentration data. Reaction stoichiometry is assumed to convert the gas fluxes to a corresponding rate of hydrocarbon degradation. The method is applied at a gasoline spill site in Galloway Township, New Jersey, to determine the rate of aerobic degradation of hydrocarbons associated with passive and bioventing remediation field experiments. At the site, microbial degradation of hydrocarbons near the water table limits the migration of hydrocarbon solutes in groundwater and prevents hydrocarbon volatilization into the unsaturated zone. In the passive remediation experiment a site-wide degradation rate estimate of 34,400 g yr-1 (11.7 gal. yr-1) of hydrocarbon was obtained by model calibration to carbon dioxide gas concentration data collected in December 1989. In the bioventing experiment, degradation rate estimates of 46.0 and 47.9 g m-2 yr-1 (1.45 x 10-3 and 1.51 x 10-3 gal. ft.-2 yr-1) of hydrocarbon were obtained by model calibration to oxygen and carbon dioxide gas concentration data, respectively. Method application was successful in quantifying the significance of a naturally occurring process that can effectively contribute to plume stabilization.

  10. Field determination of vertical permeability to air in the unsaturated zone

    USGS Publications Warehouse

    Weeks, Edwin P.

    1978-01-01

    The vertical permeability to air of layered materials in the unsaturated zone may be determined from air pressure data obtained at depth during a period when air pressure is changing at land surface. Such data may be obtained by monitoring barometric pressure with a microbarograph or surveying altimeter and simultaneously measuring down-hole pneumatic head differences in specially constructed piezometers. These data, coupled with air-filled porosity data from other sources, may be compared with the results of electric-analog or numerical solution of the one-dimensional diffusion equation to make a trial-and-error determination of the air permeability for each layer. The permeabilities to air may in turn be converted to equivalent hydraulic conductivity values if the materials are well drained, are permeable enough that the Klinkenberg effect is small, and are structurally unaffected by wetting. The method offers potential advantages over present methods to evaluate sites for artificial recharge by spreading; to evaluate ground-water pollution hazards from feedlots, sanitary landfills , and land irrigated with sewage effluent; and to evaluate sites for temporary storage of gas in the unsaturated zone. (Woodard-USGS)

  11. Flow-path textures and mineralogy in tuffs of the unsaturated zone

    USGS Publications Warehouse

    Levy, Schön; Chipera, Steve; WoldeGabriel, Giday; Fabryka-Martin, June; Roach, Jeffrey; Sweetkind, Donald S.

    1999-01-01

    The high concentration of chlorine-36 (36Cl) produced by above-ground nuclear tests (bomb-pulse) provides a fortuitous tracer for infiltration during the last 50 years, and is used to detect fast flow in the unsaturated zone at Yucca Mountain, Nevada, a thick deposit of welded and nonwelded tuffs. Evidence of fast flow as much as 300 m into the mountain has been found in several zones in a 7.7-km tunnel. Many zones are associated with faults that provide continuous fracture flow paths from the surface. In the Sundance fault zone, water with the bomb-pulse signature has moved into subsidiary fractures and breccia zones. We found no highly distinctive mineralogic associations of fault and fracture samples containing bomb-pulse 36Cl. Bomb-pulse sites are slightly more likely to have calcite deposits than are non-bomb-pulse sites. Most other mineralogic and textural associations of fast-flow paths reflect the structural processes leading to locally enhanced permeability rather than the effects of ground-water percolation. Water movement through the rock was investigated by isotopic analysis of paired samples representing breccia zones and fractured wall rock bounding the breccia zones. Where bomb-pulse 36Cl is present, the waters in bounding fractures and intergranular pores of the fast pathways are not in equilibrium with respect to the isotopic signal. In structural domains that have experienced extensional deformation, fluid flow within a breccia is equivalent to matrix flow in a particulate rock, whereas true fracture flow occurs along the boundaries of a breccia zone. Where shearing predominated over extension, the boundary between wall rock and breccia is rough and irregular with a tight wallrock/breccia contact. The absence of a gap between the breccia and the wall rock helps maintain fluid flow within the breccia instead of along the wallrock/breccia boundary, leading to higher 36Cl/Cl values in the breccia than in the wall rock.

  12. Plant Production Systems for Microgravity: Critical Issues in Water, Air, and Solute Transport Through Unsaturated Porous Media

    NASA Technical Reports Server (NTRS)

    Steinberg, Susan L. (Editor); Ming, Doug W. (Editor); Henninger, Don (Editor)

    2002-01-01

    This NASA Technical Memorandum is a compilation of presentations and discussions in the form of minutes from a workshop entitled 'Plant Production Systems for Microgravity: Critical Issues in Water, Air, and Solute Transport Through Unsaturated Porous Media' held at NASA's Johnson Space Center, July 24-25, 2000. This workshop arose from the growing belief within NASA's Advanced Life Support Program that further advances and improvements in plant production systems for microgravity would benefit from additional knowledge of fundamental processes occurring in the root zone. The objective of the workshop was to bring together individuals who had expertise in various areas of fluid physics, soil physics, plant physiology, hardware development, and flight tests to identify, discuss, and prioritize critical issues of water and air flow through porous media in microgravity. Participants of the workshop included representatives from private companies involved in flight hardware development and scientists from universities and NASA Centers with expertise in plant flight tests, plant physiology, fluid physics, and soil physics.

  13. Novel methods for measuring air-water interfacial area in unsaturated porous media.

    PubMed

    Brusseau, Mark L; El Ouni, Asma; Araujo, Juliana B; Zhong, Hua

    2015-05-01

    Interfacial partitioning tracer tests (IPTT) are used to measure air-water interfacial area for unsaturated porous media. The standard IPTT method involves conducting tests wherein an aqueous surfactant solution is introduced into a packed column under unsaturated flow conditions. Surfactant-induced drainage has been observed to occur for this method in some cases, which can complicate data analysis and impart uncertainty to the measured values. Two novel alternative approaches for conducting IPTTs are presented herein that are designed in part to prevent surfactant-induced drainage. The two methods are termed the dual-surfactant IPTT (IPTT-DS) and the residual-air IPTT (IPTT-RA). The two methods were used to measure air-water interfacial areas for two natural porous media. System monitoring during the tests revealed no measurable surfactant-induced drainage. The measured interfacial areas compared well to those obtained with the standard IPTT method conducted in such a manner that surfactant-induced drainage was prevented. PMID:25732632

  14. NOVEL METHODS FOR MEASURING AIR-WATER INTERFACIAL AREA IN UNSATURATED POROUS MEDIA

    PubMed Central

    Brusseau, Mark L.; Ouni, Asma El; Araujo, Juliana B.; Zhong, Hua

    2015-01-01

    Interfacial partitioning tracer tests (IPTT) are used to measure air-water interfacial area for unsaturated porous media. The standard IPTT method involves conducting tests wherein an aqueous surfactant solution is introduced into a packed column under unsaturated flow conditions. Surfactant-induced drainage has been observed to occur for this method in some cases, which can complicate data analysis and impart uncertainty to the measured values. Two novel alternative approaches for conducting IPTTs are presented herein that are designed in part to prevent surfactant-induced drainage. The two methods are termed the dual-surfactant IPTT (IPTT-DS) and the residual-air IPTT (IPTT-RA). The two methods were used to measure air-water interfacial areas for two natural porous media. System monitoring during the tests revealed no measurable surfactant-induced drainage. The measured interfacial areas compared well to those obtained with the standard IPTT method conducted in such a manner that surfactant-induced drainage was prevented. PMID:25732632

  15. Analytical and numerical analyses of an unconfined aquifer test considering unsaturated zone characteristics

    NASA Astrophysics Data System (ADS)

    Moench, Allen F.

    2008-06-01

    A 7-d, constant rate aquifer test conducted by University of Waterloo researchers at Canadian Forces Base Borden in Ontario, Canada, is useful for advancing understanding of fluid flow processes in response to pumping from an unconfined aquifer. Measured data include not only drawdown in the saturated zone but also volumetric soil moisture measured at various times and distances from the pumped well. Analytical analyses were conducted with the model published in 2001 by Moench and colleagues, which allows for gradual drainage but does not include unsaturated zone characteristics, and the model published in 2006 by Mathias and Butler, which assumes that moisture retention and relative hydraulic conductivity (RHC) in the unsaturated zone are exponential functions of pressure head. Parameters estimated with either model yield good matches between measured and simulated drawdowns in piezometers. Numerical analyses were conducted with two versions of VS2DT: one that uses traditional Brooks and Corey functional relations and one that uses a RHC function introduced in 2001 by Assouline that includes an additional parameter that accounts for soil structure and texture. The analytical model of Mathias and Butler and numerical model of VS2DT with the Assouline model both show that the RHC function must contain a fitting parameter that is different from that used in the moisture retention function. Results show the influence of field-scale heterogeneity and suggest that the RHC at the Borden site declines more rapidly with elevation above the top of the capillary fringe than would be expected if the parameters were to reflect local- or core-scale soil structure and texture.

  16. Analytical and numerical analyses of an unconfined aquifer test considering unsaturated zone characteristics

    USGS Publications Warehouse

    Moench, A.F.

    2008-01-01

    A 7-d, constant rate aquifer test conducted by University of Waterloo researchers at Canadian Forces Base Borden in Ontario, Canada, is useful for advancing understanding of fluid flow processes in response to pumping from an unconfined aquifer. Measured data include not only drawdown in the saturated zone but also volumetric soil moisture measured at various times and distances from the pumped well. Analytical analyses were conducted with the model published in 2001 by Moench and colleagues, which allows for gradual drainage but does not include unsaturated zone characteristics, and the model published in 2006 by Mathias and Butler, which assumes that moisture retention and relative hydraulic conductivity (RHC) in the unsaturated zone are exponential functions of pressure head. Parameters estimated with either model yield good matches between measured and simulated drawdowns in piezometers. Numerical analyses were conducted with two versions of VS2DT: one that uses traditional Brooks and Corey functional relations and one that uses a RHC function introduced in 2001 by Assouline that includes an additional parameter that accounts for soil structure and texture. The analytical model of Mathias and Butler and numerical model of VS2DT with the Assouline model both show that the RHC function must contain a fitting parameter that is different from that used in the moisture retention function. Results show the influence of field-scale heterogeneity and suggest that the RHC at the Borden site declines more rapidly with elevation above the top of the capillary fringe than would be expected if the parameters were to reflect local- or core-scale soil structure and texture.

  17. Biodegradation of vapor-phase toluene in unsaturated porous media: Column experiments.

    PubMed

    Khan, Ali M; Wick, Lukas Y; Harms, Hauke; Thullner, Martin

    2016-04-01

    Biodegradation of organic chemicals in the vapor phase of soils and vertical flow filters has gained attention as promising approach to clean up volatile organic compounds (VOC). The drivers of VOC biodegradation in unsaturated systems however still remain poorly understood. Here, we analyzed the processes controlling aerobic VOC biodegradation in a laboratory setup mimicking the unsaturated zone above a shallow aquifer. The setup allowed for diffusive vapor-phase transport and biodegradation of three VOC: non-deuterated and deuterated toluene as two compounds of highly differing biodegradability but (nearly) identical physical and chemical properties, and MTBE as (at the applied experimental conditions) non-biodegradable tracer and internal control. Our results showed for toluene an effective microbial degradation within centimeter VOC transport distances despite high gas-phase diffusivity. Degradation rates were controlled by the reactivity of the compounds while oxic conditions were found everywhere in the system. This confirms hypotheses that vadose zone biodegradation rates can be extremely high and are able to prevent the outgassing of VOC to the atmosphere within a centimeter range if compound properties and site conditions allow for sufficiently high degradation rates. PMID:26774779

  18. Comparison of three techniques to measure unsaturated-zone air permeability at Picatinny Arsenal, NJ

    NASA Astrophysics Data System (ADS)

    Olson, Mira Stone; Tillman, Fred D.; Choi, Jee-Won; Smith, James A.

    2001-12-01

    The purpose of this study is to compare three techniques to measure the air permeability of the unsaturated zone at Picatinny Arsenal, NJ and to examine the effects of moisture content and soil heterogeneity on air permeability. Air permeability was measured in three ways: laboratory experiments on intact soil cores, field-scale air pump tests and calibration of air permeability to air pressures measured in the field under natural air pressure conditions using a numerical airflow model. The results obtained from these three methods were compared and found to be similar. Laboratory experiments performed on intact cores measured air permeability values on the order of 10 -14 to 10 -9 m 2. Low-permeability cores were found between land surface and a depth of 0.6 m. The soil core data were divided into two layers with composite vertical permeability values of 1.3×10 -13 m 2 from land surface to a 0.6-m depth and 3.8×10 -10 m 2 for the lower layer. Analyses of the field-scale pump tests were performed for two scenarios: one in which the entire unsaturated zone was open to the atmosphere and one assuming a cap of low permeability extending 0.6 m below land surface. The vertical air permeability values obtained for the open scenario ranged from 1.2×10 -9 to 1.5×10 -9 m 2, and ranged from 3.6×10 -9 to 6.8×10 -9 m 2 in the lower layer, assuming an upper cap permeability of 6.0×10 -14 m 2. The results from the open scenario are much higher than expected and the possible reasons for this ambiguity are discussed. The results from the capped scenario matched closely with those from the other methods and indicated that it is important to have background information on the study site to correctly analyze the pump test data. The optimized fit of the natural subsurface air pressure was achieved with an intrinsic permeability value of 3.3×10 -14 m 2. When the data were refitted to the model assuming two distinct layers of the unsaturated zone, the optimized fit was achieved

  19. Nitrate behaviors in unsaturated zone under farmlands with different fertilization log at Kumamoto region, Japan.

    NASA Astrophysics Data System (ADS)

    Okumura, Azusa; Hosono, Takahiro; Shimada, Jun

    2016-04-01

    Excessive application of fertilizer and manure in agricultural activities often caused an increase of nitrate concentration in groundwater. The study area, Kumamoto is also facing this type of problem. Previous studies using nitrogen-oxygen isotope ratios in nitrate, it was shown that accumulation of chemical fertilizer is the major factor of nitrate contamination in the Kumamoto region. However, once it loaded nitrogen component may change its form and isotopic composition during downwards transportation into the aquifer. Especially, in the study area where the groundwater is recharged through a thick unsaturated zone, and therefore, it is important to elucidate the phenomenon happened in the soil zone of this area. However, it has not been. To clarify the behavior of nitrogen and the change of nitrate concentration in the unsaturated zone, we analyzed the nitrogen-oxygen isotope ratios of the extracted soil water of the unsaturated zone soils, sampled in the farmland having different fertilization logs. In addition, we attempted to verify the origin of groundwater contamination by comparing with previous results. The plateaus-like topography of the study area is consists of the pyroclastic flow deposits. Land use is mainly farmland and this area is a major source of nitrogen load and transport route into the aquifer. Nitrate concentration in groundwater at terraces recharge area has been reported about 40 mg/L. Drilling survey carried out in the unsaturated zone soil on 4 farmlands with the different land use logs in such terraces. Drilling point KO and KTO were treated by both slurry and chemical fertilizers, on the other hand, point M1 and M2 were fertilized by only chemical fertilizers. The drilling depth was up to 14-15 m, and soil samples were kept on evacuated condition after sectioning into 10 cm interval. The soil water was extracted using a centrifuge machine. The extracted soil water was measured for the nitrogen-oxygen isotope ratios in nitrate and

  20. Parallel computing simulation of fluid flow in the unsaturated zone of Yucca Mountain, Nevada.

    PubMed

    Zhang, Keni; Wu, Yu-Shu; Bodvarsson, G S

    2003-01-01

    This paper presents the application of parallel computing techniques to large-scale modeling of fluid flow in the unsaturated zone (UZ) at Yucca Mountain, Nevada. In this study, parallel computing techniques, as implemented into the TOUGH2 code, are applied in large-scale numerical simulations on a distributed-memory parallel computer. The modeling study has been conducted using an over-1-million-cell three-dimensional numerical model, which incorporates a wide variety of field data for the highly heterogeneous fractured formation at Yucca Mountain. The objective of this study is to analyze the impact of various surface infiltration scenarios (under current and possible future climates) on flow through the UZ system, using various hydrogeological conceptual models with refined grids. The results indicate that the 1-million-cell models produce better resolution results and reveal some flow patterns that cannot be obtained using coarse-grid modeling models. PMID:12714301

  1. Simulating the Thermal History of the Unsaturated Zone at Yucca Mountain, Nevada

    SciTech Connect

    B.D. Marshal; J.F. Whelan

    2001-07-23

    Heat transfer within Earth's upper crust is primarily by conduction, and conductive thermal models adequately explain the cooling history of deep, batholith-scale intrusions and surrounding wall rocks, as confirmed by numerous thermochronometric studies. However, caldera magmatic systems require consideration of the small and localized component of hydrothermal convection and numerical models to simulate additional boundary conditions, irregular magma chamber shapes, and complex intrusive histories. At Yucca Mountain, Nevada, the site of a potential high-level nuclear waste repository, simulating the detailed thermal history at any location in the unsaturated zone requires knowledge of the shape of the magma chamber and its proximity to Yucca Mountain (the southern margin of the Timber Mountain caldera complex is approximately 8 km north of the potential repository site), the temporal and spatial extent of hydrothermal convection, the erosional history of the area, and past levels of the water table.

  2. Massively parallel computing simulation of fluid flow in the unsaturated zone of Yucca Mountain, Nevada

    SciTech Connect

    Zhang, Keni; Wu, Yu-Shu; Bodvarsson, G.S.

    2001-08-31

    This paper presents the application of parallel computing techniques to large-scale modeling of fluid flow in the unsaturated zone (UZ) at Yucca Mountain, Nevada. In this study, parallel computing techniques, as implemented into the TOUGH2 code, are applied in large-scale numerical simulations on a distributed-memory parallel computer. The modeling study has been conducted using an over-one-million-cell three-dimensional numerical model, which incorporates a wide variety of field data for the highly heterogeneous fractured formation at Yucca Mountain. The objective of this study is to analyze the impact of various surface infiltration scenarios (under current and possible future climates) on flow through the UZ system, using various hydrogeological conceptual models with refined grids. The results indicate that the one-million-cell models produce better resolution results and reveal some flow patterns that cannot be obtained using coarse-grid modeling models.

  3. Observations on preferential flow and horizontal transport of nitrogen fertilizer in the unsaturated zone

    USGS Publications Warehouse

    Wilkison, D.H.; Blevins, D.W.

    1999-01-01

    A study site underlain by a claypan soil was instrumented to examine the transport of fertilizer nitrogen (N) under corn (Zea mays L.) cultivation. The study was designed to examine N transport within the unsaturated zone and in interflow (the saturated flow of water on top of the claypan). A 15N- labeled fertilizer (labeled N), bromide (Br), and chloride (Cl) were used as field tracers. Rapid or prolonged infiltration events allowed water and dissolved solutes to perch on the claypan for brief periods. However, a well- developed network of preferential flow paths quickly diverted water and solutes through the claypan and into the underlying glacial till aquifer. Excess fertilizer N in the unsaturated zone supplied a continuous, but declining input of N to ground water for a period of 15 mo after a single fertilizer application. Calculated solute velocities through the claypan matrix (6.4 x 10-6 cm s-1) were similar to horizontal transport rates along the claypan (3.5 to 7.3 x 10-6 cm s-1) but much slower than infiltration rates determined for preferential flow paths (1.67 x 10-3 cm s-1). These flow paths accounted for 35% of the transport. A seasonally variable, dual mode of transport (matrix and preferential flow) prevented the claypan from being an effective barrier to vertical transport. Simulations of selected field observations, conducted using the variably saturated two- dimensional flow and transport model, VS2DT, confirmed the presence of a dual flow regime in the claypan.

  4. SESOIL. Code System Calculate One-Dimensional Vertical Transport Unsaturated Soil Zone

    SciTech Connect

    Hetrick, D.M.; Scott, D.J.

    1994-08-01

    SESOIL, as an integrated screening-level soil compartment model, is designed to simultaneously model water transport, sediment transport, and pollutant fate. SESOIL is a one-dimensional vertical transport model for the unsaturated soil zone. Only one compound at a time can be considered. The model is based on mass balance and equilibrium partitioning of the chemical between different phases (dissolved, sorbed, vapor, and pure). The SESOIL model was designed to perform long-term simulations of chemical transport and transformations in the soil and uses theoretically derived equations to represent water transport, sediment transport on the land surface, pollutant transformation, and migration of the pollutant to the atmosphere and groundwater. Climatic data, compartment geometry, and soil and chemical property data are the major components used in the equations. SESOIL was developed as a screening-level model, utilizing less soil, chemical, and meteorological values as input than most other similar models. Output of SESOIL includes time-varying pollutant concentrations at various soil depths and pollutant loss from the unsaturated zone in terms of surface runoff, percolation to the groundwater, volatilization, and degradation. The February 1995 release corrects an error that caused the code to fail when average monthly air temperature was -10C and includes an improved iteration procedure for the mass balance equations in the model. PLEASE NOTE: The RISKPRO information management software (see OTHER PROG/OPER SYS INFO) was used by the developers of the New SESOIL User`s Guide in their study and revisions of SESOIL. Using RISKPRO in conjunction with SESOIL is an option, and it may provide the easiest way to use SESOIL. The other option, use of SESOIL in stand-alone mode, has been tested and used. The stand-alone option is covered in `Instructions for Running Stand-Alone SESOIL Code`, and in `A Seasonal Soil Compartment Model`.

  5. Code System Calculate One-Dimensional Vertical Transport Unsaturated Soil Zone

    SciTech Connect

    Bonazountas, Marcos; Wagner, Janet

    1989-03-01

    SESOIL, as an integrated screening-level soil compartment model, is designed to simultaneously model water transport, sediment transport, and pollutant fate. SESOIL is a one-dimensional vertical transport model for the unsaturated soil zone. Only one compound at a time can be considered. The model is based on mass balance and equilibrium partitioning of the chemical between different phases (dissolved, sorbed, vapor, and pure). The SESOIL model was designed to perform long-term simulations of chemical transport and transformations in the soil and uses theoretically derived equations to represent water transport, sediment transport on the land surface, pollutant transformation, and migration of the pollutant to the atmosphere and groundwater. Climatic data, compartment geometry, and soil and chemical property data are the major components used in the equations. SESOIL was developed as a screening-level model, utilizing less soil, chemical, and meteorological values as input than most other similar models. Output of SESOIL includes time-varying pollutant concentrations at various soil depths and pollutant loss from the unsaturated zone in terms of surface runoff, percolation to the groundwater, volatilization, and degradation. The February 1995 release corrects an error that caused the code to fail when average monthly air temperature was -10C and includes an improved iteration procedure for the mass balance equations in the model. PLEASE NOTE: The RISKPRO information management software (see OTHER PROG/OPER SYS INFO) was used by the developers of the New SESOIL User''s Guide in their study and revisions of SESOIL. Using RISKPRO in conjunction with SESOIL is an option, and it may provide the easiest way to use SESOIL. The other option, use of SESOIL in stand-alone mode, has been tested and used. The stand-alone option is covered in ''Instructions for Running Stand-Alone SESOIL Code'', and in ''A Seasonal Soil Compartment Model''.

  6. Code System Calculate One-Dimensional Vertical Transport Unsaturated Soil Zone

    Energy Science and Technology Software Center (ESTSC)

    1989-03-01

    SESOIL, as an integrated screening-level soil compartment model, is designed to simultaneously model water transport, sediment transport, and pollutant fate. SESOIL is a one-dimensional vertical transport model for the unsaturated soil zone. Only one compound at a time can be considered. The model is based on mass balance and equilibrium partitioning of the chemical between different phases (dissolved, sorbed, vapor, and pure). The SESOIL model was designed to perform long-term simulations of chemical transport andmore » transformations in the soil and uses theoretically derived equations to represent water transport, sediment transport on the land surface, pollutant transformation, and migration of the pollutant to the atmosphere and groundwater. Climatic data, compartment geometry, and soil and chemical property data are the major components used in the equations. SESOIL was developed as a screening-level model, utilizing less soil, chemical, and meteorological values as input than most other similar models. Output of SESOIL includes time-varying pollutant concentrations at various soil depths and pollutant loss from the unsaturated zone in terms of surface runoff, percolation to the groundwater, volatilization, and degradation. The February 1995 release corrects an error that caused the code to fail when average monthly air temperature was -10C and includes an improved iteration procedure for the mass balance equations in the model. PLEASE NOTE: The RISKPRO information management software (see OTHER PROG/OPER SYS INFO) was used by the developers of the New SESOIL User''s Guide in their study and revisions of SESOIL. Using RISKPRO in conjunction with SESOIL is an option, and it may provide the easiest way to use SESOIL. The other option, use of SESOIL in stand-alone mode, has been tested and used. The stand-alone option is covered in ''Instructions for Running Stand-Alone SESOIL Code'', and in ''A Seasonal Soil Compartment Model''.« less

  7. Variations in pesticide leaching related to land use, pesticide properties, and unsaturated zone thickness

    USGS Publications Warehouse

    Webb, R.M.T.; Wieczorek, M.E.; Nolan, B.T.; Hancock, T.C.; Sandstrom, M.W.; Barbash, J.E.; Bayless, E.R.; Healy, R.W.; Linard, J.

    2008-01-01

    Pesticide leaching through variably thick soils beneath agricultural fields in Morgan Creek, Maryland was simulated for water years 1995 to 2004 using LEACHM (Leaching Estimation and Chemistry Model). Fifteen individual models were constructed to simulate five depths and three crop rotations with associated pesticide applications. Unsaturated zone thickness averaged 4.7 m but reached a maximum of 18.7 m. Average annual recharge to ground water decreased from 15.9 to 11.1 cm as the unsaturated zone increased in thickness from 1 to 10 m. These point estimates of recharge are at the lower end of previously published values, which used methods that integrate over larger areas capturing focused recharge in the numerous detention ponds in the watershed. The total amount of applied and leached masses for five parent pesticide compounds and seven metabolites were estimated for the 32-km2 Morgan Creek watershed by associating each hectare to the closest one-dimensional model analog of model depth and crop rotation scenario as determined from land-use surveys. LEACHM parameters were set such that branched, serial, first-order decay of pesticides and metabolites was realistically simulated. Leaching is predicted to be greatest for shallow soils and for persistent compounds with low sorptivity. Based on simulation results, percent parent compounds leached within the watershed can be described by a regression model of the form e−depth (a ln t½−b ln KOC) where t 1/2 is the degradation half-life in aerobic soils, K OC is the organic carbon normalized sorption coefficient, and a and b are fitted coefficients (R 2 = 0.86, p value = 7 × 10−9).

  8. Learning from models: Insights into the behavior of water in unsaturated fractured-porous media

    NASA Astrophysics Data System (ADS)

    Ireson, A. M.; Butler, A. P.

    2014-12-01

    The way that water is stored within and transmitted through structured porous media can be challenging to infer from available observation techniques, in particular at field scales. Fractured porous media are an example of such structured media, comprising a fracture domain and a matrix domain. Flow processes depend on how water is both stored and transmitted within each domain, and how water exchanges between the domains. In unsaturated conditions the problem is confounded as hydraulic properties (e.g. hydraulic conductivity) in each domain become dynamic, as a function of saturation. One domain may not contribute significantly to the flow, or may not provide significant amounts of storage, depending of the properties of both domains. The two domains may or may not respond in equilibrium with one another, depending on both the properties and on driving boundary conditions (i.e. infiltration intensity). Physically based models can in theory be used to falsify hypotheses about the role of the fractures versus the matrix in transmitting flow, within an inverse modelling framework. However, there are two problems: firstly, even the most detailed and complex physically based model will still be a simplification of reality, unable to resolve heterogeneities that exist; and secondly the observations available may not contain sufficient information to constrain the model. In this study we explore how models and observations have been applied to understand the flow processes in the unsaturated Chalk in field sites in south east England. We look at what can and cannot be inferred from various observations, including the water table response, soil moisture and matric potential, and the power of these observations to constrain models. We look at how models provide a framework through which to interpret the observations, and provide insights into the dominant controls on behavior. In the case of the unsaturated Chalk, we have demonstrated that groundwater recharge is

  9. Effect of the unsaturated zone thickness on the distribution of water mean transit times in a porous aquifer

    NASA Astrophysics Data System (ADS)

    Schwientek, M.; Maloszewski, P.; Einsiedl, F.

    2009-07-01

    SummaryThe mean transit time of groundwater is commonly expected to increase gradually with increasing depth below water table. The present study provides evidence that the theoretical distribution of transit times may be significantly altered depending on the thickness of the unsaturated zone. An unconfined porous groundwater system formed by Tertiary sediments (Test Field Scheyern close to Munich in southern Germany) is overlain by an unsaturated zone with variable thickness between 4 and 60 m. Between 1992 and 2007 the groundwater system has been repeatedly sampled for tritium contents at different depths using two high-resolved wells. Modelled tritium concentrations by using a lumped parameter approach yielded depth profiles of mean transit times of tracer. In one well the profile was characterized by two local transit time maxima, each of approximately 100 years. A moving particle approach (MPA) developed in this study was used on the streamlines between the recharge zones linked to different sampling depths in the well. This suggested that the observed transit time in the profile was mainly governed by variable travel distances of the tracer through the unsaturated zone at the points of recharge. This finding was confirmed at a second multi-level well of the test site. The lumped parameter modelling of chlorofluorocarbon data yielded lower transit times as compared to those obtained from tritium data. This effect was explained by the different behaviour of tritium and chlorofluorocarbons in the unsaturated zone. The study clearly shows that the impact of a variable thickness of the unsaturated zone may overweigh the effect of local heterogeneities. Such transit time distributions of water in porous aquifers as observed in the present study can only be achieved with the help of environmental tracer data.

  10. The fate and transport of nitroglycerin in the unsaturated zone at active and legacy anti-tank firing positions

    NASA Astrophysics Data System (ADS)

    Bordeleau, Geneviève; Martel, Richard; Ampleman, Guy; Thiboutot, Sonia; Poulin, Isabelle

    2012-11-01

    The environmental fate of nitroglycerin (NG) in the unsaturated zone was evaluated in the context of double-base propellant residue deposition at anti-tank training ranges. Fresh propellant residues were collected during live anti-tank training. Surface soils, sub-surface soils and water samples from the unsaturated zone were collected at an active anti-tank range, and at a legacy site where NG-based propellants have been used. Results show that the residues are composed of intact propellant particles, as well as small quantities of NG, dinitroglycerin (DNG) and nitrate which are rapidly dissolved by precipitation, resulting in sporadic pulses of those compounds in water from the unsaturated zone after rain/snow melt events. The dissolved NG and DNG can be progressively degraded in the unsaturated zone, releasing nitrate as an end-product. Over a period of several years, small propellant particles located at the soil surface can be carried downward through the soil pore system by infiltration water, which explains the presence of NG in sub-surface soils at the legacy site, more than 35 years after site closure. NG is no longer leached from these old particles, therefore the detection of NG in sub-surface soils does not signify that groundwater is at risk of contamination by NG.

  11. Assessment of groundwater quality by unsaturated zone study due to migration of leachate from Abloradjei waste disposal site, Ghana

    NASA Astrophysics Data System (ADS)

    Egbi, Courage Davidson; Akiti, Tetteh Thomas; Osae, Shiloh; Dampare, Samuel Boakye; Abass, Gibrilla; Adomako, Dickson

    2015-06-01

    Leachate generated by open solid waste disposal sites contains substances likely to contaminate groundwater. The impact of potential contaminants migrating from leachate on groundwater can be quantified by monitoring their concentration and soil properties at specific points in the unsaturated zone. In this study, physical and chemical analyses were carried out on leachate, soil and water samples within the vicinity of the municipal solid waste disposal site at Abloradjei, a suburb of Accra, Ghana. The area has seen a massive increase in population and the residents depend on groundwater as the main source of water supply. Results obtained indicate alkaline pH for leachate and acidic conditions for unsaturated zone water. High EC values were recorded for leachate and unsaturated zone water. Major ions (Ca2+, Na+, Mg2+, K+, NO3 -, SO4 2-, Cl-, PO4 3- were analysed in leachate, unsaturated zone water, soil solution and groundwater while trace metals (Al, Fe, Cu, Zn, Pb) were analysed in both soil and extracted soil solution. Concentrations of major ions were high in all samples indicating possible anthropogenic origin. Mean % gravel, % sand, % clay, bulk density, volumetric water content and porosity were 28.8, 63.93, 6.6, 1 g cm-3, 35 and 62.7 %, respectively. Distribution of trace elements showed Kd variation of Al > Cu > Fe > Pb > Zn in the order of sequential increasing solubility. It was observed that the quality of groundwater is not suitable for drinking.

  12. The fate and transport of nitroglycerin in the unsaturated zone at active and legacy anti-tank firing positions.

    PubMed

    Bordeleau, Geneviève; Martel, Richard; Ampleman, Guy; Thiboutot, Sonia; Poulin, Isabelle

    2012-11-01

    The environmental fate of nitroglycerin (NG) in the unsaturated zone was evaluated in the context of double-base propellant residue deposition at anti-tank training ranges. Fresh propellant residues were collected during live anti-tank training. Surface soils, sub-surface soils and water samples from the unsaturated zone were collected at an active anti-tank range, and at a legacy site where NG-based propellants have been used. Results show that the residues are composed of intact propellant particles, as well as small quantities of NG, dinitroglycerin (DNG) and nitrate which are rapidly dissolved by precipitation, resulting in sporadic pulses of those compounds in water from the unsaturated zone after rain/snow melt events. The dissolved NG and DNG can be progressively degraded in the unsaturated zone, releasing nitrate as an end-product. Over a period of several years, small propellant particles located at the soil surface can be carried downward through the soil pore system by infiltration water, which explains the presence of NG in sub-surface soils at the legacy site, more than 35 years after site closure. NG is no longer leached from these old particles, therefore the detection of NG in sub-surface soils does not signify that groundwater is at risk of contamination by NG. PMID:23047138

  13. Tracking sources of unsaturated zone and groundwater nitrate contamination using nitrogen and oxygen stable isotopes at the Hanford Site, WA.

    SciTech Connect

    Singleton, Michael J.; Woods, Katharine N.; Conrad, Mark E.; DePaolo, Donald J.; Dresel, P Evan

    2005-04-15

    The nitrogen and oxygen isotopic compositions of nitrate in pore water extracts from unsaturated zone core samples and groundwater samples indicate at least four potential sources of nitrate plumes in groundwaters at the USDOE Hanford Site in south-central Washington.

  14. A facility designed to monitor the unsaturated zone during infiltration of tertiary-treated sewage, Long Island, New York

    USGS Publications Warehouse

    Prill, Robert C.; Oaksford, Edward T.; Potorti, James E.

    1979-01-01

    A facility consisting of a circular recharge basin 6.10 meters in diameter with a central observation manhole was developed on Long Island, N.Y., to study the role of the unsaturated zone during aquifer recharge with tertiary-treated sewage. The manhole extends through most of the 7.5-meter-thick unsaturated zone, which is composed of glacial outwash sand and gravel, and enables collection of water samples and monitoring of dynamic characteristics of the unsaturated zone during recharge experiments. The system contains instrumentation for monitoring infiltration rate, pressure-head distribution, soil-moisture content, ground-water levels, and soil gases. The 24.55-square-meter recharge basin has operated in all seasons intermittently since April 1975 and, as of April 1978, has transmitted 62 million liters of tertiary-treated effluent to the water-table aquifer. Overall performance of the facility indicates that it is suitably designed for monitoring the unsaturated zone during artificial-recharge experiments. (Kosco-USGS)

  15. Distribution of Minor Elements in Calcite From the Unsaturated Zone at Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Marshall, B. D.; Whelan, J. F.

    2001-12-01

    Calcite is sporadically distributed in fractures and cavities in the volcanic rocks that form the 500- to 700-m-thick unsaturated zone at Yucca Mountain. Previous work has shown that the calcite precipitated from water moving downward through the unsaturated zone since the volcanic rocks were emplaced approximately 13 Ma. Calcite thus serves as a proxy for the chemistry and amounts of past percolation, two parameters that are important in predictions of the future behavior of the potential radioactive waste repository at Yucca Mountain. Latest calcite, which began forming between approximately 5 and 2 Ma, typically displays fine-scale growth zoning defined by distributions of Mn (inferred from cathodoluminescence), Mg, and Sr. Electron microprobe (EPMA) mapping of outermost calcite reveals Mg growth zoning1 and higher overall concentrations of Mg in late calcite than in older calcite. Micro X-ray fluorescence (micro-XRF) maps were obtained by slow rastering of the samples over a 100-watt X-ray source collimated through a final aperture of 100 μ m. Although the spatial resolution of the micro-XRF mapping is much less than that of EPMA, this technique reveals distributions of some elements to which EPMA is less sensitive. Micro-XRF maps show that Sr is spatially correlated with Mg; Sr concentrations range to 500 μ g/g at the resolution of the 100-μ m collimator. Because both Mg and Sr have similar calcite-water distribution coefficients much less than one, the Mg/Sr in calcite reflects the Mg/Sr of the water that precipitated the calcite. The distribution coefficient for Mn is greater than one and variations in Mn are not correlated with Mg and Sr. Covariation of Mg and Sr in the percolating water may be explained by reactions that affect the rate of uptake of chemical constituents from the overlying rock and soil, and/or evaporation. Late calcite has lower δ 13C values, probably due to a regional change from wetter to drier climate conditions. The higher Mg and

  16. Distribution of nitrate in the unsaturated zone, Highland-East Highlands area, San Bernardino County, California

    USGS Publications Warehouse

    Klein, John M.; Bradford, Wesley L.

    1980-01-01

    Nitrogen in the unsaturated soil zone in the Highland-East Highlands area of San Bernardino County, Calif., has been suspected as the source of nitrate in water from wells. Plans to recharge the local aquifers with imported surface water would raise the water table and intercept that nitrogen. This study was made to describe the distribution of inorganic nitrogen and other chemical constituents and nitrogen-using bacteria in the unsaturated zone, to relate nitrogen occurrences, in a general way, to present and historical land use, and to attempt to predict nitrogen concentrations in ground water after recharge. Some generalized correlations between nitrogen occurrence and land use were observed. In 11 of 13 test holes, the maximum nitrate-nitrogen (NO3--N) concentrations occurred within 10 feet of the surface, suggesting that the major source of nitrogen is from the surface at these sites. Test holes were ranked according to maximum NO3--N in the top 10 feet, total NO3--N in the top 10 feet, and total NO3--N in the top 40 feet. In all three rankings, the top seven test holes were the same--five in or near present or historical agricultural areas (primarily citrus groves), one in a feedlot, and one adjacent to an abandoned sewage-treatment plant. Two test holes in historically uninhabited areas ranked lowest. The control test hole in an uninhabited area ranked high in geometric mean of ammonium-nitrogen concentration (NH4+-N), suggesting that present in freshly weathered granite. The geometric means of NH4+-N concentrations in six of eight citrus-related test holes were significantly lower than in the control hole, suggesting that irrigation in citrus groves may have created conditions favoring nitrification of the primary NH4+-N. Rank correlation analyses between various measurements in test holes showed that high NO3--N concentrations tend to occur with high specific conductance and chloride concentrations in soil extracts. If recharge is carried out as planned

  17. Modeling in nuclear waste isolation: Approximate solutions for flow in unsaturated porous media

    SciTech Connect

    Martinez, M.J.; McTigue, D.F.

    1996-12-31

    Mathematical modeling plays a key role in the design and licensing of repositories for radioactive waste. Because safe isolation of nuclear waste involves extremely long time scales, and there exists very little engineering experience upon which to draw, modeling takes on a particularly crucial role. An example of a model problem motivated by hydrological issues in high-level waste isolation is presented. A repository concept involving storage in rock above the water table requires models for the flow of groundwater in unsaturated, porous media. Such flow is governed by an extremely nonlinear diffusion equation, and poses some difficult numerical challenges. A special form of the hydraulic conductivity function however, results in a linear field equation for steady-state problems, for which a boundary integral method yields very fast solutions.

  18. Lattice Boltzmann Modeling of Gaseous Diffusion in Unsaturated Porous Media under Variable Gravity Conditions

    NASA Astrophysics Data System (ADS)

    Chau, J. F.; Or, D.; Jones, S.; Sukop, M.

    2004-05-01

    Liquid distribution in unsaturated porous media under different gravitational forces and resulting gaseous diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. Different fluid behavior in plant growth media under microgravity conditions as compared to earth presents a challenge to plant growth in long duration space exploration missions. Our primary objective was to provide qualitative description and quantitative measures of the role of reduced gravity on hydraulic and gaseous transport properties in simulated porous media. We implemented a multi-phase lattice Boltzmann code for equilibrium distribution of liquid in an idealized two-dimensional porous medium under microgravity and "normal" gravity conditions. The information was then used to provide boundary conditions for simulation of gaseous diffusion through the equilibrium domains (considering diffusion through liquid phase negligibly small). The models were tested by comparison with several analytical solutions to the diffusion equation, with excellent results. The relative diffusion coefficient for both series of simulations (with and without gravity) as functions of air-filled porosity was in good agreement with established models of Millington-Quirk. Liquid distribution under earth's gravity featured increased water content at the lower part of the medium relative to the distribution in reduced gravity, which resulted in decreased gas diffusion through a vertically oriented column of a porous medium. Simulation results for larger domains under various orientations will be presented.

  19. Salt Precipitation and Dissolution in an Unsaturated Porous Media Under Non-Isothermal Conditions

    NASA Astrophysics Data System (ADS)

    Burns, E. R.; Dragila, M. I.; Weisbrod, N.; Guenther, R. B.; Selker, J. S.

    2003-12-01

    Salt precipitation and dissolution in unsaturated porous media is an important process to understand, both for agricultural soils (fertilizer movement) and for its effects in controlling water flux and potential contaminant transport in arid regions (migration of fluids and solutes to fractures and the land surface). Since evaporation is a key process to consider in both scenarios, it is necessary to consider heat and energy flow. A brief discussion/history of the salt precipitation/dissolution problem is given, then using the principles of continuum mechanics and mixture theory, a set of governing equations for salt precipitation and dissolution is developed. The equations are general in the sense that the following are considered: 1) non-isothermal conditions; 2) porosity is a function of solid phase salt concentration; 3) all parameters are functions of the appropriate thermodynamic variables. The equations are limited in that only near-ground surface conditions are considered. This is generally not a serious limitation since this location is likely the most seriously affected by rapid temporal changes in temperature and other boundary conditions. Further simplification of the problem is achieved by considering only "simple" salts (defined here as non-pH buffered salts that dissolve/precipitate only as a function of liquid phase ionic concentration) and flow regimes that do not result in finger flow of liquids. Initial and boundary conditions are developed for the following physically relevant conditions: 1) fertilizer salts introduced to an initially wet (but unsaturated) soil; 2) salt formation on free surfaces in arid climates; 3) water imbibition of fresh water into saline porous media. Work to date on solution of the initial boundary value problems is presented.

  20. Cotransport of viruses and clay particles in water saturated and unsaturated porous media

    NASA Astrophysics Data System (ADS)

    Chrysikopoulos, C. V.; Syngouna, V. I.

    2014-12-01

    This experimental study examines the effects of clay colloids on the transport of viruses in variably saturated porous media. All cotransport experiments were conducted in both saturated and partially saturated columns packed with glass beads, using bacteriophages MS2 and ΦΧ174 as model viruses, and kaolinite (KGa-1b) and montmorillonite (STx-1b) as model clay colloids. The various experimental collision efficiencies were determined using the classical colloid filtration theory. The experimental data indicated that the mass recovery of viruses and clay colloids decreased as the water saturation decreased. Temporal moments of the various breakthrough concentrations collected, suggested that the presence of clays significantly influenced virus transport and irreversible deposition onto glass beads. The mass recovery of both viruses, based on total effluent virus concentrations, was shown to reduce in the presence of suspended clay particles. Furthermore, the transport of suspended virus and clay-virus particles was retarded, compared to the conservative tracer. Under unsaturated conditions both clay particles hindered the transport of the two viruses considered in this work. Moreover, the surface properties of viruses, clays and glass beads were employed for the construction of classical DLVO and capillary potential energy profiles, and the results suggested that capillary forces play a significant role on colloid retention. It was estimated that the capillary potential energy of MS2 is lower than that of ΦΧ174, and the capillary potential energy ofKGa-1b is lower than that of STx-1b, assuming that the protrusion distance through the water filmis the same for each pair of particles. Moreover, the capillary potential energy is several orders of magnitude greater than the DLVO energy potential. Figure 1Schematic illustration of the various concentrations involved in the cotransport experiments for: (a) saturated and (b) unsaturated porous media.

  1. Distribution of nitrate and related nitrogen species in the unsaturated zone, Redlands and vicinity, San Bernardino County, California

    USGS Publications Warehouse

    Klein, John M.; Bradford, Wesley L.

    1979-01-01

    Nitrogen in the unsaturated soil zone in the vicinity of Redlands in San Bernardino County, Calif., has been suspected as the source of nitrate in water from wells. Plans have been made to recharge the aquifer with imported surface water. If this occurs, the rising water table will intercept soluble nitrate in the unsaturated zone. This study was made to quantify and delineate the distribution of the nitrate in the unsaturated zone. Thirteen test holes were drilled in areas of various land uses, and samples of the unsaturated-zone materials were obtained with depth. In 10 of the test holes, the maximum nitrate-nitrogen (N03--N) concentrations occurred within 10 feet of land surface suggesting N03--N sources at the surface. Ranking the test holes according to near-surface N03--N concentrations showed that, of the top six, only two are in irrigated citrus areas. One is in an abandoned feedlot. Of the lowest six, four are in irrigated citrus areas and one is in the Santa Ana River channel. The control test hole ranked fourth suggesting that relatively high N03--N concentrations can occur in near-surface soils even in the absence of human habitation. Analysis according to one conceptual model suggests that raising the water-table altitude by aquifer recharge will intercept N03--N now in the unsaturated zone causing increases in N03--N concentrations in water from wells of up to 48 milligrams per liter. The largest increases will occur in the vicinity of irrigated citrus areas. (Woodard-USGS).

  2. Using chloride to trace water movement in the unsaturated zone at Yucca Mountain

    SciTech Connect

    Fabryka-Martin, J.T.; Winters, S.T.; Wolfsberg, A.V.; Wolfsberg, L.E.; Roach, J.L.

    1998-12-31

    The nonwelded Paintbrush Tuff (PTn) hydrogeologic unit is postulated as playing a critical role in the redistribution of moisture in the unsaturated zone at Yucca Mountain, Nevada. Fracture-dominated flow in the overlying low-permeability, highly fractured Tiva Canyon welded (TCw) unit is expected to transition to matrix-dominated flow in the high-permeability, comparatively unfractured PTn. The transition process from fracture to matrix flow in the PTn, as well as the transition from low to high matrix storage capacity, is expected to damp out most of the seasonal, decadal, and secular variability in surface infiltration. This process should also result in the homogenization of the variable geochemical and isotopic characteristics of pore water entering the top of the PTn. In contrast, fault zones that provide continuous fracture pathways through the PTn may damp climatic and geochemical variability only slightly and may provide fast paths from the surface to the sampled depths, whether within the PTn or in underlying welded tuffs. Chloride (Cl) content and other geochemical data obtained from PTn pore-water samples can be used to independently derive infiltration rates for comparison with surface infiltration estimates, to evaluate the role of structural features as fast paths, and to assess the prevalence and extent to which water may be laterally diverted in the PTn due to contrasting hydrologic properties of its subunits.

  3. Unsaturated zone carbon dioxide flux, mixing, and isotopic composition at the USGS Amargosa Desert Research Site

    NASA Astrophysics Data System (ADS)

    Conaway, C. H.; Thordsen, J. J.; Thomas, B.; Haase, K.; Moreo, M. T.; Walvoord, M. A.; Andraski, B. J.; Stonestrom, D. A.

    2015-12-01

    Elevated concentrations of tritium, radiocarbon, and volatile organic compounds at the USGS Amargosa Desert Research Site, adjacent to a low-level radioactive waste disposal facility, have stimulated research on factors affecting transport of these contaminants. This research includes an examination of unsaturated zone carbon dioxide (CO2) fluxes, mixing, and isotopic composition, which can help in understanding these factors. In late April 2015 we collected 76 soil-gas samples in multi-layer foil bags from existing 1.5-m deep tubes, both inside and outside the low-level waste area, as well as from two 110-m-deep multilevel gas-sampling boreholes and a distant background site. These samples were analyzed for carbon dioxide concentration and isotopic composition by direct injection into a cavity ring-down spectrometer. Graphical analysis of results indicates mixing of CO2 characteristic of the root zone (δ13C -18 ‰ VPDB), deep soil gas of the capillary fringe (-20‰), and CO2 produced by microbial respiration of organic matter disposed in the waste area trenches (-28‰). Land-surface boundary conditions are being constrained by the application of a novel non-dispersive infrared sensor and traditional concentration and flux measurements, including discrete CO2 flux data using a gas chamber method to complement continuous data from surface- and tower-based CO2 sensors. These results shed light on radionuclide and VOC mobilization and transport mechanisms from this and similar waste disposal facilities.

  4. USING CHLORIDE TO TRACE WATER MOVEMENT IN THE UNSATURATED ZONE AT YUCCA MOUNTAIN

    SciTech Connect

    Fabryka-Martin, J. T.; Flint, L. E.; Wolfsberg, A. V.; Sweetking, D. S.; Hudson, D.; Roach, J. L.; Winters, S. T.; Wolfsberg, L. E.

    1998-01-08

    The nonwelded Paintbrush Tuff (PTn) hydrogeologic unit is postulated as playing a critical role in the redistribution of moisture in the unsaturated zone at Yucca Mountain, Nevada. Fracture-dominated flow in the overlying low-permeability, highly fractured Tiva Canyon welded (TCw) unit is expected to transition to matrix-dominated flow in the high-permeability, comparatively unfractured PTn. The transition process from fracture to matrix flow in the PTn, as well as the transition from low to high matrix storage capacity, is expected to damp out most of the seasonal, decadal, and secular variability in surface infiltration. This process should also result in the homogenization of the variable geochemical and isotopic characteristics of pore water entering the top of the PTn. In contrast, fault zones that provide continuous fracture pathways through the PTn may damp climatic and geochemical variability only slightly and may provide fast paths from the surface to the sampled depths, whether within the PTn or in underlying welded tuffs. Chloride (Cl) content and other geochemical data obtained from PTn pore water samples can be used to independently derive infiltration rates for comparison with surface infiltration estimates, to evaluate the role of structural features as fast paths, and to assess the prevalence and extent to which water may be laterally diverted in the PTn due to contrasting hydrologic properties of its subunits.

  5. Chlorine-36 data at Yucca Mountain: Statistical tests of conceptual models for unsaturated-zone flow

    USGS Publications Warehouse

    Campbell, K.; Wolfsberg, A.; Fabryka-Martin, J.; Sweetkind, D.

    2003-01-01

    An extensive set of chlorine-36 (36Cl) data has been collected in the Exploratory Studies Facility (ESF), an 8-km-long tunnel at Yucca Mountain, Nevada, for the purpose of developing and testing conceptual models of flow and transport in the unsaturated zone (UZ) at this site. At several locations, the measured values of 36Cl/Cl ratios for salts leached from rock samples are high enough to provide strong evidence that at least a small component of bomb-pulse 36Cl, fallout from atmospheric testing of nuclear devices in the 1950s and 1960s, was measured, implying that some fraction of the water traveled from the ground surface through 200-300 m of unsaturated rock to the level of the ESF during the last 50 years. These data are analyzed here using a formal statistical approach based on log-linear models to evaluate alternative conceptual models for the distribution of such fast flow paths. The most significant determinant of the presence of bomb-pulse 36Cl in a sample from the welded Topopah Spring unit (TSw) is the structural setting from which the sample was collected. Our analysis generally supports the conceptual model that a fault that cuts through the nonwelded Paintbrush tuff unit (PTn) that overlies the TSw is required in order for bomb-pulse 36Cl to be transmitted to the sample depth in less than 50 years. Away from PTn-cutting faults, the ages of water samples at the ESF appear to be a strong function of the thickness of the nonwelded tuff between the ground surface and the ESF, due to slow matrix flow in that unit. ?? 2002 Elsevier Science B.V. All rights reserved.

  6. Stratigraphy of the unsaturated zone at the radioactive waste management complex, Idaho National Engineering Laboratory, Idaho

    USGS Publications Warehouse

    Anderson, S.R.; Lewis, B.D.

    1989-01-01

    A complex sequence of layered basalt flows, cinders, and sediment underlies the Radioactive Waste Management Complex at the Idaho National Engineering Laboratory in southeastern Idaho. Wells drilled to 700 ft penetrate a sequence of 10 basalt-flow groups and 7 major sedimentary interbeds that range in age from about 100,000 to 600,000 years old. The 10 flow groups consist of 22 separate lava flows and flow-units. Each flow group is made up of from one to five petrographically similar flows that erupted from common source areas during periods of less than 200 years. Sedimentary interbeds consist of fluvial, lacustrine, and wind-blown deposits of clay, silt, sand, and gravel that accumulated during periods of volcanic inactivity ranging from thousands to hundreds of thousands of years. Flows and sediment are unsaturated to a depth of about 600 ft. Flows and sediment below a depth of 600 ft are saturated and make up the uppermost part of the Snake River Plain aquifer. The areal extent of flow groups and interbeds was determined from well cuttings, cores, geophysical logs, potassium-argon ages, and geomagnetic properties. Stratigraphical control was provided by four sequential basalt flows near the base of the unsaturated zone that have reversed geomagnetic polarity and high emission of natural gamma radiation compared to other flows. Natural gamma logs were used as a primary correlation tool. Natural-gamma emissions, which are generally uniform in related, petrographically similar flows, increase or decrease between petrographically dissimilar flows of different age and source. (USGS)

  7. Chlorine-36 data at Yucca Mountain: statistical tests of conceptual models for unsaturated-zone flow.

    PubMed

    Campbell, Katherine; Wolfsberg, Andrew; Fabryka-Martin, June; Sweetkind, Donald

    2003-01-01

    An extensive set of chlorine-36 (36Cl) data has been collected in the Exploratory Studies Facility (ESF), an 8-km-long tunnel at Yucca Mountain, Nevada, for the purpose of developing and testing conceptual models of flow and transport in the unsaturated zone (UZ) at this site. At several locations, the measured values of 36Cl/Cl ratios for salts leached from rock samples are high enough to provide strong evidence that at least a small component of bomb-pulse 36Cl, fallout from atmospheric testing of nuclear devices in the 1950s and 1960s, was measured, implying that some fraction of the water traveled from the ground surface through 200-300 m of unsaturated rock to the level of the ESF during the last 50 years. These data are analyzed here using a formal statistical approach based on log-linear models to evaluate alternative conceptual models for the distribution of such fast flow paths. The most significant determinant of the presence of bomb-pulse 36Cl in a sample from the welded Topopah Spring unit (TSw) is the structural setting from which the sample was collected. Our analysis generally supports the conceptual model that a fault that cuts through the nonwelded Paintbrush tuff unit (PTn) that overlies the TSw is required in order for bomb-pulse 36Cl to be transmitted to the sample depth in less than 50 years. Away from PTn-cutting faults, the ages of water samples at the ESF appear to be a strong function of the thickness of the nonwelded tuff between the ground surface and the ESF, due to slow matrix flow in that unit. PMID:12714284

  8. Characterization of liquid-water percolation in tuffs in the unsaturated zone, Yucca Mountain, Nye County, Nevada

    SciTech Connect

    Kume, J.; Rousseau, J.P.

    1989-12-31

    A surface-based borehole investigation currently (1989) is being done to characterize liquid-water percolation in tuffs of Miocene age in the unsaturated zone beneath Yucca Mountain, Nye County, Nevada Active in-situ testing and passive in-situ monitoring will be used in this investigation to estimate the present-day liquid-water percolation (flux). The unsaturated zone consists of a gently dipping sequence of fine-grained, densely fractured, and mostly welded ash-flow tuffs that are interbedded with fine-grained, slightly fractured, non-welded ash-flow and ash-fall tuffs that are partly vitric and zeolitized near the water table. Primary study objectives are to define the water potential field within the unsaturated zone and to determine the in-situ bulk permeability and bulk hydrologic properties of the unsaturated tuffs. Borehole testing will be done to determine the magnitude and spatial distribution of physical and hydrologic properties of the geohydrologic units, and of their water potential fields. The study area of this investigation is restricted to that part of Yucca Mountain that immediately overlies and is within the boundaries of the perimeter drift of a US Department of Energy proposed mined, geologic, high-level radioactive-waste repository. Vertically, the study area extends from near the surface of Yucca Mountain to the underlying water table, about 500 to 750 meters below the ground surface. The average distance between the proposed repository and the underlying water table is about 205 meters.

  9. Diffusion and consumption of methane in an unsaturated zone in north-central Illinois, U.S.A.

    USGS Publications Warehouse

    Striegl, R.G.; Ishii, A.L.

    1989-01-01

    The distribution of CH4 in unsaturated glacial and eolian deposits adjacent to buried low-level radioactive waste was measured, and movement of the gas from the waste source was simulated using a two-dimensional finite-difference model for gas diffusion in the unsaturated zone. Mean PCH4 was greatest (1.56 Pa) in a pebbly-sand deposit 11.6 m below the land surface and 12 m from the waste, and generally decreased with increased horizontal distance from the waste. Mean PCH4 was least (0.07 Pa) at depth of 1.8 m below land surface, regardless of distance from the waste. PCH4 at the land surface averaged 0.17 Pa. Depth versus PCH4 profiles suggest consumption of both waste-produced and atmospheric CH4 in the upper unsaturated zone, presumably by methanotrophic microorganisms. Numerical simulations of methane movement support the consumption observation; inclusion of a term in the model for consumption of CH4 in the upper 2 m of the unsaturated zone resulted in simulated PCH4 within 30% of mean PCH4 at eleven of thirteen sampling locations. A similar fit of the data was obtained for only four locations when consumption was not considered. ?? 1989.

  10. Methodology, results, and significance of an unsaturated-zone tracer test at an artificial-recharge facility, Tucson, Arizona

    USGS Publications Warehouse

    Graham, D.D.

    1989-01-01

    A tracer test conducted in 1987 at an artificial-recharge facility in Tucson, Arizona, indicates that solute movement through the poorly sorted stratified alluvial sediments in the unsaturated zone beneath a recharge basin takes place along preferential-flow paths. Movement of a tracer-laced pulse of reclaimed wastewater was monitored using pressure-vacuum lysimeters installed at depths that range from 11 to 45 ft below the bottom of the recharge basin. Tracer-breakthrough curves do not indicate a consistent relation between maximum tracer concentration and depth or between time of tracer breakthrough and depth. Apparent dispersion, as indicated by the slope of the rising leg of the tracer-breakthrough curve, shows no apparent relation with depth. In some cases, the tracer arrived earlier at deep sampling locations than at shallow ones. Velocity of solute flow ranged from 1.9 to 9.0 ft/day. Less interaction between recharge water and solid-phase materials in the unsaturated zone occurs under preferential-flow conditions than if flow occurred as a uniform wetting front. Flow of water through the unsaturated zone is concentrated into fingers or channels under preferential-flow conditions, and the renovating capability of soil is reduced because of the reduced surface area and reduced contact time in the biologically active part of the unsaturated profile. Chemical substances that normally would be decomposed by microbial activity or sorbed by sediment particles can move through the unsaturated zone and cause groundwater contamination under preferential-flow conditions. (USGS)

  11. Evaluating Ecosystem Services for Reducing Groundwater Nitrate Contamination: Nitrate Attenuation in the Unsaturated and Saturated Zones

    NASA Astrophysics Data System (ADS)

    Wang, J.

    2013-12-01

    Nitrates are the most common type of groundwater contamination in agricultural regions. Environmental policies targeting nitrates have focused on input control (e.g., restricted fertilizer application), intermediate loads control (e.g., reduce nitrate leached from crop fields), and final loads control (e.g., reduce catchment nitrate loads). Nitrate loads can be affected by hydrological processes in both unsaturated and saturated zones. Although many of these processes have been extensively investigated in literature, they are commonly modeled as exogenous to farm management. A couple of recent studies by scientists from the Lawrence Livermore National Laboratory show that in some situations nitrate attenuation processes in the unsaturated/saturated zone, particularly denitrification, can be intensified by certain management practices to mitigate nitrate loads. Therefore, these nitrate attenuation processes can be regarded as a set of ecosystem services that farmers can take advantage of to reduce their cost of complying with environmental policies. In this paper, a representative California dairy farm is used as a case study to show how such ecosystem attenuation services can be framed within the farm owner's decision-making framework as an option for reducing groundwater nitrate contamination. I develop an integrated dynamic model, where the farmer maximizes discounted net farm profit over multiple periods subject to environmental regulations. The model consists of three submodels: animal-waste-crop, hydrologic, and economic model. In addition to common choice variables such as irrigation, fertilization, and waste disposal options, the farmer can also endogenously choose from three water sources: surface water, deep groundwater (old groundwater in the deep aquifer that is not affected by farm effluent in the short term), and shallow groundwater (drainage water that can be recycled via capture wells at the downstream end of the farm). The capture wells not only

  12. Seismoelectric coupling in unsaturated porous media: theory, petrophysics, and saturation front localization using an electroacoustic approach

    NASA Astrophysics Data System (ADS)

    Revil, A.; Barnier, G.; Karaoulis, M.; Sava, P.; Jardani, A.; Kulessa, B.

    2014-02-01

    The seismoelectric method is based on the interpretation of the electrical field associated with the conversion of mechanical to electromagnetic energy during the propagation of seismic waves in heterogeneous porous media. We propose an extension of a poroacoustic model that takes into account fluid flow and the effect of saturation. This model is coupled with an electrokinetic model accounting for the effect of saturation and in agreement with available experimental data in sands and carbonate rocks. We also developed new scaling laws for the permeability, the streaming potential coupling coefficient and the capillary entry pressure of porous media. The theory is developed for frequencies much below the critical frequency at which inertial effects starts to dominate in the Navier-Stokes equation (>10 kHz). The equations used to compute the propagation of the P waves and the seismoelectric effect in unsaturated condition are solved with finite elements using triangular meshing. We demonstrate the usefulness of a recently developed technique, seismoelectric beamforming, to localize saturation fronts by focusing seismic waves and looking at the resulting seismoelectric conversions. This method is applied to a cross-hole problem showing how a saturation front characterized by a drop in the electrical conductivity and compressibility is responsible for seismoelectric conversions. These conversions can be used, in turn, to determine the position of the front over time.

  13. Influence of the Gas-Water Interface on Transport of Microorganisms through Unsaturated Porous Media

    PubMed Central

    Wan, Jiamin; Wilson, John L.; Kieft, Thomas L.

    1994-01-01

    In this article, a new mechanism influencing the transport of microorganisms through unsaturated porous media is examined, and a new method for directly visualizing bacterial behavior within a porous medium under controlled chemical and flow conditions is introduced. Resting cells of hydrophilic and relatively hydrophobic bacterial strains isolated from groundwater were used as model microorganisms. The degree of hydrophobicity was determined by contact-angle measurements. Glass micromodels allowed the direct observation of bacterial behavior on a pore scale, and three types of sand columns with different gas saturations provided quantitative measurements of the observed phenomena on a porous medium scale. The reproducibility of each break-through curve was established in three to five repeated experiments. The data collected from the column experiments can be explained by phenomena directly observed in the micromodel experiments. The retention rate of bacteria is proportional to the gas saturation in porous media because of the preferential sorption of bacteria onto the gas-water interface over the solid-water interface. The degree of sorption is controlled mainly by cell surface hydrophobicity under the simulated groundwater conditions because of hydrophobic forces between the organisms and the interfaces. The sorption onto the gas-water interface is essentially irreversible because of capillary forces. This preferential and irreversible sorption at the gas-water interface strongly influences the movement and spatial distribution of microorganisms. Images PMID:16349180

  14. Density-Driven Migration of Heavy NAPL Vapor in the Unsaturated Zone

    NASA Astrophysics Data System (ADS)

    Kleinknecht, S. M.; Class, H.; Braun, J.

    2014-12-01

    Contamination of the subsoil is a major concern in industrially developed as well as developing countries. Liquids introduced into the unsaturated zone will migrate as a liquid phase, however, they will also vaporize and migrate in a gaseous state. In particular, vapor (gas) plumes migrate easily in the unsaturated zone. Heavy vapors migrate, preferentially downward, due to their greater density and thus pose a potential threat to aquifers. Large scale column experiments and numerical simulations were conducted to investigate migration of carbon disulfide vapor. Carbon disulfide (CS2), amongst others used for the manufacture of viscous rayon, is an industrial, non-polar solvent. It is highly volatile and characterized by a higher density than water (ρ = 1.263 g/cm3) and, above all, denser than air when in a gaseous state (1.6 compared to air). The goals of these investigations were to quantitatively describe density-driven vapor migration in the subsurface at a large scale with clearly defined and controlled boundary conditions. The experiments were conducted in vertical, large columns (ID = 0.109 m) of 4 m length packed with dry porous medium in which the migration behavior of CS2vapor was characterized. Different types of glass beads were used to investigate the influence of permeability. The porous medium was kept dry to avoid partitioning effects due to pore water. The upper and lower boundaries were open to the atmosphere and hence constant pressure boundaries which allowed for an unhindered migration of the heavy vapor injected in the middle section of the column. Gas samples were taken along the column throughout the experiment and analyzed using a GC (HP 6890 Series) to quantify time and space dependent migration. The set-up of the experiment was numerically reproduced employing a 1-D, two-phase, two-component, isothermal model. Simulation results were compared with data from vapor migration experiments to verify the model. Variations were performed to

  15. Design of a three-dimensional site-scale model for the unsaturated zone at Yucca Mountain, Nevada

    SciTech Connect

    Wittwer, C.S.; Bodvarsson, G.S.; Chornack, M.P.; Flint, A.L.; Lewis, B.D.; Spengler, R.W.; Flint, L.E.; Rautman, C.A.

    1992-01-01

    A three-dimensional model of moisture flow within the unsaturated zone at Yucca Mountain is being developed. This site-scale model covers an area of about 30 km{sup 2} and is bounded by major faults to the east and west. A detailed numerical grid has been developed based on location of boreholes, different infiltration zones, hydrogeological units and their outcrops, major faults, and water level data. Different maps, such as contour maps and isopachs maps, are presented for the different infiltration zones, and for the base of the Tiva Canyon, the Paintbrush, and the Topopah Spring hydrogeological units.

  16. Design of a three-dimensional site scale model for the unsaturated zone at Yucca Mountain, Nevada

    SciTech Connect

    Wittwer, C.S.; Bodvarsson, G.S.; Chornack, M.P.; Flint, A.L.; Lewis, B.D.; Spengler, R.W.; Flint, L.E.; Rautman, C.A.

    1992-10-01

    This paper discusses a three-dimensional model of moisture flow within the unsaturated zone at Yucca Mountain which is being developed. The site-scale model covers an area of about 30 km{sup 2} and is bounded by major faults to the east and west. A detailed numerical grid has been developed based on locations of boreholes, different infiltration zones, hydrogeological units and their outcrops, major faults, and water level data. Different maps, such as contour maps and isopachs maps, are presented for the different infiltration zones, and for the base of the Tiva Canyon, the Paintbrush, and the Topopah Spring hydrogeological units.

  17. Geostatistical and Stochastic Study of Flow and Transport in the Unsaturated Zone at Yucca Mountain

    SciTech Connect

    Ye, Ming; Pan, Feng; Hu, Xiaolong; Zhu, Jianting

    2007-08-14

    Yucca Mountain has been proposed by the U.S. Department of Energy as the nation’s long-term, permanent geologic repository for spent nuclear fuel or high-level radioactive waste. The potential repository would be located in Yucca Mountain’s unsaturated zone (UZ), which acts as a critical natural barrier delaying arrival of radionuclides to the water table. Since radionuclide transport in groundwater can pose serious threats to human health and the environment, it is important to understand how much and how fast water and radionuclides travel through the UZ to groundwater. The UZ system consists of multiple hydrogeologic units whose hydraulic and geochemical properties exhibit systematic and random spatial variation, or heterogeneity, at multiple scales. Predictions of radionuclide transport under such complicated conditions are uncertain, and the uncertainty complicates decision making and risk analysis. This project aims at using geostatistical and stochastic methods to assess uncertainty of unsaturated flow and radionuclide transport in the UZ at Yucca Mountain. Focus of this study is parameter uncertainty of hydraulic and transport properties of the UZ. The parametric uncertainty arises since limited parameter measurements are unable to deterministically describe spatial variability of the parameters. In this project, matrix porosity, permeability and sorption coefficient of the reactive tracer (neptunium) of the UZ are treated as random variables. Corresponding propagation of parametric uncertainty is quantitatively measured using mean, variance, 5th and 95th percentiles of simulated state variables (e.g., saturation, capillary pressure, percolation flux, and travel time). These statistics are evaluated using a Monte Carlo method, in which a three-dimensional flow and transport model implemented using the TOUGH2 code is executed with multiple parameter realizations of the random model parameters. The project specifically studies uncertainty of unsaturated

  18. Physicochemical controls on absorbed water film thickness in unsaturated geological media

    SciTech Connect

    Tokunaga, T.

    2011-06-14

    Adsorbed water films commonly coat mineral surfaces in unsaturated soils and rocks, reducing flow and transport rates. Therefore, it is important to understand how adsorbed film thickness depends on matric potential, surface chemistry, and solution chemistry. Here, the problem of adsorbed water film thickness is examined through combining capillary scaling with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Novel aspects of this analysis include determining capillary influences on film thicknesses, and incorporating solution chemistry-dependent electrostatic potential at air-water interfaces. Capillary analysis of monodisperse packings of spherical grains provided estimated ranges of matric potentials where adsorbed films are stable, and showed that pendular rings within drained porous media retain most of the 'residual' water except under very low matric potentials. Within drained pores, capillary contributions to thinning of adsorbed films on spherical grains are shown to be small, such that DLVO calculations for flat surfaces are suitable approximations. Hamaker constants of common soil minerals were obtained to determine ranges of the dispersion component to matric potential-dependent film thickness. The pressure component associated with electrical double layer forces was estimated using the compression and linear superposition approximations. The pH-dependent electrical double layer pressure component is the dominant contribution to film thicknesses at intermediate values of matric potential, especially in lower ionic strength solutions (< 10 mol m{sup -3}) on surfaces with higher magnitude electrostatic potentials (more negative than - 50 mV). Adsorbed water films are predicted to usually range in thickness from 1 to 20 nm in drained pores and fractures of unsaturated environments.

  19. Surfactant-Induced Flow in Unsaturated Porous Media: Implications for Air-Water Interfacial Area Determination

    NASA Astrophysics Data System (ADS)

    Costanza-Robinson, M. S.; Zheng, Z.; Estabrook, B.; Henry, E. J.; Littlefield, M. H.

    2011-12-01

    Air-water interfacial area (AI) in porous media is an important factor governing equilibrium contaminant retention, as well as the kinetics of interphase mass transfer. Interfacial-partitioning tracer (IPT) tests are a common technique for measuring AI at a given moisture saturation (SW), where AI is calculated based on the ratio of arrival times of a surfactant and a non-reactive tracer. At surfactant concentrations often used, the aqueous surface tension of the interfacial tracer solution is ~30% lower than that of the resident porewater in the system, creating transient surface tension gradients during the IPT measurement. Because surface tension gradients create capillary pressure gradients, surfactant-induced unsaturated flow may occur during IPT tests, a process that would violate fundamental assumptions of constant SW, of steady-state flow, and of nonreactive and surfactant tracers experiencing the same transport conditions. To examine the occurrence and magnitude of surfactant-induced flow, we conducted IPT tests for unsaturated systems at ~84% initial SW using surfactant input concentrations that bracket concentrations commonly used. Despite constant boundary conditions (constant inlet flux and outlet pressure), the introduction of the surfactant solution induced considerable transience in column effluent flowrate and SW. Real-time system mass measurements revealed drainage of 20-40% SW, with the amount of drainage and the maximum rate of drainage proportional to the influent surfactant concentration, as would be expected. Because AI is inversely related to SW, the use of higher surfactant concentrations should yield larger AI estimates. Measured AI values, however, showed no clear relationship to surfactant concentration or the time-averaged SW of the system. These findings cast doubt on the reliability of IPT for AI determination.

  20. Influence of soil structure and root water uptake strategy on unsaturated flow in heterogeneous media

    NASA Astrophysics Data System (ADS)

    Kuhlmann, A.; Neuweiler, I.; van der Zee, S. E. A. T. M.; Helmig, R.

    2012-02-01

    We analyze the combined effects of the spatial variability of soil hydraulic properties and the water uptake by plant roots on unsaturated water flow. For this analysis, we use a simplified macroscopic root water uptake model which is usually applied only for homogeneous or layered soil and therefore we also determine whether it is applicable for multidimensional heterogeneous media. Analytical solutions for mean and variance of pressure head (first-order second-moment approximations) in layered media and numerical solutions of two-dimensional (2-D) autocorrelated multi-Gaussian and non multi-Gaussian parameter fields are analyzed for steady state and transient flow conditions. For non-Gaussian topological features, that have little influence on the mean and the variance of the pressure field if root water uptake is ignored, we test whether the influence is significant if root water uptake is accounted for. The results reveal that, in field structures with large patches of coarse material, local regions with pressure head values at the wilting point develop; these are surrounded by wet material. Without a compensation mechanism for local stress, the global transpiration demand is not met if local wilting occurs. Various compensation mechanisms are tested that depend, respectively, on the saturation, the relative conductivity or a strategy where the deficit in the global uptake rate is equally distributed to unstressed locations. The strategies lead to a global actual transpiration rate at the potential value and attenuate the formation of locally wilted areas. Wilted regions can, however, still occur, and may be an artifact of the simplified model concept as root-soil interactions are neglected. Therefore simplified macroscopic models for root water uptake should be used with caution in heterogeneous media.

  1. Assessment of unsaturated zone radionuclide contamination in the 200 areas of the Hanford site, Washington

    SciTech Connect

    Brodeur, J.R.; Wittreich, C.D.

    1993-03-01

    The 200 East and 200 West Areas at the Department of Energy`s Hanford site in southeastern Washington, contain chemical and nuclear fuel processing facilities that disposed of large volumes of chemical and radionuclide effluents to the ground via various structures such as ponds, cribs and ditches. A geophysical logging investigation was implemented in 1992 to assess the nature and extent of contamination beneath select liquid disposal sites in the 200 Areas. The borehole geophysical logging was accomplished with a recently developed spectral gamma-ray logging system called the Radionuclide Logging System (RLS). This system has a high-resolution, intrinsic germanium detector mounted in a downhole probe and is calibrated and operated specifically for use in a borehole environment. It provides a means to develop in-situ, gamma-emitting radioelement concentration profiles. Approximately 50 boreholes were logged in this study. The RLS log data provided information about the migration and deposition patterns of specific radionuclides in the unsaturated zone and their impacts on the groundwater. Approximately 10 radionuclide species were detected and quantified. Results of the field investigation are being used to refine site specific conceptual models, support Hanford Site remediation decisions and focus future characterization activities.

  2. Synopsis of recent moisture flux analyses relevant to the unsaturated zone at Area G

    SciTech Connect

    Vold, E.

    1998-03-01

    This report summarizes selected recent analyses relevant to the assessment of the site performance for disposal facilities at Los Alamos (Area G) regarding unsaturated zone transport of moisture in liquid and vapor phases and the surface water balance. Much of the analyses methods have been reported previously but in several separate and detailed reports. These do not always reflect the overview possible with hindsight. The present report is an attempt to integrate the author`s previous results into a cohesive whole. Due to project time constraints, this report is incomplete in some area. This report first reviews the basis for the Darcy flux analyses and its inherent uncertainties, as detailed in previous reports. Results from the previous works are then reviewed and discussed and in some cases, elaborated in an attempt for clarification. New results of the Darcy Flux Analyses are presented and discussed for Area G mesa top locations, nearby canyon locations and a second mesa top location (TA46 west of Area G). Select evapotranspiration and precipitation data from TA6 are presented and discussed. The conclusions section draws a picture of the hydrology which unifies the study results reported here and in previous reports for the undisturbed and disturbed site locations.

  3. UNSATURATED ZONE CALCITE 813C EVIDENCE OF SOUTHERN NEVADA CLIMATES DURING THE PAST 9 MILLION YEARS

    SciTech Connect

    JOSEPH F. WHELAN AND RICHARD J. MOSCATI

    1998-01-26

    Yucca Mountain, Nevada, is presently the object of intense study as a potential permanent repository for the Nation's high-level radioactive wastes. The mountain consists of a thick sequence of volcanic tuffs in which the depth to the water table ranges from 500 to 700 meters below the land surface. This thick unsaturated zone (UZ), which would host the projected repository, coupled with the present-day arid to semi-arid environment, is considered a positive argument for the site. Evaluation of the site includes defining the relationship between climate variability, as the input function or driver of site- and regional-scale ground-water flow, and the possible transport and release of radionuclides. Secondary calcite and opal have been deposited in the UZ by meteoric waters that infiltrated through overlying soils and percolated through the tuffs. The oxygen isotopic composition ({delta}{sup 18}O values) of these minerals reflect contemporaneous meteoric waters and the {delta}{sup 13}C values reflect soil organic matter, and hence the resident plant community, at the time of infiltration (Whelan et al., 1994). Recent U/Pb age determinations of opal in these occurrences allows the {delta}{sup 13}C values of associated calcite to be used to reconstruct general climate variations during the past 9 M.y.

  4. Calibration of Yucca Mountain unsaturated zone flow and transport model using porewater chloride data.

    PubMed

    Liu, Jianchun; Sonnenthal, Eric L; Bodvarsson, Gudmundur S

    2003-01-01

    In this study, porewater chloride data from Yucca Mountain, NV are analyzed and modeled by three-dimensional chemical transport simulation and analytical methods. The simulation modeling approach is based on a continuum formulation of coupled multiphase fluid flow and tracer transport processes through fractured porous rock using a dual-continuum concept. Infiltration rate calibrations were performed using the porewater chloride data. Model results of chloride distributions were improved in matching the observed data with the calibrated infiltration rates. Statistical analyses of the frequency distribution for overall percolation fluxes and chloride concentration in the unsaturated zone system demonstrate that the use of the calibrated infiltration rates had an insignificant effect on the distribution of simulated percolation fluxes but significantly changed the predicted distribution of simulated chloride concentrations. An analytical method was also applied to model transient chloride transport. The method was verified by three-dimensional simulation results to be capable of capturing major chemical transient behavior and trends. Effects of lateral flow in the Paintbrush nonwelded unit on percolation fluxes and chloride distribution were studied by three-dimensional simulations with increased horizontal permeability. The combined results from these model calibrations furnish important information for the UZ model studies, contributing to performance assessment of the potential repository. PMID:12714292

  5. PORE-WATER ISOTOPIC COMPOSITION AND UNSATURATED-ZONE FLOW, YUCCA MOUNTAIN, NEVADA

    SciTech Connect

    C. Yang

    2000-10-23

    Site characterization at Yucca Mountain, Nevada, the site of a potential high-level radioactive waste repository, has included studies of recharge, flow paths, percolation flux, perched water bodies, and chemical compositions of the water in the thick unsaturated zone (UZ). Samples of pore water from cores of two recently drilled boreholes, USW SD-6 near the ridge top of Yucca Mountain and USW WT-24 north of Yucca mountain, were analyzed for isotopic compositions as part of a study by the US Geological Survey (USGS), in cooperation with the US Department of Energy, under Interagency Agreement DE-AI08-97NV12033. The purpose of this report is to interpret {sup 14}C, {delta}{sup 13}C, {sup 3}H, {delta}D and {delta}{sup 18}O isotopic compositions of pore water from the core of boreholes USW SD-6 and USW WT-24 in relation to sources of recharge and flow paths in the UZ at Yucca Mountain. Borehole designation USW SD-6 and USW WT-24 subsequently will be referred to as SD-6 and WT-24. The sources of recharge and flow paths are important parameters that can be used in a UZ flow model, total system performance assessment (TSPA), and the license application (LA) for the potential repository at Yucca Mountain.

  6. Three-Dimensional Radionuclide Transport Through the Unsaturated Zone of the Yucca Mountain Site 3 Colloids

    SciTech Connect

    G. J. Moridis; Y. Seol

    2007-01-26

    The authors investigated colloid transport in the unsaturated fractured zone by means of three-dimensional site-scale numerical model under present-day climate infiltration, considering varying colloid diameters, kinetic declogging, and filtration. The radionuclide transport model was used to simulate continuous release of colloids into fractures throughout the proposed repository, in which any components of engineered barrier system such as waste package or drip shield were not considered. the results of the study indicate the importance of subsurface geology and site hydrology, i.e., the presence of faults (they dominate and control transport), fractures (the main migration pathways), and the relative distribution of zeolitic and vitric tuffs. The simulations indicate that (1) colloid transport is not significantly affected by varying the filtration parameters, (2) travel time to the water table decreases with the colloid size, (3) larger colloids show little retardation whereas very small ones are retarded significantly, and (4) fracture filtration can have an impact on transport. Because of uncertainties in the fundamentals of colloid transport and an extremely conservative approach (based on an improbably adverse worst-case scenario), caution should be exercised in the analysis and interpretation of the 3-D simulation results. The results discussed here should be viewed as an attempt to identify and evaluate the mechanisms, processes, and geological features that control colloidal transport.

  7. Calibration of Yucca Mountain unsaturated zone flow and transport model using porewater chloride data

    SciTech Connect

    Liu, Jianchun; Sonnenthal, Eric L.; Bodvarsson, Gudmundur S.

    2002-09-01

    In this study, porewater chloride data from Yucca Mountain, Nevada, are analyzed and modeled by 3-D chemical transport simulations and analytical methods. The simulation modeling approach is based on a continuum formulation of coupled multiphase fluid flow and tracer transport processes through fractured porous rock, using a dual-continuum concept. Infiltration-rate calibrations were using the pore water chloride data. Model results of chloride distributions were improved in matching the observed data with the calibrated infiltration rates. Statistical analyses of the frequency distribution for overall percolation fluxes and chloride concentration in the unsaturated zone system demonstrate that the use of the calibrated infiltration rates had insignificant effect on the distribution of simulated percolation fluxes but significantly changed the predicated distribution of simulated chloride concentrations. An analytical method was also applied to model transient chloride transport. The method was verified by 3-D simulation results as able to capture major chemical transient behavior and trends. Effects of lateral flow in the Paintbrush nonwelded unit on percolation fluxes and chloride distribution were studied by 3-D simulations with increased horizontal permeability. The combined results from these model calibrations furnish important information for the UZ model studies, contributing to performance assessment of the potential repository.

  8. Advective Desorption of Uranium (VI) from Contaminated Hanford Vadose Zone Sediments under Saturated and Unsaturated Conditions

    SciTech Connect

    Wellman, Dawn M.; Zachara, John M.; Liu, Chongxuan; Qafoku, Nikolla; Smith, Steven C.; Forrester, Steven W.

    2008-11-03

    Sedimentary, hydrologic, and geochemical variations in the Hanford subsurface environment, as well as compositional differences in contaminating waste streams, have created vast differences in the migration and mobility of uranium within the subsurface environment. A series of hydraulically-saturated and -unsaturated column experiments were performed to i.) assess the effect of water content on the advective desorption and migration of uranium from contaminated sediments, and ii.) evaluate the uranium concentration that can develop in porewater and/or groundwater as a result of desorption/dissolution reactions. Flow rate and moisture content were varied to evaluate the influence of contact time, pore water velocity, and macropore desaturation on aqueous uranium concentrations. Sediments were collected from the T-TX-TY tank farm complex and the 300 Area Process Ponds located on the Hanford Site, southeastern Washington State. The sediments vary in depth, mineralogy, and in contamination events. Experiments were conducted under mildly alkaline/calcareous conditions representative of conditions commonly encountered at repository sites across the arid western United States and, in particular, the Hanford site. Results illustrate the release of uranium from these sediments is kinetically controlled and low water contents encountered within the Hanford vadose zone result in the formation of mobile-immobile water regimes, which isolate a fraction of the reactive sites within the sediments, effectively reducing the concentration of uranium released into migrating porewaters.

  9. Distribution of fast hydrologic paths in the unsaturated zone at Yucca Mountain

    SciTech Connect

    Fabryka-Martin, J.T.; Wolfsberg, A.V.; Levy, S.S.; Roach, J.L.; Winters, S.T.; Wolfsberg, L.E.; Elmore, D.; Sharma, P.

    1998-12-31

    Development and testing of conceptual flow and transport models for hydrologic systems are strengthened when natural environmental tracers are incorporated into the process. One such tracer is chlorine-36 ({sup 36}Cl, half-life, 301,000 years), a radioactive isotope produced in the atmosphere and carried underground with percolating groundwater. High concentrations of this isotope were also added to meteoric water during a period of global fallout from atmospheric testing of nuclear devices, primarily in the 1950s. This bomb-pulse signal has been used to test for the presence of fast transport paths in the unsaturated zone at Yucca Mountain and to provide the basis for a conceptual model for their distribution. Yucca Mountain is under investigation by the US Department of Energy as a potential site at which to host an underground high-level radioactive waste repository. Under wetter climatic conditions, fast-flow pathways will respond quickly to increases in infiltration and have the potential to become seeps in the tunnel drifts. The {sup 36}Cl data are also being used in numerical flow and transport models to establish lower bounds on infiltration rates, estimate ground water ages, and establish bounding values for hydrologic flow parameters governing fracture transport.

  10. Evidence for an unsaturated-zone origin of secondary minerals in Yucca Mountain, Nevada

    SciTech Connect

    Whelan, Joseph F.; Roedder, Edwin; Paces, James B.

    2001-04-29

    The unsaturated zone (UZ) in Miocene-age welded tuffs at Yucca Mountain, Nevada, is under consideration as a potential site for the construction of a high-level radioactive waste repository. Secondary calcite and silica minerals deposited on fractures and in cavities in the UZ tuffs are texturally, isotopically, and geochemically consistent with UZ deposition from meteoric water infiltrating at the surface and percolating through the UZ along fractures. Nonetheless, two-phase fluid inclusions with small and consistent vapor to liquid (V:L) ratios that yield consistent temperatures within samples and which range from about 35 to about 80 C between samples have led some to attribute these deposits to formation from upwelling hydrothermal waters. Geochronologic studies have shown that calcite and silica minerals began forming at least 10 Ma and continued to form into the Holocene. If their deposition were really from upwelling water flooding the UZ, it would draw into question the suitability of the site as a waste repository.

  11. Water flow modeling in the unsaturated zone with imprecise parameters using a fuzzy approach

    NASA Astrophysics Data System (ADS)

    Schulz, K.; Huwe, B.

    1997-12-01

    An alternative approach, based on fuzzy set theory, is presented to express imprecision of parameters in a non-probabilistic sense. Imprecision may originate from indirect measurements, estimation routines, subjective interpretation and expert judgement of available information. One dimensional, steady state water flow in the unsaturated zone of homogeneous soils, which is described by the Darcy-Buckingham equation, was chosen to evaluate and to incorporate fuzzy soil hydraulic properties and boundary conditions in the modeling procedure. It is here used to describe soil water pressures with depth, as well as to calculate maximum evapotranspiration rates under steady state conditions. Solving the fuzzy equation for steady state water flow results in minimizing/maximizing procedures, from where resulting membership functions of the dependent variable are calculated. A comparison to a more classical stochastic approach points out the main differences between fuzzy and stochastic concepts to account for uncertainties. Finally, a sensitivity analysis shows the strong impact of different shapes of membership functions of the input parameters on the resulting membership functions of maximum evapotranspiration rates and soil water pressures.

  12. Movement of moisture in the unsaturated zone in a loess-mantled area, southwestern Kansas

    USGS Publications Warehouse

    Prill, Robert C.

    1977-01-01

    A study of moisture movement associated with ponding near Garden City, Kansas, indicates that loess-manted areas have excellent potential for artificial recharge by water spreading. Infiltration stabilized at rates ranging from 0.7 to 2.2 feet (0.2 to 0.7 meter) per day reflecting changes in hydraulic conductivity of soil horizons. Results of the study indicate that the underlying loess has the capacity to temporarily store about 1 cubic foot (0.03 cubic meter) of water for each 6 cubic feet (0.17 cubic meter) of material. Owing to relatively high hydraulic conductivities of the loess and alluvium, however, moisture continues to move through the unsaturated zone. After application of 21 feet (6 meters) of water, mounding at the water table had a maximum thickness of 2 feet (0.6 meter) at the edge of the pond. Although the boundary of mounding spread rapidly, the applied water moved slowly by lateral displacement. (Woodard-USGS)

  13. Percolation and particle transport in the unsaturated zone of a karst aquifer.

    PubMed

    Pronk, Michiel; Goldscheider, Nico; Zopfi, Jakob; Zwahlen, Francxois

    2009-01-01

    Recharge and contamination of karst aquifers often occur via the unsaturated zone, but the functioning of this zone has not yet been fully understood. Therefore, irrigation and tracer experiments, along with monitoring of rainfall events, were used to examine water percolation and the transport of solutes, particles, and fecal bacteria between the land surface and a water outlet into a shallow cave. Monitored parameters included discharge, electrical conductivity, temperature, organic carbon, turbidity, particle-size distribution (PSD), fecal indicator bacteria, chloride, bromide, and uranine. Percolation following rainfall or irrigation can be subdivided into a lag phase (no response at the outlet), a piston-flow phase (release of epikarst storage water by pressure transfer), and a mixed-flow phase (increasing contribution of freshly infiltrated water), starting between 20 min and a few hours after the start of recharge event. Concerning particle and bacteria transport, results demonstrate that (1) a first turbidity signal occurs during increasing discharge due to remobilization of particles from fractures (pulse-through turbidity); (2) a second turbidity signal is caused by direct particle transfer from the soil (flow-through turbidity), often accompanied by high levels of fecal indicator bacteria, up to 17,000 Escherichia coli/100 mL; and (3) PSD allows differentiation between the two types of turbidity. A relative increase of fine particles (0.9 to 1.5 microm) coincides with microbial contamination. These findings help quantify water storage and percolation in the epikarst and better understand contaminant transport and attenuation. The use of PSD as "early-warning parameter" for microbial contamination in karst water is confirmed. PMID:19462487

  14. Hydrogeology of the unsaturated zone, North Ramp area of the Exploratory Studies Facility, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Rousseau, Joseph P., (Edited By); Kwicklis, Edward M.; Gillies, Daniel C.

    1999-01-01

    Yucca Mountain, in southern Nevada, is being investigated by the U.S. Department of Energy as a potential site for a repository for high-level radioactive waste. This report documents the results of surface-based geologic, pneumatic, hydrologic, and geochemical studies conducted during 1992 to 1996 by the U.S. Geological Survey in the vicinity of the North Ramp of the Exploratory Studies Facility (ESF) that are pertinent to understanding multiphase fluid flow within the deep unsaturated zone. Detailed stratigraphic and structural characteristics of the study area provided the hydrogeologic framework for these investigations. Multiple lines of evidence indicate that gas flow and liquid flow within the welded tuffs of the unsaturated zone occur primarily through fractures. Fracture densities are highest in the Tiva Canyon welded (TCw) and Topopah Spring welded (TSw) hydrogeologic units. Although fracture density is much lower in the intervening nonwelded and bedded tuffs of the Paintbrush nonwelded hydrogeologic unit (PTn), pneumatic and aqueous-phase isotopic evidence indicates that substantial secondary permeability is present locally in the PTn, especially in the vicinity of faults. Borehole air-injection tests indicate that bulk air-permeability ranges from 3.5x10-14 to 5.4x10-11 square meters for the welded tuffs and from 1.2x10-13 to 3.0x10-12 square meters for the non welded and bedded tuffs of the PTn. Analyses of in-situ pneumatic-pressure data from monitored boreholes produced estimates of bulk permeability that were comparable to those determined from the air-injection tests. In many cases, both sets of estimates are two to three orders of magnitude larger than estimates based on laboratory analyses of unfractured core samples. The in-situ pneumatic-pressure records also indicate that the unsaturated-zone pneumatic system consists of four subsystems that coincide with the four major hydrogeologic units of the unsaturated zone at Yucca Mountain. In

  15. Pore-Water Extraction from Unsaturated Porous Media: Intermediate-Scale Laboratory

    SciTech Connect

    Oostrom, Martinus; Truex, Michael J.; Wietsma, Thomas W.; Tartakovsky, Guzel D.

    2014-08-15

    As a remedial approach, vacuum-induced pore-water extraction offers the possibility of contaminant and water removal from the vadose zone, which may be beneficial in reducing the flux of vadose zone contaminants to groundwater. Vadose zone water extraction is being considered at the Hanford Site in Washington State as a means to remove technetium-99 contamination from low permeability sediments with relatively high water contents. A series of intermediate-scale laboratory experiments have been conducted to improve the fundamental understanding and limitations of the technique. Column experiments were designed to investigate the relations between imposed suctions, water saturations, and water production. Flow cell experiments were conducted to investigate the effects of high-permeability layers and near-well compaction on pore-water extraction efficiency. Results show that water extraction from unsaturated systems can be achieved in low permeability sediments, provided that the initial water saturations are relatively high. The presence of a high-permeability layer decreased the yield, and compaction near the well screen had a limited effect on overall performance. In all experiments, large pressure gradients were observed near the extraction screen. Minimum requirements for water extraction include an imposed vacuum-induced suction larger than the initial sediment capillary pressure, in combination with a fully saturated seepage-face boundary. A numerical multiphase simulator with a coupled seepage-face boundary conditions was used to simulate the experiments. Reasonable matches were obtained between measured and simulated results for both water extraction and capillary pressures, suggesting that numerical simulations may be used as a design tool for field-scale applications of pore-water extraction.

  16. Direct current resistivity profiling to study distribution of water in the unsaturated zone near the Amargosa Desert Research Site, Nevada

    USGS Publications Warehouse

    Abraham, Jared D.; Lucius, Jeffrey E.

    2004-01-01

    In order to study the distribution of water in the unsaturated zone and potential for ground-water recharge near the Amargosa Desert Research Site south of Beatty, Nevada, the U.S. Geological Survey collected direct-current resistivity measurements along three profiles in May 2003 using an eight-channel resistivity imaging system. Resistivity data were collected along profiles across the ADRS, across a poorly incised (distributary) channel system of the Amargosa River southwest of the ADRS, and across a well-incised flood plain of the Amargosa River northwest of the ADRS. This report describes results of an initial investigation to estimate the distribution of water in the unsaturated zone and to evaluate the shallow subsurface stratigraphy near the ADRS. The geophysical method of dc resistivity was employed by using automated data collection with numerous electrodes. 'Cross sections' of resistivity, produced by using an inversion algorithm on the field data, at the three field sites are presented and interpreted.

  17. Residence time, mineralization processes and groundwater origin within a carbonate coastal aquifer with a thick unsaturated zone

    NASA Astrophysics Data System (ADS)

    Santoni, S.; Huneau, F.; Garel, E.; Vergnaud-Ayraud, V.; Labasque, T.; Aquilina, L.; Jaunat, J.; Celle-Jeanton, H.

    2016-09-01

    This study aims at establishing groundwater residence times, identifying mineralization processes and determining groundwater origins within a carbonate coastal aquifer with thick unsaturated zone and lying on a granitic depression. A multi-tracer approach (major ions, SiO2, Br-, Ba+, Sr2+, 18O, 2H, 13C, 3H, Ne, Ar) combined with a groundwater residence time determination using CFCs and SF6 allows defining the global setting of the study site. A typical mineralization conditioned by the sea sprays and the carbonate matrix helped to validate the groundwater weighted residence times from using a binary mixing model. Terrigenic SF6 excesses have been detected and quantified, which permits to identify a groundwater flow from the surrounding fractured granites towards the lower aquifer principally. The use of CFCs and SF6 as a first hydrogeological investigation tool is possible and very relevant despite the thick unsaturated zone and the hydraulic connexion with a granitic environment.

  18. Subtsve A~é­ An In-situ Remediation Method For The Saturated and Unsaturated Zone

    NASA Astrophysics Data System (ADS)

    Koschitzky, H.-P.; Troetschler, O.; Weber, K.

    two different industrial sites, the ratio is about 1 until the steam hits the unsaturated zone. The remediation efficiency for a site-specific multi-component contamination in the groundwater fluctuation zone was investigated in 2-D experiments comparing the 1 steam injection into the groundwater with the steam injection into the capillary fringe. A slightly higher effectiveness with a recovery rate of more than 97% was measured for the steam injection into the groundwater. A significant difference between both methods was obtained in the kind of removal of the contaminants. SubTSVE yields to a higher mass removal by phase extraction from the groundwater table as a free organic phase. To reduce the risk of mobilisation as a free product the injection of a steam-air mixture into the groundwater is proposed in order to evaporate the contaminants. The effects of steam-air injection will be investigated in VEGAS large container (l = 6 m, w = 3 m, h = 4.5 m) filled with soil from an industrial site and compared with those of steam injection within the same container. References ITAMURA &UDELL (1993): Experimental Cleanup of a Dense Non-Aqueous Phase Liqid in the Unsaturated Zone of a Porous Medium Using Steam Injection, Multiphase Transport in Porous Media, ASME, HTD-Vol. 265, 57-62 FÄRBER, A. (1997): Wärmetransport in der ungesättigten Bodenzone: Entwicklung einer thermischen In-situ-Sanierungstechnologie, Mitteilungen Institut für Wasserbau, Universität Stuttgart, Heft 96 UDELL et al. (1994): NAS Lemoore JP-5 cleanup demonstration, Berkeley Environ- mental Restoration Center, University of California, Berkeley NEWMARK &AINES (1995): Summary of the LLNL Gasoline Spill Demonstration Dynamic Underground Stripping Project, Lawrence Livermore Natl. Lab., UCRL-ID- 120416 SCHMIDT et al. (1999): Pilothafte Sanierung eines BTEX Schadens an einem ehema- ligen Gaswerksstandort mit der thermisch unterstützten Bodenluftabsaugung (TUBA) durch Dampfinjektion, Wiss. Bericht WB 99

  19. A Reservoir of Natural Perchlorate in Unsaturated Zones of Arid and Semi-Arid Regions, Southwestern USA

    NASA Astrophysics Data System (ADS)

    Rao, B. A.; Stonestrom, D. A.; Anderson, T. A.; Orris, G. J.; Rajagapolan, S.; Sandvig, R. M.; Scanlon, B. R.; Walvoord, M. A.; Jackson, W.

    2006-12-01

    Natural perchlorate (ClO4-) is generally present in unsaturated zones of steppe-to-desert regions of the arid and semi-arid southwestern United States. The perchlorate is associated with atmospherically deposited chloride that has accumulated throughout the Holocene. To assess this natural reservoir, we analyzed unsaturated-zone profiles from ten sites across Nevada, New Mexico, Texas, and Utah for perchlorate and other anions. The sampled sites represent a wide range of precipitation (0.1 0.5 m yr-1), dominant vegetation, soil type, underlying geology, and include five distinct ecological regions: Chihuahuan, Mojave, and southern Great Basin deserts; Arizona-New Mexico semi-desert; and Texas High Plains dry steppe. Concentrations of perchlorate correlated closely with chloride and bromide. The perchlorate reservoir (up to 1 kg ha-1) is sufficiently large to impact groundwater when natural recharge during pluvial periods or induced recharge after conversion to agriculture flushes accumulated salts from the unsaturated zone. This little explored source can explain perchlorate in milk and other agricultural products far from anthropogenic contamination, and should be considered when evaluating overall exposure risk.

  20. Effects of carbon dioxide variations in the unsaturated zone on water chemistry in a glacial-outwash aquifer

    USGS Publications Warehouse

    Lee, R.W.

    1997-01-01

    The research site at Otis Air Base, Cape Cod, Massachusetts, has been developed for hydrogeological and geochemical studies of sewage-effluent contaminated groundwater since 1982. Research of hydrologic properties, transport, and chemical and biological processes is ongoing, but the origin of background water chemistry has not been determined. The principal geochemical process giving rise to the observed background water chemistry is CO2-controlled hydrolysis of Na feldspar. Geochemical modeling demonstrated that CO2 sources could vary over the project area. Analyses of unsaturated zone gases showed variations in CO2 which were dependent on land use and vegetative cover in the area of groundwater recharge. Measurements of CO2 in unsaturated-zone gases showed that concentrations of total inorganic C in recharge water should range from about 0.035 to 1.0 mmoles/L in the vicinity of Otis Air Base. Flux of CO2 from the unsaturated zone varied for a principal land uses, ranging from 86 gC/m2/yr for low vegetated areas to 1630 gC/m2/yr for a golf course. Carbon dioxide flux from woodlands was 220 gC/m2/yr, lower than reported fluxes of 500 to 600 gC/m2/yr for woodlands in a similar climate. Carbon dioxide flux from grassy areas was 540 gC/m2/yr, higher than reported fluxes of 230 to 490 gC/m2/yr for grasslands in a similar climate.

  1. Uncertainty quantification for unsaturated flow in porous media: a stochastic collocation method

    NASA Astrophysics Data System (ADS)

    Barajas-Solano, D. A.; Tartakovsky, D. M.

    2011-12-01

    We present a stochastic collocation (SC) method to quantify epistemic uncertainty in predictions of unsaturated flow in porous media. SC provides a non-intrusive framework for uncertainty propagation in models based on the non-linear Richards' equation with arbitrary constitutive laws describing soil properties (relative conductivity and retention curve). To illustrate the approach, we use the Richards' equation with the van Genutchen-Mualem model for water retention and relative conductivity to describe infiltration into an initially dry soil whose uncertain parameters are treated as random fields. These parameters are represented using a truncated Karhunen-Loève expansion; Smolyak algorithm is used to construct a structured set of collocation points from univariate Gauss quadrature rules. A resulting deterministic problem is solved for each collocation point, and together with the collocation weights, the statistics of hydraulic head and infiltration rate are computed. The results are in agreement with Monte Carlo simulations. We demonstrate that highly heterogeneous soils (large variances of hydraulic parameters) require cubature formulas of high degree of exactness, while their short correlation lengths increase the dimensionality of the problem. Both effects increase the number of collocation points and thus of deterministic problems to solve, affecting the overall computational cost of uncertainty quantification.

  2. The Apparent Conductivity for Steady Unsaturated Flow in Periodically Fractured Porous Media

    NASA Astrophysics Data System (ADS)

    Martinez, M. J.; Dykhuizen, R. C.; Eaton, R. R.

    1992-11-01

    The influence of horizontal fractures on the steady seepage of moisture in variably saturated porous media is analyzed by analytical and numerical means. The fractures are assumed to contain many open (dry) regions, and to be distributed periodically in two dimensions. The dry regions of the fracture form a barrier to moisture flow through the geologic medium. An idealized two-dimensional model that maximizes the barrier effect of the fractures is analyzed. The results of the analysis quantify the effect of the dry regions of the fractures on global water flow through the fractured medium. An apparent conductivity is determined such that the fractured system can be replaced by a homogeneous medium for describing steady unsaturated flow. An asymptotic analysis yields an analytic expression for the apparent hydraulic conductivity through such a system in the limit of small sorptive number (fracture spacing divided by a characteristic capillary suction) for the intact matrix material. The apparent hydraulic conductivity for arbitrary spacing and sorptive number is determined by numerical means. The numerical model accounts for variable hydraulic conductivity as a function of the local pressure head, whereas the asymptotic solution represents the limit of constant conductivity. The numerical results confirm the analytical solution as a lower bound on the apparent hydraulic conductivity.

  3. FEMWATER: a finite-element model of water flow through saturated-unsaturated porous media

    SciTech Connect

    Yeh, G.T.; Ward, D.S.

    1980-10-01

    Upon examining the Water Movement Through Saturated-Unsaturated Porous Media: A Finite-Element Galerkin Model, it was felt that the model should be modified and expanded. The modification is made in calculating the flow field in a manner consistent with the finite element approach, in evaluating the moisture-content increasing rate within the region of interest, and in numerically computing the nonlinear terms. With these modifications, the flow field is continuous everywhere in the flow regime, including element boundaries and nodal points, and the mass loss through boundaries is much reduced. Expansion is made to include four additional numerical schemes which would be more appropriate for many situations. Also, to save computer storage, all arrays pertaining to the boundary condition information are compressed to smaller dimension, and to ease the treatment of different problems, all arrays are variably dimensioned in all subroutines. This report is intended to document these efforts. In addition, in the derivation of finite-element equations, matrix component representation is used, which is believed more readable than the matrix representation in its entirety. Two identical sample problems are simulated to show the difference between the original and revised models.

  4. Tritium plume dynamics in the shallow unsaturated zone in an arid environment

    USGS Publications Warehouse

    Maples, S.R.; Andraski, B.J.; Stonestrom, D.A.; Cooper, C.A.; Pohll, G.; Michel, R.L.

    2014-01-01

    The spatiotemporal variability of a tritium plume in the shallow unsaturated zone and the mechanisms controlling its transport were evaluated during a 10-yr study. Plume movement was minimal and its mass declined by 68%. Upward-directed diffusive-vapor tritium fluxes and radioactive decay accounted for most of the observed plume-mass declines. Effective isolation of tritium (3H) and other contaminants at waste-burial facilities requires improved understanding of transport processes and pathways. Previous studies documented an anomalously widespread (i.e., theoretically unexpected) distribution of 3H (>400 m from burial trenches) in a dry, sub-root-zone gravelly layer (1–2-m depth) adjacent to a low-level radioactive waste (LLRW) burial facility in the Amargosa Desert, Nevada, that closed in 1992. The objectives of this study were to: (i) characterize long-term, spatiotemporal variability of 3H plumes; and (ii) quantify the processes controlling 3H behavior in the sub-root-zone gravelly layer beneath native vegetation adjacent to the facility. Geostatistical methods, spatial moment analyses, and mass flux calculations were applied to a spatiotemporally comprehensive, 10-yr data set (2001–2011). Results showed minimal bulk-plume advancement during the study period and limited Fickian spreading of mass. Observed spreading rates were generally consistent with theoretical vapor-phase dispersion. The plume mass diminished more rapidly than would be expected from radioactive decay alone, indicating net efflux from the plume. Estimates of upward 3H efflux via diffusive-vapor movement were >10× greater than by dispersive-vapor or total-liquid movement. Total vertical fluxes were >20× greater than lateral diffusive-vapor fluxes, highlighting the importance of upward migration toward the land surface. Mass-balance calculations showed that radioactive decay and upward diffusive-vapor fluxes contributed the majority of plume loss. Results indicate that plume losses

  5. High mobility of SDBS-dispersed single-walled carbon nanotubes in saturated and unsaturated porous media.

    PubMed

    Tian, Yuan; Gao, Bin; Ziegler, Kirk J

    2011-02-28

    Knowledge of the mobility of carbon nanotubes (CNTs) in porous media is very important to assess their impacts on the environment. In this study, a series of laboratory experiments were conducted to explore the transport mechanisms of sonication shortened, sodium dodecylbenzene sulfonate (SDBS) dispersed single-walled nanotubes (SWNTs) in both saturated and unsaturated sand columns. Laboratory columns packed with quartz sand with different combinations of moisture content and grain-size distribution were used to examine the breakthrough behavior of the SDBS-dispersed SWNTs. Bubble column experiments were also conducted to study the interactions between the SDBS-dispersed SWNTs and the air-water interface. Packed-column experimental results showed that the SDBS-dispersed SWNTs were highly mobile for most of the experimental conditions tested. The surface deposition of the SWNTs in the sand columns was low because all the interactive surfaces were negatively charged. Physical trapping was not observed for the SWNTs in the saturated porous media of different grain-size distributions because the SWNTs might orient parallel to the streamlines in flow to reduce their retention. Retention of the SWNTs in unsaturated porous media occurred only at a very low moisture content (<0.10). Otherwise, reduction in moisture content showed little impact on the retention and transport of the SWNTs in unsaturated porous media. Findings from the bubble-column experiments confirmed that the SDBS-dispersed SWNTs did not attach to the air-water interface. A mathematical model based on the advection-dispersion equation coupled with reaction-rate laws successfully described the retention and transport of the SDBS-dispersed SWNTs in both water-saturated and unsaturated columns. PMID:21236566

  6. Experimental Investigation of the Effective Foam Viscosity in Unsaturated Porous Media

    SciTech Connect

    Zhang, Z. F.; Zhong, Lirong; White, Mark D.; Szecsody, James E.

    2012-11-01

    Foam has the potential to effectively carry and distribute either aqueous or gaseous amendments to the deep vadose zone for contaminant remediation. However, the transport of foam in porous media is complicated because flow characteristics such as the effective viscosity are affected not only by foam properties but also by the sediment properties and flow conditions. We determined the average effective foam viscosity via a series of laboratory experiments and found that the effective foam viscosity increased with the liquid fraction in foam, the injection rate, and sediment permeability. These impacts are quantified with an empirical expression, which is further demonstrated with data from literature. The results show that the liquid fraction in foam and sediment permeability are two primary factors affecting effective foam viscosity. These results suggest that, when foam is used in deep vadose zone remediation, foam flow will not suffer from gravitational drainage and can distribute amendments uniformly in heterogeneous sediments.

  7. Effects of precipitation patterns on catchment erosion considering unsaturated zone hydrology

    NASA Astrophysics Data System (ADS)

    Norouzi Moghanjoghi, Karim; Ehlers, Todd A.

    2015-04-01

    Geomorphological models are based on simplifying hydrological assumptions due to the computational limitations. The runoff generation method used in these models is generally the Hortonian excess rainfall. This assumption does not take into account the response of unsaturated zone to the dry intervals and precipitation event's duration and looks only at the intensity of the precipitation events. It also implies that the smaller intensity precipitations does not incise or erode the river. This study compliments previous work by investigating the 3D transient response of the unsaturated zone, river flow and erosion power to different precipitation patterns of fixed total precipitation. The catchment of interest is 150km2 with a relief of 900m located in the south of Germany. The total amount of surface shear from runoff is computed as a measure of effectiveness of the incision and bedrock erosion. The sensitivity of the erosion on the surface is calculated with sampling multiple precipitations of the varying intensity, duration and dry intervals using using a 3D transient hydrologic model called Hydrogeosphere. Three types of experiments are designed where in each experiment, one precipitation characteristic (i.e. duration) is kept constant and the other two precipitation parameters are allowed to vary (i.e. intensity and dry intervals). The number of events are varied, but produce a fixed total precipitation amount of 700 mm over six months. An exponential probability distribution for the intensity, duration and dry intervals was explored in 300 simulations. These precipitation events are simulated and the shear stress over the stream is sampled every half hour. Model results show that the combined effects of intensity, duration and dry intervals on shear stress over the river is significant even with the total fixed precipitation. Experiment I consists of events with small mean intensities and long durations. These events are less effective in eroding the channel

  8. Archaeology and public perception of a trans-scientific problem; disposal of toxic wastes in the unsaturated zone

    USGS Publications Warehouse

    Winograd, Isaac Judah

    1986-01-01

    Predicting the effects of toxic-waste disposal on the environment over periods of millenia to hundreds of millenia is a transscientific problem; that is, one not fully addressed by quantitative scientific and engineering endeavors. Archaeology is a pertinent adjunct to such predictions in several ways. First, and foremost, archaeological records demonstrate that delicate, as well as durable, objects buried in thick unsaturated zones of arid and semiarid environments may survive intact for millenia to tens of millenia. This successful preservation of Late Paleolithic to Iron Age artifacts provides independent support for the tentative favorable conclusions of earth scientists regarding the general utility of thick unsaturated zones for toxic-waste isolation. By analogy with the archaeological record, solidified toxic wastes of low solubility that are buried in arid unsaturated zones should remain isolated from the environment indefinitely; modern man presumably should be able to improve upon the techniques used by his ancestors to isolate and preserve their sacred and utilitarian objects. Second, archaeological evidence pertinent to the fate of objects buried in unsaturated zones-although qualitative in nature and subject to the limitations of arguments by analogy-is meaningful to the public and to the courts who, with some scientists and engineers, are reluctant to rely exclusively on computer-generated predictions of the effects of buried toxic wastes on the environment. Third, the archaeological record issues a warning that our descendants may intrude into our waste disposal sites and that we must therefore take special measures to minimize such entry and, if it occurs, to warn of the dangers by a variety of symbols. And fourth, archaeology provides a record of durable natural and manmade materials that may prove to be suitable for encapsulation of our wastes and from which we can construct warning markers that will last for millenia. For these four reasons

  9. Herbicide Transport and Transformations in the Unsaturated Zone of Three Small Agricultural Basins with Corn and Soybean Row Crops

    NASA Astrophysics Data System (ADS)

    Hancock, T. C.; Vogel, J. R.; Sandstrom, M. W.; Capel, P. D.; Bayless, R. E.; Webb, R. M.

    2006-05-01

    In the United States, herbicides are among the most significant nonpoint-source pollutants and were applied to 95% of all fields in corn production and 97% of all fields in soybean production in 2003 and 2004. The United States Geological Survey (USGS) has conducted a study on select herbicides in the unsaturated zone under corn and soybean fields in three predominantly agricultural basins: Morgan Creek (Maryland), Leary Weber Ditch within Sugar Creek (Indiana), and Maple Creek (Nebraska). In 2004, the Morgan Creek and Leary Weber Ditch fields were in soybeans and the Maple Creek fields were in corn. The Maple Creek fields were irrigated, whereas those in Morgan Creek and Leary Weber Ditch were not. Similarities and differences in agricultural management practices, climatic conditions, and natural features, such as soil types and geology, were evaluated as part of the study. In general, the amounts of herbicides entering the unsaturated zone from rain in these basins were minor (1%) compared to amounts commonly applied to the land surface during agricultural practices. Few herbicides were detected on solid core samples from the unsaturated zones of these basins. An exception was found at a Morgan Creek site in an upland recharge area with sandier soils. Here, atrazine concentrations were highest in the near surface solids and decreased with depth. In the unsaturated-zone porewater of the Morgan Creek Basin, parent triazine and acetanilide herbicides were detected and only at the site in the upland recharge area at relatively low concentrations at depths greater than 4 meters, probably because these compounds had not been applied for several years. At the Morgan Creek and Leary Weber Ditch sites, acetanilide metabolites were frequently detected in the unsaturated-zone porewater. In general, the fraction of metolachlor ethane sulfonic acid (ESA) relative to the total mass of parent and metabolites increased with depth overall and at several individual sampling

  10. Modeling a thick unsaturated zone at San Gorgonio Pass, California: lessons learned after five years of artificial recharge

    USGS Publications Warehouse

    Flint, Alan L.; Ellett, Kevin M.; Christensen, Allen H.; Martin, Peter

    2012-01-01

    The information flow among the tasks of framework assessment, numerical modeling, model forecasting and hind casting, and system-performance monitoring is illustrated. Results provide an understanding of artificial recharge in high-altitude desert settings where large vertical distances may separate application ponds from their target aquifers. Approximately 3.8 million cubic meters of surface water was applied to spreading ponds from 2003–2007 to artificially recharge the underlying aquifer through a 200-meter thick unsaturated zone in the San Gorgonio Pass area in southern California. A study was conducted between 1997 and 2003, and a numerical model was developed to help determine the suitability of the site for artificial recharge. Ongoing monitoring results indicated that the existing model needed to be modified and recalibrated to more accurately predict artificial recharge at the site. The objective of this work was to recalibrate the model by using observation of the application rates, the rise and fall of the water level above a perching layer, and the approximate arrival time to the water table during the 5-yr monitoring period following initiation of long-term artificial recharge. Continuous monitoring of soil-matric potential, temperature, and water levels beneath the site indicated that artificial recharge reached the underlying water table between 3.75 and 4.5 yr after the initial application of the recharge water. The model was modified to allow the simulation to more adequately match the perching layer dynamics and the time of arrival at the water table. The instrumentation also showed that the lag time between changes in application of water at the surface and the response at the perching layer decreased from about 4 mo to less than 1 mo due to the wet-up of the unsaturated zone and the increase in relative permeability. The results of this study demonstrate the importance of iteratively monitoring and modeling the unsaturated zone in layered

  11. Mass exchange between mobile fresh water and immobile saline water in the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Gvirtzman, Haim; Paldor, Nathan; Magaritz, Mordeckai; Bachmat, Yehuda

    1988-10-01

    A profile of tritium concentrations measured in the unsaturated zone in loessial sediments in a semiarid area is interpreted in terms of mobile and immobile water domains, according to a nonequilibrium transport model. The mobile domain is represented by percolating freshwater from both rain and irrigation, and the immobile one is represented by isolated fossil saline water pockets. The two domains are connected by partially saturated narrow passages within dispersed clay minerals. The transport of the mobile water is described by convective-dispersive flow and by mass exchange between the two water domains. The relevant equations with the given initial and boundary conditions are solved numerically, and the simulated profile is adjusted to fit the measured one. In this study we concentrate on examination of the mass exchange law between the two domains. It was assumed that matrix characteristics vary in time due to the dispersion of clays at the interface between fresh and saline waters. Accordingly, a time-dependent mass exchange was adopted, which made it possible to obtain an adequate reconstruction of the measured tritium profile. By using a least squares optimization procedure it was found that the best fit between the simulated and measured profiles is attained when the fraction of mobile water is 30%, and the rate of mass exchange decreases from 0.60 to 0.01 year-1 in 26 years. The proposed model implies is that it is the immobile water domain which contains the memory of the "high tritium period" (thermonuclear tests period) of the 1960s.

  12. Balancing practicality and hydrologic realism: a parsimonious approach for simulating rapid groundwater recharge via unsaturated-zone preferential flow

    USGS Publications Warehouse

    Mirus, Benjamin B.; Nimmo, J.R.

    2013-01-01

    The impact of preferential flow on recharge and contaminant transport poses a considerable challenge to water-resources management. Typical hydrologic models require extensive site characterization, but can underestimate fluxes when preferential flow is significant. A recently developed source-responsive model incorporates film-flow theory with conservation of mass to estimate unsaturated-zone preferential fluxes with readily available data. The term source-responsive describes the sensitivity of preferential flow in response to water availability at the source of input. We present the first rigorous tests of a parsimonious formulation for simulating water table fluctuations using two case studies, both in arid regions with thick unsaturated zones of fractured volcanic rock. Diffuse flow theory cannot adequately capture the observed water table responses at both sites; the source-responsive model is a viable alternative. We treat the active area fraction of preferential flow paths as a scaled function of water inputs at the land surface then calibrate the macropore density to fit observed water table rises. Unlike previous applications, we allow the characteristic film-flow velocity to vary, reflecting the lag time between source and deep water table responses. Analysis of model performance and parameter sensitivity for the two case studies underscores the importance of identifying thresholds for initiation of film flow in unsaturated rocks, and suggests that this parsimonious approach is potentially of great practical value.

  13. Distribution of gases in the unsaturated zone at a low-level radioactive-waste disposal site near Sheffield, Illinois

    USGS Publications Warehouse

    Striegl, Robert G.

    1988-01-01

    The unsaturated zone is a medium that provides pneumatic communication for the movement of gases from wastes buried in landfills to the atmosphere, biota, and groundwater. Gases in unsaturated glacial and eolian deposits near a waste-disposal trench at the low-level radioactive-waste disposal site near Sheffield, Bureau County, Illinois, were identified, and the spatial and temporal distributions of the partial pressures of those gases were determined for the period January 1984 through January 1986. Methods for the collection and analyses of the gases are described, as are geologic and hydrologic characteristics of the unsaturated zone that affect gas transport. The identified gases, which are of natural and of waste origin, include nitrogen, oxygen, and argon, carbon dioxide, methane, propane, butane, tritiated water vapor, 14carbon dioxide, and 222 radon. Concentrations of methane and 14carbon dioxide originated at the waste, as shown by partial-pressure gradients of the gases; 14carbon dioxide partial pressures exceeded natural background partial pressures by factors greater than 1 million at some locations. Variations in partial pressures of oxygen and carbon dioxide were seasonal among piezometers because of increased root and soil-microbe respiration during summer. Variations in methane and 14carbon dioxide partial pressures were apparently related to discrete releases from waste sources at unpredictable intervals of time. No greater than background partial pressures for tritiated water vapor or 222 radon were measured. (USGS)

  14. Geohydrology, water quality, and nitrogen geochemistry in the saturated and unsaturated zones beneath various land uses, Riverside and San Bernardino counties, California, 1991-93

    USGS Publications Warehouse

    Rees, Terry F.; Bright, D.J.; Fay, R.G.; Christensen, A.H.; Anders, R.B.; Baharie, B.S.; Land, M.T.

    1995-01-01

    The U.S. Geological Survey, in cooperation with the Eastern Municipal Water District, the Metropolitan Water District of Southern California, and the Orange County Water District, has completed a derailed study of the Hemet groundwater basin. The quantity of ground water stored in the basin in August 1992 is estimated to be 327,000 acre-feet. Dissolved-solids concentration ranged from 380 to 700 mg/L (milligrams per liter), except in small areas where the concentration exceeded 1,000 mg/L. Nitrate concentrations exc__*'ded the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) of 10 mg/L nitrate (its nitrogen) in the southeastern part of the basin, in the Domenigoni Valley area, and beneath a dairy in the Diamond Valley area. Seven sites representing selected land uses-residential, tuff grass irrigated with reclaimed water, citrus grove, irrigated farm, poultry farm, and dairy (two sites)--were selected for detailed study of nitrogen geochemistry in the unsaturated zone. For all land uses, nitrate was the dominant nitrogen species in the unsaturated zone. Although nitrate was seasonally present in the shallow unsaturated zone beneath the residential site, it was absent at moderate depths, suggesting negligible migration of nitrate from the surface at this time. Microbial denitrification probably is occurring in the shallow unsaturated zone. High nitrate concentrations in the deep unsaturated zone (greater than 100 ft) suggest either significantly higher nitrate loading at some time in the past, or lateral movement of nitrate at depth. Nitrate also is seasonally present in the shallow unsaturated zone beneath the reclaimed-water site, and (in contrast with the residential site), nitrate is perennially present in the deeper unsaturated zone. Mictobial identification in the unsaturated zone and in the capillary fringe above the water table decreases, the concentrations of nitrate in pore water to below the MCL before reaching the water table. Pore

  15. Unsaturated zone characterization in soil through transient wetting and drying using GPR joint time-frequency analysis and grayscale images

    NASA Astrophysics Data System (ADS)

    Lai, W. L.; Kou, S. C.; Poon, C. S.

    2012-07-01

    SummaryThis paper describes an experimental method to characterize the soil's unsaturated zone by constructing a scenario in which transient downward water infiltration took place from the topsoil to the bottom soil continuously. During the water infiltration, GPR waveforms and side-view grayscale images of the soil column were simultaneously and continuously captured. The GPR wavelets associated with the wetting front were analyzed using short time fourier transform (STFT) algorithm. The downward wetting front and the stretch of unsaturated transition zone decelerated and eased the wetting front's reflection in the time domain; as well as reduced the peak frequency and attenuated the frequency spectra in the frequency domain. The subsequent drying process further attenuated but accelerated the wetting front's reflection in both time and frequency domains. These observations were correlated with the image pixel profiles, from which GPR velocity profiles at different lapsed times were generated after computation via a complex refractive index model (CRIM). The CRIM method is entirely non-invasive and not only offers very detailed measurement of the water saturation profile of the transition zone in laboratory scale, but also is potentially useful for the further study of a variety of vadose zone properties.

  16. Use of borehole neutron logs to estimate moisture content in the unsaturated zone of an alluvial aquifer

    USGS Publications Warehouse

    Quinones-Aponte, Vicente; Carrasquillo, Ramon A.

    1986-01-01

    he neutron borehole logging tool was calibrated for the determination of moisture content in theunsaturated zone of an alluvial aquifer. A continuous core sample was collected to a depth of 15 ft from the unsaturated zone.Moisture content and other soil properties were determined by standard soil-laboratory techniques. The neutron logs profile was correlated to moisture content. The first correlation included all the data points within the unsaturated zone. A correlation coefficient of 0.72 was obtained. An inspection of the plotted data showed that points at the upper extreme of the fitted line departed significantly. A second correlation was tried eliminating data points 1, 3, and 5 which fell too low in the first trial. An almost perfect correlation coefficient of 0.99 was obtained for the data points that were included in the second trial. The criteria used to select the data points for the second correlation trial was that all these points also fell on the left most limit of the neutronprofile. The neutron logs profile, which is like a type of harmonic curve seems to be affected by an undefined factor. Analyzing the shape of the neutron profile it is inferred that hysteresis is the most probable phenomena that is affecting this moisture content profile. Although correlating neutron logs to moisture content is not a straight forward procedure, with an appropriate analysis, calibrated neutron logging tools can be used to determine the moisture content within the unsaturated zone of aquifers. Moisture content should be determined for calibration purposes at least at every foot of depth. Measurements of other elements or factors which may produce the harmonic curve effect might be included in further studies. 

  17. Near Surface Poroelastic Perturbations of Unsaturated Zone Properties of Reservoirs by Distant Earthquakes: Preliminary Results in the Karst System of the LSBB Underground Laboratory

    NASA Astrophysics Data System (ADS)

    Blondel, T.; Emblanch, C.; Gaffet, S.; Guglielmi, Y.; Travi, Y.; Cavaillou, A.; Boyer, D.; Auguste, M.

    2008-12-01

    Earthquakes have been observed to affect the saturated zone of hydrological systems in many different ways -- water wells level changes and variations of springs dischargeand modification of water quality. In comparison very rare researches are conducted on the coupled seismic to rock properties in the shallow unsaturated part of aquifers although the topic is of great concern since this zone is at the interface with the atmosphere and constitutes a major boundary to hydrologic aquifers. A more fundamental concern is to study how a multi-saturated porous rock will respond to seismic loading. The Low-Noise Underground Laboratory of Rustrel-Pays d'Apt (LSBB) offers an easy access to all kinds of unsaturated flows. Indeed, various hydrological responses of macro-fractures and pores were identified and characterized through the combined use of flow and chemical seepage water monitoring. Main results are that some unsaturated flow display permanent flow paths driven by pressure gradients while others remain only driven by gravity. When a distant earthquake occurs, the unsaturated zone dynamic response to seismic waves is systematically monitored both on flow and chemical signals. It results in a complex variation at the permanent well-located seepage points and in eventual outflows at new points. These variations are interpreted as a remobilization of ground-waters stored in the unsaturated zone related to gravity-driven drainage through dilated macro- fractures. Current analyses focus on the estimation of the unsaturated zone hydraulic and mechanical properties variations with time under recurrent distant earthquakes effects.

  18. Evaluating storm-scale groundwater recharge dynamics with coupled weather radar data and unsaturated zone modeling

    NASA Astrophysics Data System (ADS)

    Nasta, P.; Gates, J. B.; Lock, N.; Houston, A. L.

    2013-12-01

    Groundwater recharge rates through the unsaturated zone emerge from complex interactions within the soil-vegetation-atmosphere system that derive from nonlinear relationships amongst atmospheric boundary conditions, plant water use and soil hydraulic properties. While it is widely recognized that hydrologic models must capture soil water dynamics in order to provide reliable recharge estimates, information on episodic recharge generation remains uncommon, and links between storm-scale weather patterns and their influence on recharge is largely unexplored. In this study, the water balance of a heterogeneous one-dimensional soil domain (3 m deep) beneath a typical rainfed corn agro-ecosystem in eastern Nebraska was numerically simulated in HYDRUS-1D for 12 years (2001-2012) on hourly time steps in order to assess the relationships between weather events and episodic recharge generation. WSR-88D weather radar reflectivity data provided both rainfall forcing data (after estimating rain rates using the z/r ratio method) and a means of storm classification on a scale from convective to stratiform using storm boundary characteristics. Individual storm event importance to cumulative recharge generation was assessed through iterative scenario modeling (773 total simulations). Annual cumulative recharge had a mean value of 9.19 cm/yr (about 12 % of cumulative rainfall) with coefficient of variation of 73%. Simulated recharge generation events occurred only in late winter and spring, with a peak in May (about 35% of total annual recharge). Recharge generation is observed primarily in late spring and early summer because of the combination of high residual soil moisture following a winter replenishment period, heavy convective storms, and low to moderate potential evapotranspiration rates. During the growing season, high rates of root water uptake cause rapid soil water depletion, and the concurrent high potential evapotranspiration and low soil moisture prevented recharge

  19. Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes

    NASA Astrophysics Data System (ADS)

    Sprenger, M.; Volkmann, T. H. M.; Blume, T.; Weiler, M.

    2014-10-01

    Determining the soil hydraulic properties is a prerequisite to physically model transient water flow and solute transport in the vadose zone. Estimating these properties by inverse modelling techniques has become more common within the last two decades. While these inverse approaches usually fit simulations to hydrometric data, we expanded the methodology by using independent information about the stable isotope composition of the soil pore water depth profile as a single or additional optimization target. To demonstrate the potential and limits of this approach, we compared the results of three inverse modelling strategies where the fitting targets were (a) pore water isotope concentrations, (b) a combination of pore water isotope concentrations and soil moisture time series, and (c) a two-step approach using first soil moisture data to determine water flow parameters and then the pore water stable isotope concentrations to estimate the solute transport parameters. The analyses were conducted at three study sites with different soil properties and vegetation. The transient unsaturated water flow was simulated by numerically solving the Richards equation with the finite-element code of Hydrus-1D. The transport of deuterium was simulated with the advection-dispersion equation, and the Hydrus code was modified to allow for deuterium loss during evaporation. The Mualem-van Genuchten and the longitudinal dispersivity parameters were determined for two major soil horizons at each site. The results show that approach (a) using only the pore water isotope content cannot substitute hydrometric information to derive parameter sets that reflect the observed soil moisture dynamics, but gives comparable results when the parameter space is constrained by pedotransfer functions. Approaches (b) and (c) using both, the isotope profiles and the soil moisture time series resulted in satisfying model performances and good parameter identifiability. However, approach (b) has the

  20. HYDROBIOGEOCHEM: A coupled model of HYDROlogic transport and mixed BIOGEOCHEMical kinetic/equilibrium reactions in saturated-unsaturated media

    SciTech Connect

    Yeh, G.T.; Salvage, K.M.; Gwo, J.P.; Zachara, J.M.; Szecsody, J.E.

    1998-07-01

    The computer program HYDROBIOGEOCHEM is a coupled model of HYDROlogic transport and BIOGEOCHEMical kinetic and/or equilibrium reactions in saturated/unsaturated media. HYDROBIOGEOCHEM iteratively solves the two-dimensional transport equations and the ordinary differential and algebraic equations of mixed biogeochemical reactions. The transport equations are solved for all aqueous chemical components and kinetically controlled aqueous species. HYDROBIOGEOCHEM is designed for generic application to reactive transport problems affected by both microbiological and geochemical reactions in subsurface media. Input to the program includes the geometry of the system, the spatial distribution of finite elements and nodes, the properties of the media, the potential chemical and microbial reactions, and the initial and boundary conditions. Output includes the spatial distribution of chemical and microbial concentrations as a function of time and space, and the chemical speciation at user-specified nodes.

  1. Vinasse application to sugar cane fields. Effect on the unsaturated zone and groundwater at Valle del Cauca (Colombia).

    PubMed

    Ortegón, Gloria Páez; Arboleda, Fernando Muñoz; Candela, Lucila; Tamoh, Karim; Valdes-Abellan, Javier

    2016-01-01

    Extensive application of vinasse, a subproduct from sugar cane plantations for bioethanol production, is currently taking place as a source of nutrients that forms part of agricultural management in different agroclimatic regions. Liquid vinasse composition is characterised by high variability of organic compounds and major ions, acid pH (4.7), high TDS concentration (117,416-599,400mgL(-1)) and elevated EC (14,350-64,099μScm(-1)). A large-scale sugar cane field application is taking place in Valle del Cauca (Colombia), where monitoring of soil, unsaturated zone and the aquifer underneath has been made since 2006 to evaluate possible impacts on three experimental plots. For this assessment, monitoring wells and piezometers were installed to determine groundwater flow and water samples were collected for chemical analysis. In the unsaturated zone, tensiometers were installed at different depths to determine flow patterns, while suction lysimeters were used for water sample chemical determinations. The findings show that in the sandy loam plot (Hacienda Real), the unsaturated zone is characterised by low water retention, showing a high transport capacity, while the other two plots of silty composition presented temporal saturation due to La Niña event (2010-2011). The strong La Niña effect on aquifer recharge which would dilute the infiltrated water during the monitoring period and, on the other hand dissolution of possible precipitated salts bringing them back into solution may occur. A slight increase in the concentration of major ions was observed in groundwater (~5% of TDS), which can be attributed to a combination of factors: vinasse dilution produced by water input and hydrochemical processes along with nutrient removal produced by sugar cane uptake. This fact may make the aquifer vulnerable to contamination. PMID:26372944

  2. Assessment of Uncertainty of Radionuclide Transport in the Yucca Mountain Unsaturated Zone: Parametric and Parameter Estimation Uncertainty

    NASA Astrophysics Data System (ADS)

    Pan, F.; Ye, M.; Wu, Y.; Hu, B.; Shirley, C.; Yu, Z.

    2005-12-01

    This study is to assess uncertainty of radionuclide transport in the unsaturated zone at Yucca Mountain. The uncertainty is attributed to parametric uncertainty due to parameter spatial variability and parameter estimation uncertainty when fitting van Genuchten parameters alpha and n based on water retention measurements. The uncertainty assessment is conducted using Monte Carlo simulation and the three-dimensional flow and transport numerical code, TOUGH2, is employed to simulate unsaturated flow and radionuclide transport in the unsaturated zone. Matrix porosity, saturated hydraulic conductivity, sorption coefficient, and van Genuchten alpha and n parameters are treated as statistically homogeneous random variables. Distributions of the first three random parameters are determined based on site measurements. Seven transformations including three transforms from the Johnson system are applied to the measurements and Lilliefors test is used to identify the best transform that renders the transformed data closest to normal distribution. The fitted matrix van Genuchten alpha and n parameters are assumed to follow normal distributions and parameter estimation uncertainty is measured by the covariance matrix obtained from least square analysis. For each model layer, Latin Hypercube Sampling (LHS) method is used to generate 200 realizations random fields, among which matrix porosity is correlated with saturated hydraulic conductivity and van Genuchten alpha and n are correlated also. The correlation between the former two is measured by Spearman rank correlations estimated from site measurements. The Spearman rank correlation of the latter two is calculated from a large number of generated values using MINTAB software based on their estimated means, variances and covariance. 200 Monte Carlo simulations are conducted using the TOUGH2 and convergence of the Monte Carlo results is thoroughly examined. Mean, variances, 5% and 95% percentiles of saturation, capillary

  3. Investigation of groundwater recharge in arid environments through continuous monitoring of water fluxes within the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Kallioras, A.; Reshid, M.; Dietrich, P.; Rausch, R.; Al-Saud, M.; Schuth, C.

    2012-04-01

    For groundwater resources management in arid environments the rate of aquifer replenishment due to groundwater recharge is one of the most important factors and unfortunately also one of the most difficult to derive with sufficient accuracy. In general, the potential evaporation by far exceeds the precipitation limiting groundwater recharge. Unsaturated zone processes play a key role in groundwater recharge as the thickness of the unsaturated zone in arid areas may reach several thenth of meters, compared to millimeters or centimeters of assumed groundwater recharge per year. This indicates the complexity of the problem. Overcoming the field capacity along the infiltration path to initiate downward movement on such a long distance to the groundwater table would require the recharge of tenths or even hundreds of years. Also, precipitation is highly variable in space, time, and intensity and may be followed by hot and dry conditions leading to an alternation of downward and upward movement of water. For this study, field sites in the Kingdom of Saudi Arabia (located app. 200km SW of Riyadh) were selected that represent typical settings for potential groundwater recharge in arid regions, i.e. sand dune areas and wadi beds. In the field campaign vibro-coring techniques applying direct-push technologies (Geoprobe 7720DT) were used to retrieve undisturbed soil sampling down to depths of about 15 m in the unsaturated zone. The drilled boreholes were consequently used for the installation of specially designed flat cable TDR sensors that provide continuous monitoring of the soil moisture content in high vertical resolution. In addition, temperature sensors were installed to monitor temperature fluctuations in the unsaturated zone. We present data on the analyses of soil samples as well as on the measured water content evolution over time as determined by the TDR flat band cables. Results show, that significant changes in water content occurred within the observation time

  4. Stratigraphy of the unsaturated zone and the Snake River Plain aquifer at and near the Idaho National Engineering Laboratory, Idaho

    SciTech Connect

    Anderson, S.R.; Liszewski, M.J.

    1997-08-01

    The unsaturated zone and the Snake River Plain aquifer at and near the Idaho National Engineering Laboratory (INEL) are made up of at least 178 basalt-flow groups, 103 sedimentary interbeds, 6 andesite-flow groups, and 4 rhyolite domes. Stratigraphic units identified in 333 wells in this 890-mile{sup 2} area include 121 basalt-flow groups, 102 sedimentary interbeds, 6 andesite-flow groups, and 1 rhyolite dome. Stratigraphic units were identified and correlated using the data from numerous outcrops and 26 continuous cores and 328 natural-gamma logs available in December 1993. Basalt flows make up about 85% of the volume of deposits underlying the area.

  5. Sensitivity Analysis Of Hydrological Parameters In Modeling FlowAnd Transport In The Unsaturated Zone Of Yucca Mountain

    SciTech Connect

    Zhang, Keni; Wu, Yu-Shu; Houseworth, James E

    2006-02-01

    The unsaturated fractured volcanic deposits at Yucca Mountain in Nevada, USA, have been intensively investigated as a possible repository site for storing high-level radioactive waste. Field studies at the site have revealed that there exist large variabilities in hydrological parameters over the spatial domain of the mountain. Systematic analyses of hydrological parameters using a site-scale three-dimensional unsaturated zone (UZ) flow model have been undertaken. The main objective of the sensitivity analyses was to evaluate the effects of uncertainties in hydrologic parameters on modeled UZ flow and contaminant transport results. Sensitivity analyses were carried out relative to fracture and matrix permeability and capillary strength (van Genuchten {alpha}) through variation of these parameter values by one standard deviation from the base-case values. The parameter variation resulted in eight parameter sets. Modeling results for the eight UZ flow sensitivity cases have been compared with field observed data and simulation results from the base-case model. The effects of parameter uncertainties on the flow fields were evaluated through comparison of results for flow and transport. In general, this study shows that uncertainties in matrix parameters cause larger uncertainty in simulated moisture flux than corresponding uncertainties in fracture properties for unsaturated flow through heterogeneous fractured rock.

  6. Sensitivity analysis of hydrological parameters in modeling flow and transport in the unsaturated zone of Yucca Mountain, Nevada, USA

    NASA Astrophysics Data System (ADS)

    Zhang, Keni; Wu, Yu-Shu; Houseworth, James E.

    2006-12-01

    The unsaturated fractured volcanic deposits at Yucca Mountain in Nevada, USA, have been intensively investigated as a possible repository site for storing high-level radioactive waste. Field studies at the site have revealed that there exist large variabilities in hydrological parameters over the spatial domain of the mountain. Systematic analyses of hydrological parameters using a site-scale three-dimensional unsaturated zone (UZ) flow model have been undertaken. The main objective of the sensitivity analyses was to evaluate the effects of uncertainties in hydrologic parameters on modeled UZ flow and contaminant transport results. Sensitivity analyses were carried out relative to fracture and matrix permeability and capillary strength (van Genuchten α) through variation of these parameter values by one standard deviation from the base-case values. The parameter variation resulted in eight parameter sets. Modeling results for the eight UZ flow sensitivity cases have been compared with field observed data and simulation results from the base-case model. The effects of parameter uncertainties on the flow fields were evaluated through comparison of results for flow and transport. In general, this study shows that uncertainties in matrix parameters cause larger uncertainty in simulated moisture flux than corresponding uncertainties in fracture properties for unsaturated flow through heterogeneous fractured rock.

  7. Steam and air co-injection in removing residual TCE in unsaturated layered sandy porous media

    NASA Astrophysics Data System (ADS)

    Peng, Sheng; Wang, Ning; Chen, Jiajun

    2013-10-01

    Steam and air co-injection is a promising technique for volatile and semi-volatile organic contaminant remediation in heterogeneous porous media. In this study, removal of trichloroethene (TCE) with steam-air co-injection was investigated through a series of 2D sandbox experiments with different layered sand structures, and through numerical simulations. The results show that a layered structure with coarse sand, in which steam and air convection are relatively rapid, resulted in a higher removal rate and a larger removal ratio than those observed in an experiment using finer sand; however, the difference was not significant, and the removal ratios from three experiments ranged from 85% to 94%. Slight downward movement of TCE was observed for Experiment 1 (TCE initially in a fine sand zone encased in a coarse sand), while no such movement was observed for Experiment 2 (TCE initially in two fine sand layers encased in a coarse sand) or 3 (TCE initially in a silty sand zone encased in a coarse sand). Simulations show accumulation of TCE at the interface of the layered sands, which indicates a capillary barrier effect in restraining the downward movement of TCE. This effect is illustrated further by a numerical experiment with homogeneous coarse sand, in which continuous downward TCE movement to the bottom of the sandbox was simulated. Another numerical experiment with higher water saturation was also conducted. The results illustrate a complicated influence of water saturation on TCE removal in a layered sand structure.

  8. Steam and air co-injection in removing residual TCE in unsaturated layered sandy porous media.

    PubMed

    Peng, Sheng; Wang, Ning; Chen, Jiajun

    2013-10-01

    Steam and air co-injection is a promising technique for volatile and semi-volatile organic contaminant remediation in heterogeneous porous media. In this study, removal of trichloroethene (TCE) with steam-air co-injection was investigated through a series of 2D sandbox experiments with different layered sand structures, and through numerical simulations. The results show that a layered structure with coarse sand, in which steam and air convection are relatively rapid, resulted in a higher removal rate and a larger removal ratio than those observed in an experiment using finer sand; however, the difference was not significant, and the removal ratios from three experiments ranged from 85% to 94%. Slight downward movement of TCE was observed for Experiment 1 (TCE initially in a fine sand zone encased in a coarse sand), while no such movement was observed for Experiment 2 (TCE initially in two fine sand layers encased in a coarse sand) or 3 (TCE initially in a silty sand zone encased in a coarse sand). Simulations show accumulation of TCE at the interface of the layered sands, which indicates a capillary barrier effect in restraining the downward movement of TCE. This effect is illustrated further by a numerical experiment with homogeneous coarse sand, in which continuous downward TCE movement to the bottom of the sandbox was simulated. Another numerical experiment with higher water saturation was also conducted. The results illustrate a complicated influence of water saturation on TCE removal in a layered sand structure. PMID:23962760

  9. Modeling the Changes in Unsaturated Hydraulic Properties of Subsurface Media due to Chemical Reactions: A Film Depositional Modeling Approach

    NASA Astrophysics Data System (ADS)

    Freedman, V. L.; Bacon, D. H.; Saripalli, K. P.; Meyer, P. D.

    2001-12-01

    Precipitation and dissolution of minerals in the subsurface can cause a significant reduction in porosity and permeability by plugging pore throats in aquifer and reservoir media. Changes in these two basic properties of the medium also result in significant changes in the remaining 'derived properties' (i.e., relative permeability, fluid-fluid and fluid-solid interfacial areas, pore and particle size distributions) and the constitutive relationships among these properties. Very few published works on modeling the influence of chemical reactions and fluid flow on porosity and permeability account for the spatial and temporal changes in the hydrologic properties on flow and transport. This study reports on the development of a methodology for modeling changes in permeability of unsaturated sub-surface media due to glass and mineral precipitation and dissolution reactions using a film depositional modeling approach. The model is based on the assumption that the mineral precipitate is deposited on the pore walls as a continuous film, causing a reduction in permeability. In this study, the film depositional model is developed for a discrete pore-size distribution, which is determined using the unsaturated hydraulic properties of the porous medium. This facilitates the process of dynamically updating the unsaturated hydraulic parameters used to describe fluid flow through the media. The resulting algorithms are implemented in the multiphase, multicomponent reactive transport code STORM (Sub-surface Transport over Reactive Multiphases). The modeling approach is tested using the Hanford's Immobilized Low Activity Waste (ILAW) repository, where the low-level waste from fuel fabrication activities is being vitrified and emplaced in the sub-surface. Results from simulation of the simultaneous dissolution of low-level glassified waste and secondary mineral precipitation show that the film depositional model based on the Mualem approach reasonably predicts permeability changes

  10. PRZM-2, A MODEL FOR PREDICTING PESTICIDE FATE IN THE CROP ROOT AND UNSATURATED SOIL ZONES: USERS MANUAL FOR RELEASE 2.0

    EPA Science Inventory

    PRZM-2 links two subordinate models--PRZM and VADOFT--in order to predict pesticide transport and transformation down through the crop root and unsaturated zones. RZM is a one-dimensional, finite difference model that accounts for pesticide fate in the crop root zone. his release...

  11. Experimental and modeling of the unsaturated transports of S-metolachlor and its metabolites in glaciofluvial vadose zone solids

    NASA Astrophysics Data System (ADS)

    Sidoli, Pauline; Lassabatere, Laurent; Angulo-Jaramillo, Rafael; Baran, Nicole

    2016-07-01

    The transport of pesticides to groundwater is assumed to be impacted by flow processes and geochemical interactions occurring in the vadose zone. In this study, the transport of S-metolachlor (SMOC) and its two metabolites ESA-metolachlor (MESA) and OXA-metolachlor (MOXA) in vadose zone materials of a glaciofluvial aquifer is studied at laboratory scale. Column experiments are used to study the leaching of a conservative tracer (bromide) and SMOC, MESA and MOXA under unsaturated conditions in two lithofacies, a bimodal gravel (Gcm,b) and a sand (S-x). Tracer experiments showed water fractionation into mobile and immobile compartments more pronounced in bimodal gravel columns. In both lithofacies columns, SMOC outflow is delayed (retardation factor > 2) and mass balance reveals depletion (mass balance of 0.59 and 0.77 in bimodal gravel and sand, respectively). However, complete mass elution associated with retardation factors close to unity shows that there is no adsorption of MESA and MOXA in either lithofacies. SMOC transport is characterized by non-equilibrium sorption and sink term in both bimodal gravel and sand columns. Batch experiments carried out using agitation times consistent with column water residence times confirmed a time-dependence of SMOC sorption and high adsorption rates (> 80%) of applied concentrations. Desorption experiments confirm the irreversibility of a major part of the SMOC adsorption onto particles, corresponding to the sink term in columns. In the bimodal gravel column, SMOC adsorption occurs mainly on reactive particles in contact with mobile water because of flow regionalization whereas in the sand column, there is pesticide diffusion to the immobile water. Such results clearly show that sorption mechanisms in the vadose zone solids below the soil are both solute and contact-time-dependent and are impacted by hydrodynamic conditions. The more rapid transport of MESA and MOXA to the aquifer would be controlled mainly by water flow

  12. A fractal Richards' equation to capture the non-Boltzmann scaling of water transport in unsaturated media.

    PubMed

    Sun, Hongguang; Meerschaert, Mark M; Zhang, Yong; Zhu, Jianting; Chen, Wen

    2013-02-01

    The traditional Richards' equation implies that the wetting front in unsaturated soil follows Boltzmann scaling, with travel distance growing as the square root of time. This study proposes a fractal Richards' equation (FRE), replacing the integer-order time derivative of water content by a fractal derivative, using a power law ruler in time. FRE solutions exhibit anomalous non-Boltzmann scaling, attributed to the fractal nature of heterogeneous media. Several applications are presented, fitting the FRE to water content curves from previous literature. PMID:23794783

  13. Methyl tert-butyl ether degradation in the unsaturated zone and the relation between MTBE in the atmosphere and shallow groundwater

    USGS Publications Warehouse

    Baehr, A.L.; Charles, E.G.; Baker, R.J.

    2001-01-01

    Atmospheric methyl tert-butyl ether (MTBE) concentrations in southern New Jersey generally exceeded concentrations in samples taken from the unsaturated zone. A simple unsaturated zone transport model indicates that MTBE degradation can explain the attenuation with half-lives from a few months to a couple of years. Tert-butyl alcohol (TBA), a possible degradation product of MTBE, was detected in unsaturated-zone samples at concentrations exceeding atmospheric levels at some sites, suggesting the possible conversion of MTBE to TBA. At sites where MTBE was detected in shallow groundwater, the concentration was typically higher than the overlying unsaturated-zone concentration. This observation is consistent with outgassing from the aquifer and combined with the unsaturated-zone attenuation suggests some of the MTBE detections in shallow groundwater are nonatmospheric in origin, coming from leaking tanks, road runoff, or other sources. The identification of sources of MTBE in groundwater and attenuation mechanisms through the hydrologic cycle is critical in developing an understanding of the long-term effect of MTBE releases.

  14. Potential for ground-water contamination from movement of wastewater through the unsaturated zone, upper Mojave River Basin, California

    USGS Publications Warehouse

    Umari, A.M.; Martin, P.M.; Schroeder, R.A.; Duell, L.F., Jr.; Fay, R.G.

    1993-01-01

    Septic-tank wastewater disposed in 30-foot-deep seepage pits (dry wells) at 46,000 residences is estimated to equal 18 percent of the natural recharge to the sole-source aquifer in the rapidly developing upper Mojave River Basin (Victor Valley) in the high desert northeast of Los Angeles. Vertical rates of movement of the wastewater wetting front through the unsaturated zone at three newly occupied residences ranged from 0.07 to 1.0 foot per day. These rates translate to traveltimes of several months to several years for the wastewater wetting front to reach the water table and imply that wastewater from many disposal systems already has reached the water table, which averages about 150 feet below land surface in the Victor Valley. As wastewater percolates from seepage pits into the adjacent unsaturated zone, the nitrogen present in reduced form is rapidly converted to nitrate. Analyses on soil-core extracts and soil moisturefrom suction lysimeters installed beneath the seepage pits at eight residences showed that nitrate concentrations and nitrate/ chloride ratios generally become lower with increasing depth. The intervals of greatest decline seemed to coincide with finer soil texture or were near the water table. Nitrate-reducing bacteria were tested for and found to be present in soil cores from two residences. Sparse nitrogen-15 data from suction lysimeters at one of these residences, where thenitrate concentration decreased by about one-half at a depth of 200 feet, indicate that the nitrate decline was accompanied by nitrogen-15 enrichment in the residual nitrate with an isotope-separation factor of about -10 permil. Despite the potential input of abundant nitrogen with the domestic wastewater recharge, nitrate concentrations in the area's ground water are generally low. The absence of high nitrate concentrations in the ground water is consistent with the existence of denitrification, a microbial nitrogen-removal mechanism, as wastewater moves through the

  15. Determination of Transport Parameters in Unsaturated Zone by Tracer Experiment in the Porous Aquifer located at Ljubljana, Slovenia

    NASA Astrophysics Data System (ADS)

    Vidmar, S.; Cencur Curk, B.

    2009-04-01

    The gravel sandy aquifer of Ljubljansko polje is the source of drinking water for nearly 300.000 inhabitants of the Ljubljana city and vicinity. There are two main waterworks: Kleče and Hrastje. The plain area of Ljubljansko polje is a tectonic sink and consists of river sediments that can reach in thickness more than 100 m in the deepest part. The bedrock is the impermeable permocarbonic clayey shale, mudstones and sandstones. The hydraulic conductivity of Ljubljansko polje sediments is very good, from 10-2 m/s in the central part to 3.7•10-3 m/s on the borders of the plain. The average groundwater level is 20 m below surface. A numerical groundwater flow model was established for the wider area of the Ljubljansko polje aquifer. The fore mentioned model was not calibrated on solute transport parameters but only on water levels and this lead to unreliability in the transport model and its predictions of pollution scenarios. The transport model needs to calculate reliable scenarios of pollution dispersion, which can only be achieved with the application of real transport parameters. Human activities in the area of the Hrastje waterworks of Ljubljana threaten to degrade groundwater quality. For this reason several tracer experiments were carried out in the past. Despite a great risk, the experiments were performed on the catchment area of the Hrastje waterworks, inside the second water protection zone. During the experiments the water from Hrastje waterworks was still in use for drinking water supply. The tracer experiments were carried out in order to determine the solute transport parameters such as advection, dispersion and sorption. The research proved that the tracers could be used safely on sensitive area and that the researchers are capable and qualified to carry it out with a highest level of security. Since none of the past tracer experiments, carried out in the same area, gave us any detailed information on pollutant spreading in unsaturated zone a new

  16. Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes

    NASA Astrophysics Data System (ADS)

    Sprenger, M.; Volkmann, T. H. M.; Blume, T.; Weiler, M.

    2015-06-01

    Determining the soil hydraulic properties is a prerequisite to physically model transient water flow and solute transport in the vadose zone. Estimating these properties by inverse modelling techniques has become more common within the last 2 decades. While these inverse approaches usually fit simulations to hydrometric data, we expanded the methodology by using independent information about the stable isotope composition of the soil pore water depth profile as a single or additional optimization target. To demonstrate the potential and limits of this approach, we compared the results of three inverse modelling strategies where the fitting targets were (a) pore water isotope concentrations, (b) a combination of pore water isotope concentrations and soil moisture time series, and (c) a two-step approach using first soil moisture data to determine water flow parameters and then the pore water stable isotope concentrations to estimate the solute transport parameters. The analyses were conducted at three study sites with different soil properties and vegetation. The transient unsaturated water flow was simulated by solving the Richards equation numerically with the finite-element code of HYDRUS-1D. The transport of deuterium was simulated with the advection-dispersion equation, and a modified version of HYDRUS was used, allowing deuterium loss during evaporation. The Mualem-van Genuchten and the longitudinal dispersivity parameters were determined for two major soil horizons at each site. The results show that approach (a), using only the pore water isotope content, cannot substitute hydrometric information to derive parameter sets that reflect the observed soil moisture dynamics but gives comparable results when the parameter space is constrained by pedotransfer functions. Approaches (b) and (c), using both the isotope profiles and the soil moisture time series, resulted in good simulation results with regard to the Kling-Gupta efficiency and good parameter

  17. A site-scale model for fluid and heat flow in the unsaturated zone of Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Wu, Yu-Shu; Haukwa, Charles; Bodvarsson, G. S.

    1999-05-01

    A three-dimensional unsaturated-zone numerical model has been developed to simulate flow and distribution of moisture, gas and heat at Yucca Mountain, Nevada, a potential repository site for high-level radioactive waste. The model takes into account the simultaneous flow dynamics of liquid water, vapor, air and heat in the highly heterogeneous, fractured porous rock in the unsaturated zone (UZ). This model is intended for use in the prediction of the current and future conditions in the UZ so as to aid in the assessment of the system performance of the proposed repository. The modeling approach is based on a mathematical formulation of coupled multiphase, multicomponent fluid and heat flow through porous and fractured rock. Fracture and matrix flow is treated using both dual-permeability and effective-continuum modeling approaches. The model domain covers a total area of approximately 43 km 2, and uses the land surface and the water table as its top and bottom boundaries. In addition, site-specific data, representative surface infiltration, and geothermal conditions are incorporated into the model. The reliability and accuracy of the model have been the subject of a comprehensive model calibration study, in which the model was calibrated against measured data, including liquid saturation, water potential and temperature. It has been found that the model is generally able to reproduce the overall system behavior at Yucca Mountain with respect to moisture profiles, pneumatic pressure variations in different geological units, and ambient geothermal conditions.

  18. Preliminary 3-D site-scale studies of radioactive colloid transortin the unsaturated zone at Yucca Mountain, Nevada

    SciTech Connect

    Moridis, G.J.; Hu, Q.; Wu, Y.-S.; Bodvarsson, G.S.

    2001-09-01

    The U.S: Department of Energy is actively investigating the technical feasibility of permanent disposal of high-level nuclear waste in a repository to be situated in the unsaturated zone at Yucca Mountain, Nevada. In this study we investigate, by means of numerical simulation, the transport of radioactive colloids under ambient conditions from the potential repository horizon to the water table. The site hydrology and the effects of the spatial distribution of hydraulic and transport properties in the Yucca Mountain subsurface are considered. The study of migration and retardation of colloids accounts for the complex processes in the unsaturated zone of Yucca Mountain, and includes advection, diffusion, hydrodynamic dispersion, kinetic colloid filtration, colloid straining, and radioactive decay. The results of the study indicate that the most important factors affecting colloid transport are the subsurface geology and site hydrology, i.e., the presence of faults (they dominate and control transport), fractures (the main migration pathways), and the relative distribution of zeolitic and vitric tuffs. The transport of colloids is strongly influenced by their size (as it affects diffusion into the matrix, straining at hydrogeologic unit interfaces, and transport velocity) and by the parameters of the kinetic-filtration model used for the simulations. Arrival times at the water table decrease with an increasing colloid size because of smaller diffusion, increased straining, and higher transport velocities. The importance of diffusion as a retardation mechanism increases with a decreasing colloid size, but appears to be minimal in large colloids.

  19. Preliminary 3-D site-scale studies of radioactive colloid transport in the unsaturated zone at Yucca Mountain, Nevada.

    PubMed

    Moridis, G J; Hu, Q; Wu, Y-S; Bodvarsson, G S

    2003-02-01

    The U.S. Department of Energy (DOE) is actively investigating the technical feasibility of permanent disposal of high-level nuclear waste in a repository to be situated in the unsaturated zone (UZ) at Yucca Mountain (YM), Nevada. In this study we investigate, by means of numerical simulation, the transport of radioactive colloids under ambient conditions from the potential repository horizon to the water table. The site hydrology and the effects of the spatial distribution of hydraulic and transport properties in the Yucca Mountain subsurface are considered. The study of migration and retardation of colloids accounts for the complex processes in the unsaturated zone of Yucca Mountain, and includes advection, diffusion, hydrodynamic dispersion, kinetic colloid filtration, colloid straining, and radioactive decay. The results of the study indicate that the most important factors affecting colloid transport are the subsurface geology and site hydrology, i.e., the presence of faults (they dominate and control transport), fractures (the main migration pathways), and the relative distribution of zeolitic and vitric tuffs. The transport of colloids is strongly influenced by their size (as it affects diffusion into the matrix, straining at hydrogeologic unit interfaces, and transport velocity) and by the parameters of the kinetic-filtration model used for the simulations. Arrival times at the water table decrease with an increasing colloid size because of smaller diffusion, increased straining, and higher transport velocities. The importance of diffusion as a retardation mechanism increases with a decreasing colloid size, but appears to be minimal in large colloids. PMID:12504362

  20. Hydrologic evaluation methodology for estimating water movement through the unsaturated zone at commercial low-level radioactive waste disposal sites

    SciTech Connect

    Meyer, P.D.; Rockhold, M.L.; Nichols, W.E.; Gee, G.W.

    1996-01-01

    This report identifies key technical issues related to hydrologic assessment of water flow in the unsaturated zone at low-level radioactive waste (LLW) disposal facilities. In addition, a methodology for incorporating these issues in the performance assessment of proposed LLW disposal facilities is identified and evaluated. The issues discussed fall into four areas: estimating the water balance at a site (i.e., infiltration, runoff, water storage, evapotranspiration, and recharge); analyzing the hydrologic performance of engineered components of a facility; evaluating the application of models to the prediction of facility performance; and estimating the uncertainty in predicted facility performance. To illustrate the application of the methodology, two examples are presented. The first example is of a below ground vault located in a humid environment. The second example looks at a shallow land burial facility located in an arid environment. The examples utilize actual site-specific data and realistic facility designs. The two examples illustrate the issues unique to humid and arid sites as well as the issues common to all LLW sites. Strategies for addressing the analytical difficulties arising in any complex hydrologic evaluation of the unsaturated zone are demonstrated.

  1. TRANSPORT AND DEPOSITION OF METABOLICALLY ACTIVE AND STATIONARY PHASE DEINOCOCCUS RADIODURANS IN UNSATURATED POROUS MEDIA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Bioremediation is a cost efficient clean-up technique that involves the use of metabolically active bacteria to degrade recalcitrant pollutants. To further develop this technique it is important to understand the migration and deposition behaviour of metabolically active bacteria in unsaturated soil...

  2. Geohydrology of the unsaturated zone at the burial site for low-level radioactive waste near Beatty, Nye County, Nevada

    USGS Publications Warehouse

    Nichols, W.D.

    1986-01-01

    Low-level radioactive solid waste has been buried in trenches at a site near Beatty, Nevada, since 1962. In 1976, as part of a national program, the U.S. Geological Survey began a study of the geohydrology of the waste burial site to provide a basis for estimating the potential for radionuclide migration in the unsaturated zone beneath the waste burial trenches. Data collected include meteorological information for calibration of a long-term water budget analysis, soil moisture profiles, soil water potentials, and hydraulic properties of representative unsaturated sediment samples to a depth of about 10 m. The waste burial facility is in the northern Amargosa Desert about 170 km northwest of Las Vegas, NV. The region is arid; mean annual precipitation at Lathrop Wells, 30 km south of the site, is only 7.4 cm. The mean daily maximum temperature at Lathrop Wells in July, the hottest month, is 37 C. The site is underlain by poorly stratified deposits of gravelly or silty sand and sandy gravel, and thick beds of clayey sediments. The total thickness of valley fill deposits beneath the site is about 175 m; the unsaturated zone is about 85 m thick. Volumetric soil moisture to depths of 4 m ranges from 4% to 10%, but commonly is in the range from 6% to 8%. Soil water potential, measured to depths of 3 to 10 m, ranged from -10 to -70 bars. Unsaturated hydraulic conductivity computed from laboratory analyses of representative samples ranges from 10 to the -13th power to 10 to the -4th power cm/day. Evaporation studies over a 2-yr period were used to calibrate a numerical procedure for analyzing long-term precipitation data and estimating annual water budgets during the 15-yr period 1962-76. This analysis (1) demonstrated that a potential exists for deep percolation (> 2 m), despite high annual evaporation demands, and (2) provided predictions of the time of yr and the antecedent conditions which enhance the probability of deep percolation. Soil moisture profiles obtained

  3. Mixing Zones and Mineral Precipitation Dynamics in Porous Media

    NASA Astrophysics Data System (ADS)

    Gebrehiwet, T.; Henrikson, J.; Guo, L.; Fox, D. T.; Huang, H.; Fujita, Y.; Tu, L.

    2011-12-01

    Precipitation of mineral phases in subsurface environments involves coupling between reactant transport and changes in media properties that control transport. Chemical gradients within mixing zones will determine the rates and products of reactions, which in turn can modify the permeability and flow paths within the porous media. This reaction-transport coupling is being studied using double diffusion experiments and reactive transport modeling, with calcium carbonate and calcium phosphate as the model mineral systems. In particular we are investigating: (1) the interplay between permeability modifications and reactions that can change local chemical conditions, hydrodynamic conditions, and therefore the rate of precipitation, (2) narrowing ("focusing") of the precipitation zone, and (3) migration of the precipitation zone associated with asymmetry across the mixing zone with respect to precipitation rates and/or local chemical conditions. Experiments are being conducted in hydrogel (polyacrylamide) and granular (glass beads and fine-grained sand) media. Gels were used to investigate the role of diffusion alone on the structure of precipitation zones. We observed differences between carbonate and phosphate systems with respect to the induction period for precipitation, and the position and migration of the precipitation zone. One interesting observation was that multiple precipitation bands are produced in the calcium phosphate system, while no clear banding has been observed in the calcium carbonate system. Initial reactive transport simulations that couple precipitation kinetics with reactant transport and mixing appear consistent with the experimental observations. Precipitation band width and position were found to change with time, and precipitation appeared to slow subsequent reactions at the mixing interfaces. The induction time, spacing between the precipitation bands and band width in the calcium phosphate system were influenced by pH, saturation state

  4. Seasonal variations and cycling of nitrous oxide using nitrogen isotopes and concentrations from an unsaturated zone of a floodplain

    NASA Astrophysics Data System (ADS)

    Bill, M.; Conrad, M. E.; Kolding, S.; Williams, K. H.; Tokunaga, T. K.

    2014-12-01

    Nitrous oxide (N2O) concentrations and isotope ratios of 15N to 14N of N2O in the vadose zone mainly depend on atmospheric deposition, symbiotic or non-symbiotic N2 fixation, and nitrification/denitrification processes in underlying groundwater. In an effort to quantify N2O seasonal variations, cycling and N budgets in an alluvial aquifer in western Colorado (Rifle, CO), the concentrations and nitrogen stable isotopes of N2O within the pore space of partially saturated sediments have been monitored over the 2013-2014 years. Vertically resolved profiles spanning from 0m to 3m depth were sampled at 0.5m increments at a periodicity of one month. At each of the profile locations, N2O concentrations decreased from 3m depth to the surface. The maximum concentrations were observed at the interface between the unsaturated zone and groundwater, with minimum values observed in the near surface samples. The d15N values tend to increase from the unsaturated zone/groundwater interface to the surface. Both variation of N2O concentrations and d15N values suggest that denitrification is the main contribution to N2O production and both parameters exhibited a strong seasonal variation. The maximum concentrations (~10ppmv) were observed at the beginning of summer, during the annual maximum in water table elevation. The minimum N2O concentrations were observed in the period from January to May and coincided with low water table elevations. Additionally, nitrogen concentrations and d15N values of the shallowest sediments within the vertical profiles do not show variation, suggesting that the main source of N2O is associated with groundwater denitrification, with the shallower, partially saturated sediments acting as a sink for N2O.

  5. Influences of the unsaturated, saturated, and riparian zones on the transport of nitrate near the Merced River, California, USA

    USGS Publications Warehouse

    Domagalski, J.L.; Phillips, S.P.; Bayless, E.R.; Zamora, C.; Kendall, C.; Wildman, R.A.; Hering, J.G.

    2008-01-01

    Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50-100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N2 in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area. ?? Springer-Verlag 2007.

  6. Influences of the unsaturated, saturated, and riparian zones on the transport of nitrate near the Merced River, California, USA

    NASA Astrophysics Data System (ADS)

    Domagalski, Joseph L.; Phillips, Steven P.; Bayless, E. Randall; Zamora, Celia; Kendall, Carol; Wildman, Richard A.; Hering, Janet G.

    2008-06-01

    Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50-100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N2 in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.

  7. Balancing practicality and hydrologic realism: Insights from applications of a parsimonious model of unsaturated-zone preferential flow

    NASA Astrophysics Data System (ADS)

    Mirus, B. B.; Perkins, K. S.; Nimmo, J. R.

    2011-12-01

    Simple assessments are often needed to inform local land-management decisions. Preferential flow, a crucial process in many land-management decisions, presents a considerable challenge to the parameterization and evaluation of commonly used hydrologic models. Traditional unsaturated flow theory (i.e., Richards equation) does not accurately represent the physics of preferential flow and often underestimates the arrival time and magnitude of fluxes when applied in situations where preferential flow is important. Another shortcoming of traditional modeling approaches is the considerable data required to characterize the distribution of subsurface hydraulic properties. A source-responsive model has been developed based on film-flow theory to provide more realistic approximations of unsaturated-zone preferential flow when limited data and site characterization are available. The term source-responsive is used to describe the sensitivity of preferential flow to changing conditions at the source of water input, which are typically better quantified than hydraulic properties. We present applications of this parsimonious model for sites in Idaho and Nevada with heterogeneous vadose zones (40 m and 1000 m in thickness, respectively) where radionuclide contamination poses a threat to groundwater quality. Despite differences in input data for each application, results from both applications provide reasonable flux estimates, which are useful for characterizing worst-case scenarios for advective transport of conservative contaminants. We contrast the results for the two applications in terms of the data employed for each and discuss the advantages of the model parameterization, which relies heavily on the quantity and timing of net infiltration. There are several opportunities for improvements in model performance, but these involve greater model complexity with a corresponding increase in free parameters and data requirements. The tradeoff between hydrologic realism and

  8. Development of methods to evaluate uranium distribution coefficients in unsaturated media

    SciTech Connect

    Sautman, M.T.; Simonson, S.A.

    1993-12-31

    To date, batch sorption and dynamic column experiments have been performed for many elements as part of site characterization programs. These experiments were often conducted with samples having relatively high liquid/solid ratios (in some cases the solid volume was much smaller than the solution volume). The development of methods for measuring sorption parameters at low liquid/solid ratios was undertaken to attempt to judge whether or not results of saturated experiments are valid for use in performance assessments of sites located in unsaturated rocks. The amount of hydrologic saturation can affect the ionic strength, pH, and redox potential which can in turn affect sorption. In addition, the presence of the gas phase may affect the amount of wetting occurring on the solid`s surface. This paper describes experimental procedures which were developed to evaluate the sorption of uranium by silica sand at predetermined levels of unsaturation.

  9. Combined analytical/numerical approaches to solving fluid flow problems in the unsaturated zone at Yucca Mountain

    SciTech Connect

    Zimmerman, R.W.; Bodvarsson, G.S.

    1990-01-01

    Various analytical and numerical approaches are presented for the study of unsaturated flow processes in the vicinity of the Yucca Mountain, Nevada, the proposed site of an underground radioactive waste repository. Approximate analytical methods are used to study absorption of water from a saturated fracture into the adjacent rock. These solutions are incorporated into a numerical simulator as fracture/matrix interaction terms to treat problems such as flow along a fracture with transverse leakage into the matrix. An automatic fracture/matrix mesh generator is described; it allows for more efficient mesh generation for fractured/porous media, and consequently leads to large savings in computational time and cost. 21 refs., 6 figs.

  10. THE INFLUENCE OF REPOSITORY THERMAL LOAD ON MULTIPHASE FLOW AND HEAT TRANSFER IN THE UNSATURATED ZONE OF YUCCA MOUNTAIN

    SciTech Connect

    Yu-Shu Wu, Sumit Mukhopadhyay, Keni Zhang, and G. S. Bodvarsson

    2006-04-16

    This paper investigates the impact of proposed repository thermal-loading on mountain-scale flow and heat transfer in the unsaturated fractured rock of Yucca Mountain, Nevada. In this context, a model has been developed to study the coupled thermal-hydrological (TH) processes at the scale of the entire Yucca Mountain. This mountain-scale TH model implements the current geological framework and hydrogeological conceptual models, and incorporates the latest rock thermal and hydrological properties. The TH model consists of a two-dimensional north-south vertical cross section across the entire unsaturated zone model domain and uses refined meshes near and around the proposed repository block, based on the current repository design, drift layout, thermal loading scenario, and estimated current and future climatic conditions. The model simulations provide insights into thermally affected liquid saturation, gas- and liquid-phase fluxes, and elevated water and rock temperature, which in turn allow modelers to predict the changes in water flux driven by evaporation/condensation processes, and drainage between drifts.

  11. Effect of Particle-Scale Heterogeneity on Uranium(VI) Transport in Unsaturated Porous Media

    SciTech Connect

    Wellman, Dawn M.; Gamerdinger, Amy P.; Kaplan, Daniel I.; Serne, R. Jeffrey

    2008-01-23

    Uranium (VI) sorption and transport was evaluated in mixtures of silt loam and coarse sand sediments using traditional static batch sorption, saturated column, and unsaturated centrifugation experiments to evaluate the association of mobile and immobile water domains with particles of different size and surface reactivity. Exclusion of conservative tracers and a decrease in uranium sorption compared to what was predicted by the Kd-mass-avg value observed in sediment mixtures where the mass fraction of silt loam was 10%. This is consistent with behavior that was previously reported for coarse and fine sand separates. No exclusion of the conservative tracer, as predicted for the moderate water content range, was measured during unsaturated transport in sediment mixtures that contained 30% or more silt loam by mass. However, sorption was greater than predicted based on the Kd-mass-avg value, which suggests the fine-textured silt was in contact with the mobile water domain. This is the first evidence linking sorption to transport in a particular water domain. Results of this investigation demonstrate the interaction between the geochemical and hydrodynamic processes has a profound effect on transport in unsaturated sediments. In particular, analyses of the data from the experiments on sediment mixtures illustrate how the hydrodynamic conditions have a significant impact on the breakthrough of sorptive solutes. Definition of the fraction of mobile water was especially important for defining the front of the BTC, which is integral to predicting the arrival time of solutes at a particular depth/location in the sediment.

  12. Using Local Second Gradient Model and Shear Strain Localisation to Model the Excavation Damaged Zone in Unsaturated Claystone

    NASA Astrophysics Data System (ADS)

    Pardoen, Benoît; Levasseur, Séverine; Collin, Frédéric

    2015-03-01

    The drilling of galleries induces damage propagation in the surrounding medium and creates, around them, the excavation damaged zone (EDZ). The prediction of the extension and fracture structure of this zone remains a major issue, especially in the context of underground nuclear waste storage. Experimental studies on geomaterials indicate that localised deformation in shear band mode usually appears prior to fractures. Thus, the excavation damaged zone can be modelled by considering the development of shear strain localisation bands. In the classical finite element framework, strain localisation suffers a mesh-dependency problem. Therefore, an enhanced model with a regularisation method is required to correctly model the strain localisation behaviour. Among the existing methods, we choose the coupled local second gradient model. We extend it to unsaturated conditions and we include the solid grain compressibility. Furthermore, air ventilation inside underground galleries engenders a rock-atmosphere interaction that could influence the damaged zone. This interaction has to be investigated in order to predict the damaged zone behaviour. Finally, a hydro-mechanical modelling of a gallery excavation in claystone is presented and leads to a fairly good representation of the EDZ. The main objectives of this study are to model the fractures by considering shear strain localisation bands, and to investigate if an isotropic model accurately reproduces the in situ measurements. The numerical results provide information about the damaged zone extension, structure and behaviour that are in very good agreement with in situ measurements and observations. For instance, the strain localisation bands that develop in chevron pattern during the excavation and rock desaturation, due to air ventilation, are observed close to the gallery.

  13. Colloid Transport in Unsaturated Porous Media: 3D Visualization Using Synchrotron X-Ray Microtomography

    NASA Astrophysics Data System (ADS)

    Brueck, C. L.; Meisenheimer, D.; Wildenschild, D.

    2015-12-01

    Understanding the mechanisms controlling colloid transport and deposition in the vadose zone is an important step in protecting our water resources. Not only may these particles themselves be undesirable contaminants, but they can also aid in the transport of smaller, molecular-scale contaminants by chemical attachment. In this research, we examined the influence that air-water interfaces (AWI) and air-water-solid contact lines (AWS) have on colloid deposition and mobilization in three-dimensional systems. We used x-ray microtomography to visualize the transport of hydrophobic colloids as they move through a partially saturated glass bead pack. Drainage and imbibition experiments were conducted using syringe pumps to control the flow of a colloid suspension through the porous media at 0.6 mL/hr. The high ionic strength fluid was adjusted to a pH of 9.5 and a concentration of 1.0 mol/L KI. During the drainage and imbibition, the flow was periodically halted and allowed to equilibrate before collecting the microtomography scans. Dopants were used to enhance the contrast between the four phases (water, air, beads, and colloids), including potassium iodide dissolved in the fluid, and an outer layer of silver coating the colloids. We hypothesized that AWIs and AWSs will scour and mobilize a significant percentage of colloids, and therefore reduce the concentration of colloids along the vertical profile of the column. The concentration of potassium iodide, and thus the ionic strength, necessary for adequate image segmentation was also explored in separate experiments so that the influence of ionic strength on colloid deposition and mobilization can be studied.

  14. Effect of hydrofracking fluid on colloid transport in the unsaturated zone.

    PubMed

    Sang, Wenjing; Stoof, Cathelijne R; Zhang, Wei; Morales, Verónica L; Gao, Bin; Kay, Robert W; Liu, Lin; Zhang, Yalei; Steenhuis, Tammo S

    2014-07-15

    Hydraulic fracturing is expanding rapidly in the US to meet increasing energy demand and requires high volumes of hydrofracking fluid to displace natural gas from shale. Accidental spills and deliberate land application of hydrofracking fluids, which return to the surface during hydrofracking, are common causes of environmental contamination. Since the chemistry of hydrofracking fluids favors transport of colloids and mineral particles through rock cracks, it may also facilitate transport of in situ colloids and associated pollutants in unsaturated soils. We investigated this by subsequently injecting deionized water and flowback fluid at increasing flow rates into unsaturated sand columns containing colloids. Colloid retention and mobilization was measured in the column effluent and visualized in situ with bright field microscopy. While <5% of initial colloids were released by flushing with deionized water, 32-36% were released by flushing with flowback fluid in two distinct breakthrough peaks. These peaks resulted from 1) surface tension reduction and steric repulsion and 2) slow kinetic disaggregation of colloid flocs. Increasing the flow rate of the flowback fluid mobilized an additional 36% of colloids, due to the expansion of water filled pore space. This study suggests that hydrofracking fluid may also indirectly contaminate groundwater by remobilizing existing colloidal pollutants. PMID:24905470

  15. Effect of Hydrofracking Fluid on Colloid Transport in the Unsaturated Zone

    PubMed Central

    2014-01-01

    Hydraulic fracturing is expanding rapidly in the US to meet increasing energy demand and requires high volumes of hydrofracking fluid to displace natural gas from shale. Accidental spills and deliberate land application of hydrofracking fluids, which return to the surface during hydrofracking, are common causes of environmental contamination. Since the chemistry of hydrofracking fluids favors transport of colloids and mineral particles through rock cracks, it may also facilitate transport of in situ colloids and associated pollutants in unsaturated soils. We investigated this by subsequently injecting deionized water and flowback fluid at increasing flow rates into unsaturated sand columns containing colloids. Colloid retention and mobilization was measured in the column effluent and visualized in situ with bright field microscopy. While <5% of initial colloids were released by flushing with deionized water, 32–36% were released by flushing with flowback fluid in two distinct breakthrough peaks. These peaks resulted from 1) surface tension reduction and steric repulsion and 2) slow kinetic disaggregation of colloid flocs. Increasing the flow rate of the flowback fluid mobilized an additional 36% of colloids, due to the expansion of water filled pore space. This study suggests that hydrofracking fluid may also indirectly contaminate groundwater by remobilizing existing colloidal pollutants. PMID:24905470

  16. Unsaturated zone characterization of the Area 5 Radioactive Waste Management Site

    SciTech Connect

    Daffern, D.D.; Ebeling, L.L.; Cox, W.B.

    1990-11-01

    Six undisturbed soil samples of near-surface sediments were collected from the Nevada Test Site (NTS) Radioactive Waste Management Site (RWMS) for physical and hydrologic characterization in the laboratory. Of these samples, three were obtained from the wall of Pit No. 3 and three from the floor. Physical properties measured on all samples were dry bulk density ({rho}{sub b}) and solid particle density ({rho}{sub s}). Average dry bulk densities for the wall and floor samples were 1.47 g/cm{sup 3} and 1.45 g/cm{sup 3}, while solid particle densities were 2.34 g/cc and 2.53 g/cc, respectively. Based on these values, the average porosity for the wall samples was computed to be 0.372 and for the floor samples, 0.427. Moisture content-pressure head relations for each sample were determined using the pressure plate method. The moisture characteristic curves generated from these data have shapes similar to those of a silty sand, with volumetric moisture contents of less than 7% at 33.4 bars. Unsaturated hydraulic conductivity was estimated using the computer model of van Genuchten (1978), which is based on the theoretical developments of Mualem (1976). Results indicate that at near-surface in situ moisture contents, the unsaturated hydraulic conductivity for both wall and floor samples is less than 10{sup {minus}8} cm/sec. 15 refs., 12 figs., 4 tabs.

  17. Experimental and modeling of the unsaturated transports of S-metolachlor and its metabolites in glaciofluvial vadose zone solids.

    PubMed

    Sidoli, Pauline; Lassabatere, Laurent; Angulo-Jaramillo, Rafael; Baran, Nicole

    2016-07-01

    The transport of pesticides to groundwater is assumed to be impacted by flow processes and geochemical interactions occurring in the vadose zone. In this study, the transport of S-metolachlor (SMOC) and its two metabolites ESA-metolachlor (MESA) and OXA-metolachlor (MOXA) in vadose zone materials of a glaciofluvial aquifer is studied at laboratory scale. Column experiments are used to study the leaching of a conservative tracer (bromide) and SMOC, MESA and MOXA under unsaturated conditions in two lithofacies, a bimodal gravel (Gcm,b) and a sand (S-x). Tracer experiments showed water fractionation into mobile and immobile compartments more pronounced in bimodal gravel columns. In both lithofacies columns, SMOC outflow is delayed (retardation factor>2) and mass balance reveals depletion (mass balance of 0.59 and 0.77 in bimodal gravel and sand, respectively). However, complete mass elution associated with retardation factors close to unity shows that there is no adsorption of MESA and MOXA in either lithofacies. SMOC transport is characterized by non-equilibrium sorption and sink term in both bimodal gravel and sand columns. Batch experiments carried out using agitation times consistent with column water residence times confirmed a time-dependence of SMOC sorption and high adsorption rates (>80%) of applied concentrations. Desorption experiments confirm the irreversibility of a major part of the SMOC adsorption onto particles, corresponding to the sink term in columns. In the bimodal gravel column, SMOC adsorption occurs mainly on reactive particles in contact with mobile water because of flow regionalization whereas in the sand column, there is pesticide diffusion to the immobile water. Such results clearly show that sorption mechanisms in the vadose zone solids below the soil are both solute and contact-time-dependent and are impacted by hydrodynamic conditions. The more rapid transport of MESA and MOXA to the aquifer would be controlled mainly by water flow

  18. Field-scale sulfur hexafluoride tracer experiment to understand long distance gas transport in the deep unsaturated zone

    USGS Publications Warehouse

    Walvoord, Michelle Ann; Andraski, Brian; Green, Christopher T.; Stonestrom, David A.; Striegl, Rob

    2014-01-01

    A natural gradient SF6 tracer experiment provided an unprecedented evaluation of long distance gas transport in the deep unsaturated zone (UZ) under controlled (known) conditions. The field-scale gas tracer test in the 110-m-thick UZ was conducted at the U.S. Geological Survey’s Amargosa Desert Research Site (ADRS) in southwestern Nevada. A history of anomalous (theoretically unexpected) contaminant gas transport observed at the ADRS, next to the first commercial low-level radioactive waste disposal facility in the United States, provided motivation for the SF6 tracer study. Tracer was injected into a deep UZ borehole at depths of 15 and 48 m, and plume migration was observed in a monitoring borehole 9 m away at various depths (0.5–109 m) over the course of 1 yr. Tracer results yielded useful information about gas transport as applicable to the spatial scales of interest for off-site contaminant transport in arid unsaturated zones. Modeling gas diffusion with standard empirical expressions reasonably explained SF6 plume migration, but tended to underpredict peak concentrations for the field-scale experiment given previously determined porosity information. Despite some discrepancies between observations and model results, rapid SF6 gas transport commensurate with previous contaminant migration was not observed. The results provide ancillary support for the concept that apparent anomalies in historic transport behavior at the ADRS are the result of factors other than nonreactive gas transport properties or processes currently in effect in the undisturbed UZ.

  19. A geostatistical modeling study of the effect of heterogeneity on radionuclide transport in the unsaturated zone, Yucca Mountain.

    PubMed

    Viswanathan, Hari S; Robinson, Bruce A; Gable, Carl W; Carey, James W

    2003-01-01

    Retardation of certain radionuclides due to sorption to zeolitic minerals is considered one of the major barriers to contaminant transport in the unsaturated zone of Yucca Mountain. However, zeolitically altered areas are lower in permeability than unaltered regions, which raises the possibility that contaminants might bypass the sorptive zeolites. The relationship between hydrologic and chemical properties must be understood to predict the transport of radionuclides through zeolitically altered areas. In this study, we incorporate mineralogical information into an unsaturated zone transport model using geostatistical techniques to correlate zeolitic abundance to hydrologic and chemical properties. Geostatistical methods are used to develop variograms, kriging maps, and conditional simulations of zeolitic abundance. We then investigate, using flow and transport modeling on a heterogeneous field, the relationship between percent zeolitic alteration, permeability changes due to alteration, sorption due to alteration, and their overall effect on radionuclide transport. We compare these geostatistical simulations to a simplified threshold method in which each spatial location in the model is assigned either zeolitic or vitric properties based on the zeolitic abundance at that location. A key conclusion is that retardation due to sorption predicted by using the continuous distribution is larger than the retardation predicted by the threshold method. The reason for larger retardation when using the continuous distribution is a small but significant sorption at locations with low zeolitic abundance. If, for practical reasons, models with homogeneous properties within each layer are used, we recommend setting nonzero K(d)s in the vitric tuffs to mimic the more rigorous continuous distribution simulations. Regions with high zeolitic abundance may not be as effective in retarding radionuclides such as Neptunium since these rocks are lower in permeability and contaminants can

  20. Characterization of unsaturated zone hydrogeologic units using matrix properties and depositional history in a complex volcanic environment

    USGS Publications Warehouse

    Flint, L.E.; Buesch, D.C.; Flint, A.L.

    2006-01-01

    Characterization of the physical and unsaturated hydrologic properties of subsurface materials is necessary to calculate flow and transport for land use practices and to evaluate subsurface processes such as perched water or lateral diversion of water, which are influenced by features such as faults, fractures, and abrupt changes in lithology. Input for numerical flow models typically includes parameters that describe hydrologic properties and the initial and boundary conditions for all materials in the unsaturated zone, such as bulk density, porosity, and particle density, saturated hydraulic conductivity, moisture-retention characteristics, and field water content. We describe an approach for systematically evaluating the site features that contribute to water flow, using physical and hydraulic data collected at the laboratory scale, to provide a representative set of physical and hydraulic parameters for numerically calculating flow of water through the materials at a site. An example case study from analyses done for the heterogeneous, layered, volcanic rocks at Yucca Mountain is presented, but the general approach for parameterization could be applied at any site where depositional processes follow deterministic patterns. Hydrogeologic units at this site were defined using (i) a database developed from 5320 rock samples collected from the coring of 23 shallow (<100 m) and 10 deep (500-1000 m) boreholes, (ii) lithostratigraphic boundaries and corresponding relations to porosity, (iii) transition zones with pronounced changes in properties over short vertical distances, (iv) characterization of the influence of mineral alteration on hydrologic properties such as permeability and moisture-retention characteristics, and (v) a statistical analysis to evaluate where boundaries should be adjusted to minimize the variance within layers. Model parameters developed in this study, and the relation of flow properties to porosity, can be used to produce detailed and

  1. Unsaturated-zone fast-path flow calculations for Yucca Mountain groundwater travel time analyses (GWTT-94)

    SciTech Connect

    Arnold, B.W.; Altman, S.J.; Robey, T.H.

    1995-08-01

    Evaluation of groundwater travel time (GWTT) is required as part of the investigation of the suitability of Yucca Mountain as a potential high-level nuclear-waste repository site. The Nuclear Regulatory Commission`s GWTT regulation is considered to be a measure of the intrinsic ability of the site to contain radionuclide releases from the repository. The work reported here is the first step in a program to provide an estimate of GWTT at the Yucca Mountain site in support of the DOE`s Technical Site Suitability and as a component of a license application. Preliminary estimation of the GWTT distribution in the unsaturated zone was accomplished using a numerical model of the physical processes of groundwater flow in the fractured, porous medium of the bedrock. Based on prior investigations of groundwater flow at the site, fractures are thought to provide the fastest paths for groundwater flow; conditions that lead to flow in fractures were investigated and simulated. Uncertainty in the geologic interpretation of Yucca Mountain was incorporated through the use of geostatistical simulations, while variability of hydrogeologic parameters within each unit was accounted for by the random sampling of parameter probability density functions. The composite-porosity formulation of groundwater flow was employed to simulate flow in both the matrix and fracture domains. In this conceptualization, the occurrence of locally saturated conditions within the unsaturated zone is responsible for the initiation of fast-path flow through fractures. The results of the GWTT-94 study show that heterogeneity in the hydraulic properties of the model domain is an important factor in simulating local regions of high groundwater saturation. Capillary-pressure conditions at the surface boundary influence the extent of the local saturation simulated.

  2. Evaluation of a horizontal permeable reactive barrier for preventing upward diffusion of volatile organic compounds through the unsaturated zone.

    PubMed

    Mahmoodlu, Mojtaba G; Hassanizadeh, S Majid; Hartog, Niels; Raoof, Amir; van Genuchten, Martinus Th

    2015-11-01

    Permeable reactive barriers are commonly used to treat contaminant plumes in the saturated zone. However, no known applications of horizontal permeable reactive barriers (HPRBs) exist for oxidizing volatile organic compounds (VOCs) in the unsaturated zone. In this study, laboratory column experiments were carried out to investigate the ability of a HPRB containing solid potassium permanganate, to oxidize the vapors of trichloroethylene (TCE), toluene, and ethanol migrating upward from a contaminated saturated zone. Results revealed that an increase in initial water saturation and HPRB thickness strongly affected the removal efficiency of the HPRB. Installing the HPRB relatively close to the water table was more effective due to the high background water content and enhanced diffusion of protons and/or hydroxides away from the HPRB. Inserting the HPRB far above the water table caused rapid changes in pH within the HPRB, leading to lower oxidation rates. The pH effects were included in a reactive transport model, which successfully simulated the TCE and toluene experimental observations. Simulations for ethanol were not affected by pH due to condensation of water during ethanol oxidation, which caused some dilution in the HRPB. PMID:26321530

  3. PRZM-3, A MODEL FOR PREDICTING PESTICIDE AND NITROGEN FATE IN THE CROP ROOT AND UNSATURATED SOIL ZONES: USER'S MANUAL FOR RELEASE 3.12.2

    EPA Science Inventory

    This publication contains documentation for the PRZM-3 model. PRZM-3 is the most recent version of a modeling system that links two subordinate models, PRZM and VADOFT, in order to predict pesticide transport and transformation down through the crop root and unsaturated soil zone...

  4. Annual report on monitoring of the unsaturated zone and recharge areas at INEL to the state of Idaho INEL Oversight Committee

    SciTech Connect

    King, B.; Bloomsburg, G.; Horn, D.; Liou, J.; Finnie, J.

    1992-01-01

    During the early years of the INEL, the USGS conducted extensive studies (sitewide drilling program) of the geology and hydrology of the area collecting varied data over the years. The unsaturated zone has not received much attention until recently. The studies that have been done are a result of problems or concerns arising from liquid radioactive waste disposal. The TRA facility has the most information published about its waste disposal activities. The ICPP has less data about the unsaturated zone due to the fact that most waste water disposal has been to a well. Little is known about the effect of waste water disposal at the NRF on the unsaturated zone. Essentially no information was found about waste disposal activities at other facilities, primarily because there does not appear to be any reported problems associated with waste water disposal at these locations. The RWMC has received much attention in the last few years as the result of being priority No. 1 in the superfund clean up of the INEL. A considerable amount of data are available describing the unsaturated zone at the RWMC. These data have been collected to field calibrate a radionuclide migration model for the RWMC.

  5. Annual report on monitoring of the unsaturated zone and recharge areas at INEL to the state of Idaho INEL Oversight Committee

    SciTech Connect

    King, B.; Bloomsburg, G.; Horn, D.; Liou, J.; Finnie, J.

    1992-12-31

    During the early years of the INEL, the USGS conducted extensive studies (sitewide drilling program) of the geology and hydrology of the area collecting varied data over the years. The unsaturated zone has not received much attention until recently. The studies that have been done are a result of problems or concerns arising from liquid radioactive waste disposal. The TRA facility has the most information published about its waste disposal activities. The ICPP has less data about the unsaturated zone due to the fact that most waste water disposal has been to a well. Little is known about the effect of waste water disposal at the NRF on the unsaturated zone. Essentially no information was found about waste disposal activities at other facilities, primarily because there does not appear to be any reported problems associated with waste water disposal at these locations. The RWMC has received much attention in the last few years as the result of being priority No. 1 in the superfund clean up of the INEL. A considerable amount of data are available describing the unsaturated zone at the RWMC. These data have been collected to field calibrate a radionuclide migration model for the RWMC.

  6. Experimental Evaluation of Gas-Phase Transport and Reactivity of Two Organophosphate Compounds in Unsaturated Porous Media

    NASA Astrophysics Data System (ADS)

    Rockhold, M.; Johnson, T.; Szecsody, J.; McKinley, J.; Blake, T.; Wietsma, T.; Covert, M.; Oostrom, M.

    2008-12-01

    An experimental study was undertaken to evaluate the feasibility of using organophosphate compounds that can be transported in the gas phase as a source of phosphorus for mineral formation (e.g. apatite) and contaminant sequestration in deep unsaturated zones. Previous work by others with gaseous phosphate compounds utilized triethyl phosphate (TEP) for bioremediation. In the current study we used both TEP and another chemically similar compound, dimethyl methylphosphonate (DMMP) that has a higher saturation vapor pressure. Batch abiotic degradation experiments in aqueous solutions with and without sediment (in both oxic and reducing conditions) indicate that both TEP and DMMP are very recalcitrant. Slow conversion from organic-to inorganic-P forms occurred (<5% in 3 months) under high temperature (80° C) and highly alkaline pH conditions. TEP and DMMP biodegradation to PO4 was found to be minimal over a similar time period using concentrated solutions of in situ microbes with no other growth substrates present. Gas transport studies using FTIR spectroscopy show that these compounds also adsorb very strongly to unsaturated sediments from the Hanford Site, to the extent that no breakthrough was observed even after >1000 pore volumes of gas exchange and complete dessication of the sediments. Methanol production was observed during the gas transport experiments, indicating that the lack of observed breakthrough of the original organophosphate compounds was attributable to both adsorption and reaction processes. FTIR reflection spectroscopy and microprobe analyses were performed to identify and quantify adsorbed species and possible mineral formation.

  7. Geohydrology of the unsaturated zone at the burial site for low-level radioactive waste near Beatty, Nye County, Nevada

    USGS Publications Warehouse

    Nichols, William D.

    1987-01-01

    Low-level radioactive solid waste has been buried in trenches at a site near Beatty, Nev., since 1962. In 1976, as part of a national program, the U.S. Geological Survey began a study of the geohydrology of the waste-burial site to provide a basis for estimating the potential for radionuclide migration in the unsaturated zone beneath the waste-burial trenches. Data collected include meteorological information for calibration of a long-term water-budget analysis, soil-moisture profiles, soil-water potentials, and hydraulic properties of representative unsaturated sediment samples to a depth of about 10 meters (m). The waste-burial facility is in the northern Amargosa Desert about 170 kilometers (km) northwest of Las Vegas, Nevo The region is arid; mean annual precipitation at Lathrop Wells, 30 km south of the site, is only 7.4 centimeters (cm). The mean daily maximum temperature at Lathrop Wells in July, the hottest month, is 37 ?C. The site is underlain by poorly stratified deposits of gravelly or silty sand and sandy gravel, and thick beds of clayey sediments. The total thickness of valley-fill deposits beneath the site is about 175 m; the unsaturated zone is about 85 m thick. Volumetric soil moisture to depths of 4 m ranges from 4 to 10 percent but commonly is in the range of 6 to 8 percent. Soil-water potential, measured to depths of 3 to 10 m, ranged from -10 to -70 bars. Unsaturated hydraulic conductivity computed from laboratory analyses of representative samples ranges from 10 -13 to 10 -14 centimeters per day (cm/d). Evaporation studies over a 2-year (yr) period were used to calibrate a numerical procedure for analyzing long-term precipitation data and estimating annual water budgets during the 15-yr period 1962-76. This analysis (1) demonstrated that a potential exists for deep percolation (greater than 2 m), despite high annual evaporation demands, and (2) provided predictions of the time of year and the antecedent conditions that enhance the probability

  8. Hydro-geophysical observations integration in numerical model: case study in Mediterranean karstic unsaturated zone (Larzac, france)

    NASA Astrophysics Data System (ADS)

    Champollion, Cédric; Fores, Benjamin; Le Moigne, Nicolas; Chéry, Jean

    2016-04-01

    Karstic hydro-systems are highly non-linear and heterogeneous but one of the main water resource in the Mediterranean area. Neither local measurements in boreholes or analysis at the spring can take into account the variability of the water storage. Since a few years, ground-based geophysical measurements (such as gravity, electrical resistivity or seismological data) allows following water storage in heterogeneous hydrosystems at an intermediate scale between boreholes and basin. Behind classical rigorous monitoring, the integration of geophysical data in hydrological numerical models in needed for both processes interpretation and quantification. Since a few years, a karstic geophysical observatory (GEK: Géodésie de l'Environnement Karstique, OSU OREME, SNO H+) has been setup in the Mediterranean area in the south of France. The observatory is surrounding more than 250m karstified dolomite, with an unsaturated zone of ~150m thickness. At the observatory water level in boreholes, evapotranspiration and rainfall are classical hydro-meteorological observations completed by continuous gravity, resistivity and seismological measurements. The main objective of the study is the modelling of the whole observation dataset by explicit unsaturated numerical model in one dimension. Hydrus software is used for the explicit modelling of the water storage and transfer and links the different observations (geophysics, water level, evapotranspiration) with the water saturation. Unknown hydrological parameters (permeability, porosity) are retrieved from stochastic inversions. The scale of investigation of the different observations are discussed thank to the modelling results. A sensibility study of the measurements against the model is done and key hydro-geological processes of the site are presented.

  9. An approximate solution for one-dimensional absorption in unsaturated porous media

    NASA Astrophysics Data System (ADS)

    Zimmerman, Robert W.; Bodvarsson, Gudmundur S.

    1989-06-01

    The "boundary layer" or "integral" method is used to derive a closed-form approximate solution for one-dimensional absorption of water in an unsaturated porous medium whose characteristic curves are of the van Genuchten type. In this approach, an assumed saturation profile is substituted into the governing equation, and integrated from the boundary out to the wetting front. This yields closed-form solutions for the front location and the instantaneous liquid flux at the boundary. The accuracy of this solution in predicting the flux, as determined by comparison with numerical solutions utilizing a Boltzmann-type transformation, is always within 15%, for any value of the initial saturation. As an example of the use of this approximate solution, saturation profiles are calculated for absorption into the Topopah Spring volcanic tuff at Yucca Mountain, Nevada, the site of the proposed nuclear waste repository.

  10. Coordinatively Unsaturated Lanthanide(III) Helicates: Luminescence Sensors for Adenosine Monophosphate in Aqueous Media.

    PubMed

    Sahoo, Jashobanta; Arunachalam, Rajendran; Subramanian, Palani S; Suresh, Eringathodi; Valkonen, Arto; Rissanen, Kari; Albrecht, Markus

    2016-08-01

    Coordinatively unsaturated double-stranded helicates [(H2 L)2 Eu2 (NO3 )2 (H2 O)4 ](NO3 )4 , [(H2 L)2 Tb2 (H2 O)6 ](NO3 )6 , and [(H2 L)2 Tb2 (H2 O)6 ]Cl6 (H2 L=butanedioicacid-1,4-bis[2-(2-pyridinylmethylene)hydrazide]) are easily obtained by self-assembly from the ligand and the corresponding lanthanide(III) salts. The complexes are characterized by X-ray crystallography showing the helical arrangement of the ligands. Co-ligands at the metal ions can be easily substituted by appropriate anions. A specific luminescence response of AMP in presence of ADP, ATP, and other anions is observed. Specificity is assigned to the perfect size match of AMP to bridge the two metal centers and to replace quenching co-ligands in the coordination sphere. PMID:27346062

  11. The multiplicity of flow and transport models in unsaturated zone – curse or blessing

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Many conceptually different models have been developed to simulate flow and transport in vadose zone. For practical purposes, parameters in these models are often estimated from readily available data using pedotransfer functions. Many pedotransfer functions have been developed, and it is not known ...

  12. Minerals in fractures of the unsaturated zone from drill core USW G-4, Yucca Mountain, Nye County, Nevada

    SciTech Connect

    Carlos, B.A.

    1985-05-01

    The mineralogy of fractures in drill core USW G-4, from a depth of nearly 800 ft to the static water level (SWL) at 1770 ft, was examined to determine the sequence of deposition and the identity of minerals that might be natural barriers to radionuclide migration from a nuclear waste repository. Mordenite was found to be present, though not abundant, at the top of the interval sampled (the top of the lower lithophysal zone of the Topopah Spring Member of the Paintbrush Tuff). Heulandite occurs from about 1245 to 1378 ft; below 1378 ft, clinoptilolite rather than heulandite occurs alone or with mordenite. Smectite in fractures is abundant only in the vitrophyre of the Topopah Spring Member of the Paintbrush Tuff and at the top of the Prow Pass member of the Crater Flat Tuff. The unsaturated zone below 800 ft can be divided into three rock types: devitrified, glassy, and zeolitized host rock. Fracture-lining zeolites for each of these three rock types differ in mineralogy and morphology. Similarities, between fracture mineralogy and host-rock alteration in the nonwelded zeolitic units of the Topopah Spring Member suggest that this zone was once below the water table. The difference between microcrystalline ({ge}.01 mm) fracture coatings in the vitric zone and the mostly cryptocrystalline (<<0.01 mm) fracture coatings in the zeolitic zone also suggests that the conditions under which these two types of linings formed were different. Nonwelded glass shards preserved in the host rock above the zeolite-mineral transition in the fractures indicate that the water table was never higher than the lithic-rich base of the Topopah Spring Member in the vicinity of USW G-4. Fracture linings in the zeolitic Topopah Spring Member are clinoptilolite, but the crystal size (0.01 to 0.02 mm) is closer to that of heulandite in fractures of the vitric zone above it than to clinoptilolite in the Tuff of Calico Hills below. 21 refs., 48 figs., 2 tabs.

  13. Transport and degradation of propyleneglycol and potassium acetate in the unsaturated zone.

    PubMed

    French, H K; Van der Zee, S E; Leijnse, A

    2001-05-01

    De-icing chemicals used during the winter season are potential pollutants for the groundwater underneath the new main airport of Norway. Several field experiments examining the transport and degradation of propyleneglycol (PG), potassium acetate (KAc) and non-reactive tracers were performed in a lysimeter trench under natural snowmelting conditions. Chemicals were applied underneath the snow cover and the transport in a heterogeneous coarse sandy soil was examined by extracting soil water from 30 or 40 suction cups placed at five depths between 0.4 and 2.4 m depth. Transport and degradation was analysed by spatial moment calculations. The de-icing chemicals showed the same basic displacement as chemically inactive tracers, an initial fast transport during the melting period followed by a period of stagnation throughout the summer season. PG seemed to be displaced to greater depths compared to non-reactive tracer after the first application. However, computer simulations of transport and degradation in a heterogeneous unsaturated soil showed that decreasing degradation constants with depth can generate a downward movement of the centre of mass without any flow occurring in the system. Potassium acetate showed some adsorption, with calculated retardation factors of approximately 1.3 and 1.2. The degradation rate constant for PG was calculated to be 0.015 day-1 in 1994 and increased to 0.047 day-1 in the second application made in 1995. The degradation rate constant for acetate was estimated to be 0.02 day-1. Increased manganese concentrations seem to be a good indicator of degradation of PG and Ac. PMID:11351514

  14. 1DFEMWATER: A one-dimensional finite element model of WATER flow through saturated-unsaturated media

    SciTech Connect

    Yeh, G.T.

    1988-08-01

    This report presents the development and verification of a one- dimensional finite element model of water flow through saturated- unsaturated media. 1DFEMWATER is very flexible and capable of modeling a wide range of real-world problems. The model is designed to (1) treat heterogeneous media consisting of many geologic formations; (2) consider distributed and point sources/sinks that are spatially and temporally variable; (3) accept prescribed initial conditions or obtain them from steady state simulations; (4) deal with transient heads distributed over the Dirichlet boundary; (5) handle time-dependent fluxes caused by pressure gradient on the Neumann boundary; (6) treat time-dependent total fluxes (i.e., the sum of gravitational fluxes and pressure-gradient fluxes) on the Cauchy boundary; (7) automatically determine variable boundary conditions of evaporation, infiltration, or seepage on the soil-air interface; (8) provide two options for treating the mass matrix (consistent and lumping); (9) provide three alternatives for approximating the time derivative term (Crank-Nicolson central difference, backward difference, and mid-difference); (10) give three options (exact relaxation, underrelaxation, and overrelaxation) for estimating the nonlinear matrix; (11) automatically reset the time step size when boundary conditions or source/sinks change abruptly; and (12) check mass balance over the entire region for every time step. The model is verified with analytical solutions and other numerical models for three examples.

  15. Compilation of an integrated 3D soil and agrogeological database for the hydrophysical characterization of the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Bakacsi, Zsófia; Kuti, László; Pásztor, László; Vatai, József; Szabó, József; Müller, Tamás.

    2010-05-01

    Describing the water movement in the unsaturated zone, numerous soil hydraulic data as input parameter are required concerning the water retention curve and the hydraulic conductivity function as the main hydraulic properties. The direct measurements of the hydraulic parameters are quite difficult and time-consuming; the estimation of them can be an alternative especially for large areas. The most commonly used basis of the estimation is the particle-size distribution (PSD) data or texture class. The aim of our work was to compile an integrated and harmonized 3D pedo- and agrogeological database with the physical properties and stratification of the formations to the depth of the permanent groundwater level, which describes the unsaturated zone in a 690 km2 pilot area. Since the existing pedo- and agrogeological databases are not able to serve separately these 3D model requirements, their integration was necessary. Due to its appropriate spatial and thematic resolution and data processing status, the Digital Kreybig Soil Information System (DKSIS) was chosen as pedological data source of the 3D model. The DKSIS has been compiled in the Research Institute for Soil Science and Agricultural Chemistry of the Hungarian Academy of Sciences, based on the 1:25,000 scale, national soil mapping program in Hungary. The survey sheets indicate the location of the observation sites. Due to the lack of measured PSD data, the field estimation of the textural classes, and the so-called "capillary rise of water" were used for the definition of the texture classes. The measured water uptake is supposed to have good relation with the textural class of the sample. During the data processing the inconsistent fields vs. capillary data pairs were excluded. In the DKSIS 649 polygons cover the pilot area, 484 soil profiles are occurring and characteristically each profile has two or three horizons. The agrogeological dataset is maintained by the Hungarian Geological Institute and derives

  16. Road Salt Accumulation in Highway Snow Banks and Transport Through the Unsaturated Zone of the Oak Ridges Moraine, Southern Ontario

    NASA Astrophysics Data System (ADS)

    Labadia, C. F.; Buttle, J. M.

    1996-12-01

    Pathways and fate of road deicing salt (NaCl) applied during the 1994-1995 winter were studied for a 14-km section of a major highway that crosses the Oak Ridges Moraine in southern Ontario. Total salt applications over the winter ranged from 29 to 74 kg m-1 of highway, and NaCl concentrations in snow banks adjacent to the roadway reached 9400 mg l-1 during the later stages of snow cover development. This salt was released to the ground surface during snowmelt. Sodium chloride (NaCl) loadings to soil from snow cover during the final melt phase were relatively uniform along the study section (3-5 kg NaCl m-1 of highway). However, the snowpack at all transects retained <50% of applied NaCl, and this shortfall probably reflected direct runoff and infiltration of saline meltwater from the road surface into the adjacent shoulder and right-of-way. Cation exchange with Ca2+ in near-surface soils most likely resulted in preferential retention of Na+ relative to Cl-, although total storage of NaCl in upper soil horizons by winter's end was <15% of deicing salt applications. An environmental tracer (18O) was used to trace movement of saline meltwater through the unsaturated zone underlying the highway. Average meltwater particle velocities at a site underlain by loam soils were 0.02 m d-1, and ca. 280 mm of water was displaced below a depth of 1.86 m over a 78-day period in the spring and summer of 1995. Sodium ion and chloride ion concentrations in water sampled in late summer 1995 at depths >2 m exceeded 500 mg l-1 and 1000 mg l-1, respectively. Approximately 75% of the net flux of NaCl below the upper soil was retained in the 0-2.8 m depth interval at this site, and results from more permeable soils traversed by the highway indicate an even greater penetration of the annual NaCl application into the unsaturated zone along the moraine. This saline water likely recharges groundwater in this portion of the Oak Ridges Moraine.

  17. Land-Use Change in Arid Regions Can Mobilize Millennial Accumulations of Unsaturated-Zone Salts

    NASA Astrophysics Data System (ADS)

    Stonestrom, D. A.; Prudic, D. E.; Walvoord, M. A.; Jackson, W.

    2005-12-01

    Studies from arid regions around the world have reported elevated pore-water concentrations of chloride just beneath the root zones of xeric vegetation. Recent work in the Amargosa Desert shows that these chloride "bulges" are accompanied by accumulations of other salts, including nitrate, sulfate, and perchlorate. Several lines of evidence indicate that atmospherically deposited salts have been accumulating beneath the root zones of interfluvial desert vegetation in the western United States since at least the end of the Pleistocene, when wetter and cooler conditions gave way to the hot and dry conditions of today. Transport simulations and chloride mass-balance calculations suggest that thousands of years of negligible deep percolation are required to accumulate the observed sub-root salt accumulations. Salt bulges are absent beneath a long-established, incised reach of the ephemeral Amargosa River in southwestern Nevada but are present, though translocated downwards, beneath a non-incised reach that was established during historic flood-induced channel migration in 1969. Desert areas that were converted from native vegetation to irrigated agriculture have salt bulges that have been translocated downward by deeply percolating irrigation water. Downward translocations of bulges indicate that accumulated nitrate and other salts can be rapidly transported to ground water once recharging conditions are established. Travel-velocity estimates of deep water fluxes agree approximately with chloride mass-balance estimates, supporting the idea of quick release of accumulated salts. Estimated fluxes range from 0.02 to 0.5 m/yr. Given modern conversion of large desert areas to agriculture, irrigation-triggered release of sub-root zone accumulations may account for previously unexplained contamination of water-table aquifers with nitrate, perchlorate, and other atmospherically deposited salts.

  18. Water composition in the unsaturated zone at Sete Cidades central volcano (S. Miguel, Azores, Portugal)

    NASA Astrophysics Data System (ADS)

    Cruz, J.; Silva, M.; Mendonça, J.; Dias, I.; Prudêncio, I.

    2009-04-01

    A field study was developed at Sete Cidades, the westernmost of the three active composite volcanoes that dominate the geology of São Miguel, the largest of the nine islands from the Azores archipelago. Research methodology comprehends the characterization of soil-water composition at several depths, sampled by means of ceramic suction cups. Previously to their installation, cups were all submitted to several stages of washing, first in the laboratory with supra pure water, until aliquot conductivity stabilizes, and after in the field. This study was planned in order to study the water pollution due to agriculture, one of the main economic activities in the Azores, as shown by the gross value added to regional product. The negative effects of groundwater pollution due to agriculture have been reported in the majority of the nine islands, reflected by high contents of nitrogen species, derived from the inadequate use of synthetic and organic fertilizers, as well as from animal wastes leaching, or also by microbiology parameters. The relation between water pollution and agriculture results in some cases in the failure to comply regarding EU and national water quality regulations, through quality deterioration and compromising groundwater as strategic natural resource in the Azores. The studied area corresponds to Sete Cidades volcano caldera, a 5 km-diameter circular shaped depression, contoured by steep walls from 30 m high up to 400 m. In order to characterize unsaturated water composition in the caldera floor, five pasture locations were selected and monitored, as well as one site with the same physical conditions, but without agricultural activity. From the 5 pasture lands we discuss further results obtained in the so-called Pavão I (Pa I), which corresponds to the most extensive data set. On this site, 6 suction cups were installed, at depths 0.35 m, 0.7 m, 1 m, 1.3 m, 1.6 m and 1.9 m. In the site without agricultural activity, in the vicinity of Sete Cidades

  19. Pyrite oxidation in saturated and Unsaturated Porous Media Flow: AComparison of alternative mathematical modeling approaches

    SciTech Connect

    Xu, Tianfu; White, Stephen P.; Pruess, Karsten

    1998-02-15

    Pyrite (FeS{sub 2}) is one of the most common naturally occurring minerals that is present in many subsurface environments. It plays an important role in the genesis of enriched ore deposits through weathering reactions, is the most abundant sulfide mineral in many mine tailings, and is the primary source of acid drainage from mines and waste rock piles. The pyrite oxidation reaction serves as a prototype for oxidative weathering processes with broad significance for geoscientific, engineering, and environmental applications. Mathematical modeling of these processes is extremely challenging because aqueous concentrations of key species vary over an enormous range, oxygen inventory and supply are typically small in comparison to pyrite inventory, and chemical reactions are complex, involving kinetic control and microbial catalysis. We present the mathematical formulation of a general multi-phase advective-diffusive reactive transport model for redox processes. Two alternative implementations were made in the TOUGHREACT and TOUGH2-CHEM simulation codes which use sequential iteration and simultaneous solution, respectively. The simulators are applied to reactive consumption of pyrite in (1) saturated flow of oxidizing water, and (2) saturated-unsaturated flow in which oxygen transport occurs in both aqueous and gas phases. Geochemical evolutions predicted from different process models are compared, and issues of numerical accuracy and efficiency are discussed.

  20. Low-frequency dilatational wave propagation through unsaturated porous media containing two immiscible fluids

    SciTech Connect

    Lo, W.-C.; Sposito, G.; Majer, E.

    2007-02-01

    An analytical theory is presented for the low-frequency behavior of dilatational waves propagating through a homogeneous elastic porous medium containing two immiscible fluids. The theory is based on the Berryman-Thigpen-Chin (BTC) model, in which capillary pressure effects are neglected. We show that the BTC model equations in the frequency domain can be transformed, at sufficiently low frequencies, into a dissipative wave equation (telegraph equation) and a propagating wave equation in the time domain. These partial differential equations describe two independent modes of dilatational wave motion that are analogous to the Biot fast and slow compressional waves in a single-fluid system. The equations can be solved analytically under a variety of initial and boundary conditions. The stipulation of 'low frequency' underlying the derivation of our equations in the time domain is shown to require that the excitation frequency of wave motions be much smaller than a critical frequency. This frequency is shown to be the inverse of an intrinsic time scale that depends on an effective kinematic shear viscosity of the interstitial fluids and the intrinsic permeability of the porous medium. Numerical calculations indicate that the critical frequency in both unconsolidated and consolidated materials containing water and a nonaqueous phase liquid ranges typically from kHz to MHz. Thus engineering problems involving the dynamic response of an unsaturated porous medium to low excitation frequencies (e.g. seismic wave stimulation) should be accurately modeled by our equations after suitable initial and boundary conditions are imposed.

  1. Puddles - A trigger for heterogeneous chemical influx into the unsaturated zone.

    PubMed

    Zentner, Eitan; Weisbrod, Noam; Gerstl, Zev; Gasser, Guy; Ronen, Daniel

    2015-09-01

    Spatial heterogeneity in the chemical concentration of interstitial water in the vadose zone was previously observed under apparently homogeneous surface conditions on two leveled fields sprinkler irrigated with treated sewage effluents on the phreatic Coastal Plain aquifer of Israel. This phenomenon greatly hampers the monitoring of groundwater quality. In this study we report on the presence of puddles of different size and shape that were sporadically observed in these fields. Temporal variability noted in the concentration of treated sewage effluents components in the puddles were considered to be related to evapotranspiration and degradation. For example: increases in the electrical conductivity (up to 1.32 mS/cm), and in the concentrations of chloride (up to 521 mg/L), dissolved organic carbon (up to 28.4 mg/L), and carbamazepine (up to 780 ng/L) and decreases in the concentrations of nitrate (up to 20.1mg/L) and caffeine (3,396 ng/L). Variable trends in concentration were observed for sulfamethoxazole, venlafaxine, 10-hydroxy-10,11-dihydrocarbamazepine and o-desmethylvenlafaxine. The presence of puddles was not necessarily related to areas with high irrigation water input. It is postulated that the continuous chemical variability in the puddles, whose location and size are also variable, determine a heterogeneous influx of solutes into the soil and subsequently into the vadose zone. PMID:25957034

  2. Methodology for assessment of contamination of the unsaturated zone by leaking underground storage tanks

    SciTech Connect

    DiGiano, F.A.; Miller, C.T.; Roche, A.C.; Wallingford, E.D.

    1988-01-01

    Three methods of measuring contamination of the partially saturated zone by leaking underground fuel tanks were investigated. Two of the methods relied upon obtaining a soil core from the field. These differed in the method of extraction: (1) by nitrogen purge of the entire core, followed by adsorption-solvent extraction and gas chromatographic (GC) analysis, and (2) by sonication of a small sub-sample from the core, followed by solvent extraction and GC analysis. The third method focused on saturation zone. This required use of a driveable ground probe (DGP) and activated carbon trap, followed by solvent extraction and GC analysis. The soil core procedures required construction of a sampling tube that proved successful in the system upon return to the laboratory. Recoveries approaching 100% were achieved in the nitrogen purge procedure by: heating the soil core to 100 C; trapping water exiting the soil core prior to the adsorption step; and using activated carbon instead of Tenax as the adsorbent. Vapor phase measurements provided a convenient way to map the extent of contamination from a leaking underground gasoline storage tank at the Camp Lejeune site. Concentrations of target compounds ranged from 10,000 micrograms/L (ug/L) to < 10 ug/L of vapor phase. The highest concentrations were found above the non-aqueous-phase liquid (NAPL). However, the method was able to show that contamination exists well beyond the NAPL, although the concentrations drop off precipitously. 36 refs., 29 figs., 11 tabs.

  3. Modeling study of solute transport in the unsaturated zone: Workshop proceedings

    SciTech Connect

    Springer, E.P.; Fuentes, H.R.

    1987-04-01

    Issues addressed were the adequacy of the data for the various models, effectiveness of the models to represent the data, particular information provided by the models, the role of caisson experiments in providing fundamental knowledge of porous-media water flow and solute transport, and the importance of geochemistry to the transport of nonconservative tracers. These proceedings include the presentations made by each of the modelers; the summary document written by the panel; and a transcript of the discussions, both the discussions that followed individual presentations and the general discussion held on the second day. This publication completes the series on the workshop. Volume I in the series (NUREG/CR-4615, Vol. I) contains background information and the data sets provided each modeler.

  4. FEMWASTE: a Finite-Element Model of Waste transport through porous saturated-unsaturated media

    SciTech Connect

    Yeh, G.T.; Ward, D.S.

    1981-04-01

    A two-dimensional transient model for the transport of dissolved constituents through porous media originally developed at Oak Ridge National Laboratory (ORNL) has been expanded and modified. Transport mechanisms include: convection, hydrodynamic dispersion, chemical sorption, and first-order decay. Implementation of quadrilateral iso-parametric finite elements, bilinear spatial interpolation, asymmetric weighting functions, several time-marching techniques, and Gaussian elimination are employed in the numerical formulation. A comparative example is included to demonstrate the difference between the new and original models. Results from 12 alternative numerical schemes of the new model are compared. The waste transport model is compatible with the water flow model developed at ORNL for predicting convective Darcy velocities in porous media which may be partially saturated.

  5. Microbial Growth, Water Flow, and Solute Transport in Unsaturated Porous Media

    NASA Astrophysics Data System (ADS)

    Yarwood, R. R.; Rockhold, M. L.; Niemet, M. R.; Bottomley, P. J.; Selker, J. S.

    2004-05-01

    We present an investigation that studied interactions between microbial growth, water flow, and solute transport in variably saturated porous media. The experimental system provided for continuous, noninvasive observation of microbial activity, while simultaneously monitoring water content and solute flow paths in a two-dimensional porous matrix. The spatial and temporal development of microbial colonization by a Pseudomonas fluorescens bacterium was monitored by induction of a bioluminescent phenotype. A model was developed that allowed quantification of population density from bioluminescence measurements. Liquid saturation was quantified from the transmission of light through the system, and solute flow paths were determined with a dye tracer. Dramatic changes in microbial colonization were observed, including upward migration against flow. This migration was particularly interesting because it cannot be explained by passive transport. Bacterial growth and accumulation significantly impacted the hydrologic properties of the media, including apparent desaturation within the colonized region, diversion of flow around the colonized region, and lowering of the capillary fringe height.

  6. Tritium and 36Cl as constraints on fast fracture flow and percolation flux in the unsaturated zone at Yucca Mountain

    NASA Astrophysics Data System (ADS)

    Guerin, Marianne

    2001-10-01

    An analysis of tritium and 36Cl data collected at Yucca Mountain, Nevada suggests that fracture flow may occur at high velocities through the thick unsaturated zone. The mechanisms and extent of this "fast flow" in fractures at Yucca Mountain are investigated with data analysis, mixing models and several one-dimensional modeling scenarios. The model results and data analysis provide evidence substantiating the weeps model [Gauthier, J.H., Wilson, M.L., Lauffer, F.C., 1992. Proceedings of the Third Annual International High-level Radioactive Waste Management Conference, vol. 1, Las Vegas, NV. American Nuclear Society, La Grange Park, IL, pp. 891-989] and suggest that fast flow in fractures with minimal fracture-matrix interaction may comprise a substantial proportion of the total infiltration through Yucca Mountain. Mixing calculations suggest that bomb-pulse tritium measurements, in general, represent the tail end of travel times for thermonuclear-test-era (bomb-pulse) infiltration. The data analysis shows that bomb-pulse tritium and 36Cl measurements are correlated with discrete features such as horizontal fractures and areas where lateral flow may occur. The results presented here imply that fast flow in fractures may be ubiquitous at Yucca Mountain, occurring when transient infiltration (storms) generates flow in the connected fracture network.

  7. The role of porous matrix in water flow regulation within a karst unsaturated zone: an integrated hydrogeophysical approach

    NASA Astrophysics Data System (ADS)

    Carrière, Simon D.; Chalikakis, Konstantinos; Danquigny, Charles; Davi, Hendrik; Mazzilli, Naomi; Ollivier, Chloé; Emblanch, Christophe

    2016-05-01

    Some portions of the porous rock matrix in the karst unsaturated zone (UZ) can contain large volumes of water and play a major role in water flow regulation. The essential results are presented of a local-scale study conducted in 2011 and 2012 above the Low Noise Underground Laboratory (LSBB - Laboratoire Souterrain à Bas Bruit) at Rustrel, southeastern France. Previous research revealed the geological structure and water-related features of the study site and illustrated the feasibility of specific hydrogeophysical measurements. In this study, the focus is on hydrodynamics at the seasonal and event timescales. Magnetic resonance sounding (MRS) measured a high water content (more than 10 %) in a large volume of rock. This large volume of water cannot be stored in fractures and conduits within the UZ. MRS was also used to measure the seasonal variation of water stored in the karst UZ. A process-based model was developed to simulate the effect of vegetation on groundwater recharge dynamics. In addition, electrical resistivity tomography (ERT) monitoring was used to assess preferential water pathways during a rain event. This study demonstrates the major influence of water flow within the porous rock matrix on the UZ hydrogeological functioning at both the local (LSBB) and regional (Fontaine de Vaucluse) scales. By taking into account the role of the porous matrix in water flow regulation, these findings may significantly improve karst groundwater hydrodynamic modelling, exploitation, and sustainable management.

  8. Tritium and 36Cl as constraints on fast fracture flow and percolation flux in the unsaturated zone at Yucca Mountain.

    PubMed

    Guerin, M

    2001-10-01

    An analysis of tritium and 36Cl data collected at Yucca Mountain, Nevada suggests that fracture flow may occur at high velocities through the thick unsaturated zone. The mechanisms and extent of this "fast flow" in fractures at Yucca Mountain are investigated with data analysis, mixing models and several one-dimensional modeling scenarios. The model results and data analysis provide evidence substantiating the weeps model [Gauthier, J.H., Wilson, M.L., Lauffer, F.C., 1992. Proceedings of the Third Annual International High-level Radioactive Waste Management Conference, vol. 1, Las Vegas, NV. American Nuclear Society, La Grange Park, IL, pp. 891-989] and suggest that fast flow in fractures with minimal fracture-matrix interaction may comprise a substantial proportion of the total infiltration through Yucca Mountain. Mixing calculations suggest that bomb-pulse tritium measurements, in general, represent the tail end of travel times for thermonuclear-test-era (bomb-pulse) infiltration. The data analysis shows that bomb-pulse tritium and 36Cl measurements are correlated with discrete features such as horizontal fractures and areas where lateral flow may occur. The results presented here imply that fast flow in fractures may be ubiquitous at Yucca Mountain, occurring when transient infiltration (storms) generates flow in the connected fracture network. PMID:11588829

  9. Distribution and degradation of diesel oil in the unsaturated zone following an oil spill on a chalk aquifer

    NASA Astrophysics Data System (ADS)

    Ashley, R. P.; Lerner, D. N.; Lloyd, J. W.

    1994-07-01

    In 1976, there occurred a substantial loss of diesel oil from a storage facility at Royston in eastern England. The site is on the outcrop of the important Chalk aquifer, which is protected by an unsaturated zone 24-30 m thick. In 1986, a cored borehole was drilled through the site of the spillage to investigate the fate of the contaminants. The core samples were analysed by physical and chemical methods to determine the physical structure of the rock, and the characteristics and distribution of the oil. The chemically analysed samples included pore water extracts, scrapings from fracture surfaces, and non-fracture (matrix) samples. The results indicate that oil accumulated within a few millimetres of major fissure surfaces, and entry into the rock matrix was limited by the small size of pores and the presence of water. Oil may also have migrated along microscopic channels away from the major fissures. There was no evidence of downward migration of oil since the initial phase of movement. The adoption of certain assumptions regarding degradation, evaporation and dissolution processes allows the estimation of oil depletion caused by these processes. Physical weathering and degradation were found to have been extensive, but highly variable. Both processes occurred on the major fissure surfaces but, in the matrix, degradation appears to have been restricted. The conclusions have implications for the investigation and remediation of fissured Chalk aquifers contaminated by oil.

  10. Linking drainage front morphology with gaseous diffusion in unsaturated porous media: a lattice Boltzmann study.

    PubMed

    Chau, Jessica Furrer; Or, Dani

    2006-11-01

    The effect of drainage front morphology on gaseous diffusion through partially saturated porous media is analyzed using the lattice Boltzmann method (LBM). Flow regimes for immiscible displacement in porous media have been characterized as stable displacement, capillary fingering, and viscous fingering. The dominance of a flow regime is associated with the relative magnitudes of gravity, viscous, and capillary forces, quantifiable via the Bond number Bo, capillary number Ca, and their difference, Bo-Ca . Forced drainage from an initially saturated two-dimensional (2D) porous medium was simulated and the resulting flow patterns were analyzed and compared with theoretical predictions and experimental results. The LBM simulations reproduced expected flow morphologies for a range of drainage velocities and gravitational forces (i.e., a range of capillary and Bond numbers). Furthermore, measures of drainage front width as a function of the dimensionless difference Bo-Ca correspond well with scaling laws derived from percolation theory. Effects of flow morphology on residual fluid entrapment and gaseous diffusion were assessed by running LBM diffusion simulations through the partially saturated domain for a range of water contents. The effective diffusion coefficient as a function of water content was estimated for three regimes: stable drainage front, capillary fingering, and viscous fingering. Significant reductions in gaseous diffusion coefficient were found for viscous fingering relative to stable displacement, and to a lesser extent for capillary fingering, indicating that wetting phase distribution with a high degree of fingering in the 2D domain severely restricts connectivity of gas diffusion pathways through the medium. The study lends support for the use of LBM in design and management of fluids in porous media under variable gravity, and enhances the understanding of the role of dynamic fluid behavior on macroscopic transport properties of partially saturated

  11. Concentrations of triazine herbicides in the unsaturated zone in western Harvey County, Kansas, spring and fall 1992-93

    USGS Publications Warehouse

    Juracek, Kyle E.

    1994-01-01

    To assess the potential transport of triazine herbicides into the Equus Beds aquifer, soil samples were collected from the unsaturated zone at 27 dryland and 30 irrigated sites in western Harvey County, Kansas. All sites were sampled at a depth of 4 to 6 feet (that is, immediately below the root zone) during March and October-November 1992 and March and October-November 1993. During the October-November 1992 and March 1993 sampling periods, five sites also were sampled at depths of 0 to 4 and 6 to 10 feet. All samples were analyzed for total triazine concentrations using a 20-gram extraction, immunoassay technique with a 0.02 microgram per kilogram detection level. Additionally, 20 samples from each sampling period were analyzed specifically for atrazine and two atrazine metabolites (deethylatrazine and deisopropylatrazine) using a 20-gram extraction, gas chromatography/mass spectrometry procedure with a 0.5 microgram per kilogram detection level. Total triazine concentrations at the 4- to 6-foot depth, with one exception, were less than 1.0 microgram per kilogram, with the majority of the concen- trations less than 0.10 microgram per kilogram. Triazine concentrations at the O- to 4-foot depth ranged from 0.51 to 12.20 micrograms per kilogram. Triazine concentrations at the 6- to 10-foot depth ranged from less than 0.02 to 0.33 microgram per kilogram. The atrazine metabolite deethylatrazine was detected in three samples, with concentrations of 0.63, 1.44, and 1.48 micrograms per kilogram. The atrazine metabolite deisopropylatrazine was not detected in any of the soil samples analyzed. Because the 1992 and 1993 growing seasons included periods of above-normal rainfall, the concentrations of triazine herbicides and metabolites measured during this study may not be indicative of average conditions.

  12. Tritium Plume Dynamics in the Shallow Unsaturated Zone Adjacent to an Arid Waste Disposal Facility

    NASA Astrophysics Data System (ADS)

    Maples, S.; Andraski, B. J.; Stonestrom, D. A.; Cooper, C. A.; Michel, R. L.; Pohll, G. M.

    2012-12-01

    Previous studies at the U.S. Geological Survey's Amargosa Desert Research Site (ADRS) in southern Nevada have documented two plumes of tritiated water-vapor (3HHOg) adjacent to a closed, commercial low-level radioactive waste disposal facility. Wastes were disposed on-site from 1962-92. Tritium has moved long distances (> 400 m) through a shallow (1-2-m depth) dry gravelly layer—orders of magnitude further than anticipated by standard transport models. Geostatistical methods, spatial moment analyses and tritium flux calculations were applied to assess shallow plume dynamics. A grid-based plant-water sampling method was utilized to infer detailed, field-scale 3HHOg concentrations at 5-yr intervals during 2001-11. Results indicate that gravel-layer 3HHOg mass diminished faster than would be expected from radioactive decay (~70% in 10 yr). Both plumes exhibited center-of-mass stability, suggesting that bulk-plume movement is minimal during the period of study. Nonetheless, evidence of localized lateral advancement along some margins, combined with increases in the spatial covariance of concentration distribution, indicates intra-plume mass redistribution is ongoing. Previous studies have recognized that vertical movement of tritiated water from sub-root-zone gravel into the root-zone contributes to atmospheric release via evapotranspiration. Estimates of lateral and vertical tritium fluxes during the study period indicate (1) vertical tritiated water fluxes were dominated by diffusive-vapor fluxes (> 90%), and (2) vertical diffusive-vapor fluxes were roughly an order of magnitude greater than lateral diffusive-vapor fluxes. This behavior highlights the importance of the atmosphere as a tritium sink. Estimates of cumulative vertical diffusive-vapor flux and radioactive decay with time were comparable to observed declines in total shallow plume mass with time. This suggests observed changes in plume mass may (1) be attributed, in considerable part, to these removal

  13. Vertical Distribution of Calcite at Yucca Mountain, Nevada, as an Indicator of Flow Through a Thick Unsaturated Zone

    SciTech Connect

    J.B. Paces; Z.E. Peterman

    2001-07-20

    Meteoric water percolating through 500 to 700 m of hydrologically unsaturated felsic tuffs provides a mechanism for release and transport of radionuclides from a potential high-level radioactive waste repository at Yucca Mountain, Nevada. Modern flow through the unsaturated zone (UZ) is low (probably <20 mm/year) and has not been observed directly. However, calcite formed from water percolating through fracture and lithophysal cavities over the last 12.8 million years provides, in part, a time-integrated record of UZ flow. Calcite concentration profiles were determined in dry-drilled boreholes USW WT-24 and USW SD-6 by acidifying samples of powdered rock cuttings collected over 5-foot intervals and measuring the evolved CO{sub 2} using gas chromatography. Resulting CO{sub 2}-derived calcite concentrations ranged from 30,800 to less than 20 ppm. Aliquots of the same powders also were analyzed for Ca, Ti, and Zr by energy-dispersive X-ray fluorescence. Concentrations of Ti and Zr in the crystal-poor, high-silica rhyolite parts of the Topopah Spring Tuff are uniform (standard deviations of 3 to 4%); however, Ca scatters widely (standard deviations of 21 and 32%). Concentrations of Ca are positively correlated to CO{sub 2}-derived calcite concentrations and regressions for samples of the two major rhyolitic tuffs yielded r{sup 2} values >0.9, CO{sub 2}-intercept Ca concentrations in the range of values determined on fresh rock samples, and slopes equivalent to addition of stoichiometric calcite. Therefore, combined CO{sub 2} and Ca data provide a means of determining the amount of secondary calcite added to the rock mass from percolating water. The vertical distribution of calcite is related to lithostratigraphy with the largest concentrations in the welded hydrogeologic unit of the Tiva Canyon Tuff near the land surface and progressively smaller values with depth into the underlying nonwelded units. Large values also may be present in the upper parts of the underlying

  14. Quantification of unsaturated-zone alteration and cation exchange in zeolitized tuffs at Yucca Mountain, Nevada, USA

    NASA Astrophysics Data System (ADS)

    Vaniman, David T.; Chipera, Steve J.; Bish, David L.; Carey, J. William; Levy, Schön S.

    2001-10-01

    Zeolitized horizons in the unsaturated zone (UZ) at Yucca Mountain, Nevada, USA, are an important component in concepts for a high-level nuclear waste repository at this site. The use of combined quantitative X-ray diffraction and geochemical analysis allows measurement of the chemical changes that accompanied open-system zeolitization at Yucca Mountain. This approach also provides measures of the extent of chemical migration that has occurred in these horizons as a result of subsequent cation exchange. Mass-balance analysis of zeolitized horizons with extensive cation exchange (drill hole UZ-16) and with only minimal cation exchange (drill hole SD-9) shows that Al is essentially immobile. Although zeolitization occurred in an open system, the mass transfer of constituents other than water is relatively small in initial zeolitization, in contrast to the larger scales of cation exchange that can occur after zeolites have formed. Cation exchange in the clinoptilolite ± mordenite zeolitized horizons is seen in downward-diminishing concentration gradients of Ca, Mg, and Sr exchanged for Na and (to lesser extent) K. Comparison with data from drill hole SD-7, which has multiple zeolitized horizons above the water table, shows that the upper horizons accumulate Ca, Mg, and Sr to such an extent that transport of these elements to the deepest UZ zeolitized horizon can be blocked. Quantitative analysis of zeolite formation yields insight into processes that are implied from laboratory studies and modeling efforts but are otherwise unverified at the site. Such analysis also yields information not provided by or contradicted by some models of flow and transport. The results include the following: (1) evidence of effective downward flow through zeolitic horizons despite the low permeability of these horizons, (2) evidence that alkaline-earth elements accumulated by zeolites are mostly derived from eolian materials in surface soils, (3) validation of the very effective

  15. An Approach Using Gas Monitoring to Find the Residual TCE Location in the Unsaturated Zone of Woosan Industrial Complex (WIC), Korea

    NASA Astrophysics Data System (ADS)

    Koh, Y.; Lee, S.; Yang, J.; Lee, K.

    2012-12-01

    An area accommodating various industrial facilities has fairly high probability of groundwater contamination with multiple chlorinated solvents such as trichloroethene (TCE), carbon tetrachloride (CT), and chloroform (CF). Source tracing of chlorinated solvents in the unsaturated zone is an essential procedure for the management and remediation of contaminated area. From the previous study on seasonal variations in hydrological stresses and spatial variations in geologic conditions on a TCE plume, the existence of residual DNAPLs at or above the water table has proved. Since TCE is one of the frequently detected VOCs (Volatile Organic Compounds) in groundwater, residual TCE can be detected by gas monitoring. Therefore, monitoring of temporal and spatial variations in the gas phase TCE contaminant at an industrial complex in Wonju, Korea, were used to find the residual TCE locations. As pilot tests, TCE gas samples collected in the unsaturated zone at 4 different wells were analyzed using SPME (Solid Phase MicroExtraction) fiber and Gas Chromatography (GC). The results indicated that detecting TCE in gas phase was successful from these wells and TCE analysis on gas samples, collected from the unsaturated zone, will be useful for source area characterization. However, some values were too high to doubt the accuracy of the current method, which needs a preliminary lab test with known concentrations. The modified experiment setups using packer at different depths are in process to find residual TCE locations in the unsaturated zone. Meanwhile, several PVD (polyethylene-membrane Passive Vapor Diffusion) samplers were placed under water table to detect VOCs by equilibrium between air in the vial and VOCs in pore water.

  16. Influence of The Physico-chemical Factors On The Transport of Colloids Through Saturated and Unsaturated Porous Media

    NASA Astrophysics Data System (ADS)

    Solovitch, N.; Garnier, J. M.

    attributed to the desorption from "rapid" sorption sites while tailing indicated the desorption from "slow" sorption sites. With regard to unsaturated media, the retention of colloids was greater than for saturated media. The behavior of the colloids is important for understanding of the mechanisms of radionuclides migration in soils.

  17. Effect of Viscous Cross Coupling between two Immiscible Fluids on Elastic Wave Propagation and Attenuation in Unsaturated Porous Media

    NASA Astrophysics Data System (ADS)

    Lo, WeiCheng; Lee, JheWei; Lee, ChengHaw

    2015-04-01

    A central issue in the theoretical treatment of a multiphase system is the proper mathematical description of momentum transfer across fluid-solid and fluid-fluid interfaces. Although recent studies have advanced our knowledge on modeling the coupling behavior between a porous framework and the fluids permeating it, the effect of viscous resistance caused by two-fluid flow on elastic wave behavior in unsaturated porous media still remains unaddressed. In the present study, we generalize the theory of dynamic poroelasticity to incorporate viscous cross coupling arising from the velocity difference between two adjacent fluids for examining the dynamic behavior of fluid flow in deformable porous media related to harmonic wave perturbation. The corresponding dispersion relations that characterize three compressional waves and one shear wave are precisely formulated, with the coefficients featuring all elasticity, inertial coupling, and viscous coupling parameters, for describing how wave number changes as excitation frequency is stipulated. To evaluate quantitatively this as-yet unknown effect, numerical simulations are implemented to solve the dispersion relations for Columbia fine sandy loam bearing an oil-water mixture with respect to three representative wave excitation frequencies. Our results show that the phase speed and attenuation coefficient of the third compressional wave which has the smallest speed is strongly sensitive to the presence of viscous cross coupling, as expected for this wave being attributed primarily to the out-of-phase motion of the two pore fluids. Viscous cross coupling also exerts an impact on the attenuation coefficient of the shear wave and the first compressional wave whose speed is greatest, which exhibits two opposite trends at different ranges of low and high water contents. A sensitivity analysis is further conducted to provide information on the importance of the coupling parameter, revealing that the effect becomes more

  18. User`s Guide: Database of literature pertaining to the unsaturated zone and surface water-ground water interactions at the Idaho National Engineering Laboratory

    SciTech Connect

    Hall, L.F.

    1993-05-01

    Since its beginnings in 1949, hydrogeologic investigations at the Idaho National Engineering Laboratory (INEL) have resulted in an extensive collection of technical publications providing information concerning ground water hydraulics and contaminant transport within the unsaturated zone. Funding has been provided by the Department of Energy through the Department of Energy Idaho Field Office in a grant to compile an INEL-wide summary of unsaturated zone studies based on a literature search. University of Idaho researchers are conducting a review of technical documents produced at or pertaining to the INEL, which present or discuss processes in the unsaturated zone and surface water-ground water interactions. Results of this review are being compiled as an electronic database. Fields are available in this database for document title and associated identification number, author, source, abstract, and summary of information (including types of data and parameters). AskSam{reg_sign}, a text-based database system, was chosen. WordPerfect 5.1{copyright} is being used as a text-editor to input data records into askSam.

  19. Pore-water isotopic compositions and unsaturated-zone flow, Yucca Mountain, Nevada

    SciTech Connect

    Yang, In C.

    2001-04-29

    Isotopic compositions of core-water samples from boreholes USW SD-6 and USW WT-24 indicate that recent water has been introduced at depth. Tritium, carbon, oxygen, and deuterium isotopic compositions all support younger water at depth in the two boreholes. Peaks in tritium concentrations in pore-water samples, indicating younger water than the other samples, observed near the basal vitrophyre of the Topopah Spring Tuff and at the bottom of the CHF and the top of the PP in both boreholes SD-6 and WT-24. Larger {sup 14}C activities in two pore-water samples from WT-24 at the bottom of the CHF and the top of the PP indicate younger water than in other samples from WT-24. More positive {delta}{sup 18}O and {delta}D values indicate younger water in samples of pore water at the bottom of the CHF in boreholes SD-6 and WT-24. The isotopic compositions indicating younger water at depth in boreholes SD-6 and WT-24 occur at the basal vitrophyre zone of the Topopah Spring Tuff and the bottom of the CHF/upper part of the PP, probably from lateral preferential flow through connected fractures (fast-flow paths). The source of the young water at borehole WT-24 probably was recharge from The Prow to the north, which then flowed laterally southward through the highly fractured TSw. The source of the young water at borehole SD-6 probably was water flow from the Solitario Canyon fault to the west, which then flowed laterally through the TSw and CHF.

  20. Consequences of using different soil texture determination methodologies for soil physical quality and unsaturated zone time lag estimates

    NASA Astrophysics Data System (ADS)

    Fenton, O.; Vero, S.; Ibrahim, T. G.; Murphy, P. N. C.; Sherriff, S. C.; Ó hUallacháin, D.

    2015-11-01

    Elucidation of when the loss of pollutants, below the rooting zone in agricultural landscapes, affects water quality is important when assessing the efficacy of mitigation measures. Investigation of this inherent time lag (tT) is divided into unsaturated (tu) and saturated (ts) components. The duration of these components relative to each other differs depending on soil characteristics and the landscape position. The present field study focuses on tu estimation in a scenario where the saturated zone is likely to constitute a higher proportion of tT. In such instances, or where only initial breakthrough (IBT) or centre of mass (COM) is of interest, utilisation of site and depth specific "simple" textural class or actual sand-silt-clay percentages to generate soil water characteristic curves with associated soil hydraulic parameters is acceptable. With the same data it is also possible to estimate a soil physical quality (S) parameter for each soil layer which can be used to infer many other physical, chemical and biological quality indicators. In this study, hand texturing in the field was used to determine textural classes of a soil profile. Laboratory methods, including hydrometer, pipette and laser diffraction methods were used to determine actual sand-silt-clay percentages of sections of the same soil profile. Results showed that in terms of S, hand texturing resulted in a lower index value (inferring a degraded soil) than that of pipette, hydrometer and laser equivalents. There was no difference between S index values determined using the pipette, hydrometer and laser diffraction methods. The difference between the three laboratory methods on both the IBT and COM stages of tu were negligible, and in this instance were unlikely to affect either groundwater monitoring decisions, or to be of consequence from a policy perspective. When tu estimates are made over the full depth of the vadose zone, which may extend to several metres, errors resulting from the use of

  1. Consequences of using different soil texture determination methodologies for soil physical quality and unsaturated zone time lag estimates.

    PubMed

    Fenton, O; Vero, S; Ibrahim, T G; Murphy, P N C; Sherriff, S C; Ó hUallacháin, D

    2015-11-01

    Elucidation of when the loss of pollutants, below the rooting zone in agricultural landscapes, affects water quality is important when assessing the efficacy of mitigation measures. Investigation of this inherent time lag (t(T)) is divided into unsaturated (t(u)) and saturated (t(s)) components. The duration of these components relative to each other differs depending on soil characteristics and the landscape position. The present field study focuses on tu estimation in a scenario where the saturated zone is likely to constitute a higher proportion of t(T). In such instances, or where only initial breakthrough (IBT) or centre of mass (COM) is of interest, utilisation of site and depth specific "simple" textural class or actual sand-silt-clay percentages to generate soil water characteristic curves with associated soil hydraulic parameters is acceptable. With the same data it is also possible to estimate a soil physical quality (S) parameter for each soil layer which can be used to infer many other physical, chemical and biological quality indicators. In this study, hand texturing in the field was used to determine textural classes of a soil profile. Laboratory methods, including hydrometer, pipette and laser diffraction methods were used to determine actual sand-silt-clay percentages of sections of the same soil profile. Results showed that in terms of S, hand texturing resulted in a lower index value (inferring a degraded soil) than that of pipette, hydrometer and laser equivalents. There was no difference between S index values determined using the pipette, hydrometer and laser diffraction methods. The difference between the three laboratory methods on both the IBT and COM stages of t(u) were negligible, and in this instance were unlikely to affect either groundwater monitoring decisions, or to be of consequence from a policy perspective. When t(u) estimates are made over the full depth of the vadose zone, which may extend to several metres, errors resulting from

  2. Evaluation of soil, unsaturated, and saturated zone parameter uncertainty using GSFlow and PEST in an agricultural watershed

    NASA Astrophysics Data System (ADS)

    Zuidema, S.; Davis, J. M.

    2011-12-01

    summer and fall of 2011, including improved resolution streamflow data from a recently installed Parshall flume on the small stream draining the majority of the farm. The relative contribution of the three measurement types to the overall model objective function, and parameter uncertainty from the PRMS soil zone, and MODFLOW saturated and unsaturated zones are used to assess data needed to improve the validity of water balance estimates, and suggest which model components may be least determined in similar coupled models.

  3. Atrazine adsorption and colloid-facilitated transport through the unsaturated zone

    USGS Publications Warehouse

    Sprague, L.A.; Herman, J.S.; Hornberger, G.M.; Mills, A.L.

    2000-01-01

    One explanation for unexpectedly widespread ground water contamination from atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) may be the occurence of colloid-facilitated transport, whereby the dissolved herbicide becomes adsorbed to mobile colloids that migrate through preferential flow-paths in the soil zone and into the ground water. The objectives of this study were to determine the extent of adsorpton of atrazine to bulk soil and to soil colloids and to determine the extent of colloid-facilitated transport of atrazine at a field site in Virginia during simulated rainfall events. Equilibrium batch adsorption experiments were performed over a concentration range of 0.05 to 10.0 mg atrazine L-1 on bulk soil samples and on colloidal suspensions of 75 mg L-1, a concentration comparable with those observed at the field site. Linear partition coefficients ranged from 0.496 to 2.48 L kg-1 for the bulk soil and from 70.8 to 832 L kg-1 for the soil colloids. In the field, gravity lysimeters were insured at a depth of 25 cm below the surface of six 0.25-m2 undisturbed plots. Mass recovery of surface-applied atrazine in the lysimeters was not significantly affected by rainfall rate and was, on average, 2.7% for plots receiving 25 mm h-1 simulated rainfall and 3.6% for plots receiving 50 mm h-1 simulated rainfall. Of the total atrazine collected in the lysimeters, the fraction that was colloid-associated ranged from 4.9 to 30% (mean of 15%), indicating that a measurable portion of mobile atrazine is transported via association with colloids.One explanation for unexpectedly widespread ground water contamination from atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) may be the occurrence of colloid-facilitated transport, whereby the dissolved herbicide becomes adsorbed to mobile colloids that migrate through preferential flow-paths in the soil zone and into the ground water. The objectives of this study were to determine the extent of adsorption of

  4. Impacts of land use change on nitrogen cycling archived in semiarid unsaturated zone nitrate profiles, southern High Plains, Texas.

    PubMed

    Scanlon, Bridget R; Reedy, Robert C; Bronson, Kevin F

    2008-10-15

    Nitrate (NO3) profiles in semiarid unsaturated zones archive land use change (LUC) impacts on nitrogen (N) cycling with implications for agricultural N management and groundwater quality. This study quantified LUC impacts on NO3 inventories and fluxes by measuring NO3 profiles beneath natural and rainfed (nonirrigated) agricultural ecosystems in the southern High Plains (SHP). Inventories of NO3-N under natural ecosystems in the SHP normalized by profile depth are extremely low (2-10 kg NO3-N/ha/m), in contrast to those in many semiarid regions in the southwestern U.S. Many profiles beneath cropland (9 of 19 profiles) have inventories at depth that range from 28-580 kg NO3--N/ha/m (median 135 kg/ha/m) that correspond to initial cultivation, dated using soil water Cl. These inventories represent 74% (median) of the total inventories in these profiles. This NO3 most likely originated from cultivation causing mineralization and nitrification of soil organic nitrogen (SON) in old soil water (precultivation) and is attributed to enhanced microbial activity caused by increased soil wetness beneath cropland (median matric potential -42 m) relative to that beneath natural ecosystems (median -211 m). The SON source is supported by isotopes of NO3 (delta15N: +5.3 to +11.6; delta18O: +3.6 to +12.1). Limited data in South Australia suggest similar processes beneath cropland. Mobilization of the total inventories in these profiles caused by increased drainage/ recharge related to cultivation in the SHP could increase current NO3-N levels in the underlying Ogallala aquifer by an additional 2-26 mg/L (median 17 mg/L). PMID:18983076

  5. Tracking sources of unsaturated zone and groundwater nitrate contamination using nitrogen and oxygen stable isotopes at the Hanford site, Washington.

    PubMed

    Singleton, Michael J; Woods, Katharine N; Conrad, Mark E; Depaolo, Donald J; Dresel, P Evan

    2005-05-15

    The nitrogen and oxygen isotopic compositions of nitrate in pore water extracts from unsaturated zone (UZ) core samples and groundwater samples indicate at least four potential sources of nitrate in groundwaters at the U.S. DOE Hanford Site in south-central Washington. Natural sources of nitrate identified include microbially produced nitrate from the soil column (delta15N of 4 - 8 per thousand, delta18O of -9 to 2 per thousand) and nitrate in buried caliche layers (delta15N of 0-8 per thousand, delta 18O of -6to 42 per thousand). Isotopically distinctindustrial sources of nitrate include nitric acid in low-level disposal waters (delta15N approximately per thousand, delta 18O approximately 23%o) per thousandnd co-contaminant nitrate in high-level radioactive waste from plutonium processing (6'5delta1of 8-33 % o, per thousand18delta oO -9 to 7%0). per thousandThe isotopic compositions of nitrate from 97 groundwater wells with concentrations up to 1290 mg/L NO3- have been analyzed. Stable isotope analyses from this study site, which has natural and industrial nitrate sources, provide a tool to distinguish nitrate sources in an unconfined aquiferwhere concentrations alone do not. These data indicate that the most common sources of high nitrate concentrations in groundwater at Hanford are nitric acid and natural nitrate flushed out of the UZ during disposal of low-level wastewater. Nitrate associated with high-level radioactive UZ contamination does not appear to be a major source of groundwater nitrate at this time. PMID:15952359

  6. Isotope Geochemistry of Calcite Coatings and the Thermal History of the Unsaturated Zone at Yucca Mountain, Nevada

    SciTech Connect

    B.D. Marshall; J.F. Whelan

    2000-07-27

    Calcite and opal coatings found on fracture footwalls and lithophysal cavity bottoms in the volcanic section at Yucca Mountain (exposed in a tunnel) contain a record of gradual chemical and isotopic changes that have occurred in the unsaturated zone. The thin (less than 6 cm) coatings are composed primarily of calcite, opal, chalcedony, and quartz. Fluid inclusions in calcite that homogenize at greater than ambient temperatures provide impetus for geochronologic studies in order to determine the thermal history. In the welded Topopah Spring Tuff (12.7 Ma), U-Pb ages of opal and chalcedony layers provide evidence of a long history of deposition throughout the past 10 m.y. However, these ages can constrain the ages of associated calcite layers only in samples with an easily interpretable microstratigraphy. Strontium isotope ratios in calcite increase with microstratigraphic position from the base up to the outermost surface of the coatings. The strontium incorporated in these coatings records the systematic change in pore-water isotopic composition due to water-rock interaction primarily in the overlying nonwelded tuffs. A one-dimensional advection-reaction model simulates strontium isotope ratios measured in pore water extracted from core in three vertical boreholes adjacent to the tunnel. By calculating the strontium isotope compositions of the rocks at various past times, the model predicts a history of the strontium isotope ratios in the water that matches the record in the calcite and therefore provides approximate ages. Oxygen isotope ratios measured in calcite gradually increase with decreasing model strontium age. Assuming that the oxygen isotope ratio of the percolating water was relatively constant, this trend indicates a gradual cooling of the rocks over millions of years, in agreement with thermal modeling of magma beneath the 12-Ma Timber Mountain caldera just north of Yucca Mountain. This model predicts that temperatures significantly exceeding current

  7. Measuring Total Flux of Organic Vapors From the Unsaturated Zone Under Natural Conditions: Design, Laboratory and Field Testing of a Flux Chamber Device

    NASA Astrophysics Data System (ADS)

    Tillman, F. D.; Choi, J.; Smith, J. A.

    2002-05-01

    A simple, easy-to-use, and inexpensive device for measuring VOC flux under natural conditions was designed and tested both in a controlled laboratory environment and in a natural field setting. The chamber consists of a stainless-steel right circular cylinder open on one end with a flexible, impermeable membrane allowing for chamber expansion and contraction. Air is pumped from inside the chamber through activated carbon traps and returned to the chamber maintaining a net zero pressure gradient from the inside to the outside of the chamber. The traps are analyzed using thermal desorption/GC-FID and the mass of contaminant is divided by the product of the sampled area and sample time to give VOC flux measured by the chamber. Design parameters for the chamber were selected using continuously stirred tank reactor (CSTR)-equation based modeling under step, sinusoidal and transport-model simulation flux inputs. Laboratory testing of the flux chamber under both diffusion and advection dominated conditions was performed in a device constructed to simulate unsaturated zone transport. Aqueous trichloroethene (TCE) solution was pumped through the bottom of a steel drum inside which 50-cm of fine sand was suspended. For diffusion-dominated transport experiments, the chamber was installed in the sand at the top of the simulator and operated in the same manner as would occur in the field. The flux measurement of the chamber was then compared to flux prediction based on measured linear concentration data from the simulator and Fick's law. Advective transport is initiated in the vadose zone simulator by flowing humidified, pressurized air into an input port in the bottom of the simulator below the suspended porous media. Soil-gas velocity is calculated by dividing the airflow input by the surface area of the simulator. Flux was measured with the chamber and compared to flux predicted using airflow and concentration data from the simulator. Results from both the diffusion-only and

  8. A Film Depositional Model of Permeability for Mineral Reactions in Unsaturated Media.

    SciTech Connect

    Freedman, Vicky L.; Saripalli, Prasad; Bacon, Diana H.; Meyer, Philip D.

    2004-11-15

    A new modeling approach based on the biofilm models of Taylor et al. (1990, Water Resources Research, 26, 2153-2159) has been developed for modeling changes in porosity and permeability in saturated porous media and implemented in an inorganic reactive transport code. Application of the film depositional models to mineral precipitation and dissolution reactions requires that calculations of mineral films be dynamically changing as a function of time dependent reaction processes. Since calculations of film thicknesses do not consider mineral density, results show that the film porosity model does not adequately describe volumetric changes in the porous medium. These effects can be included in permeability calculations by coupling the film permeability models (Mualem and Childs and Collis-George) to a volumetric model that incorporates both mineral density and reactive surface area. Model simulations demonstrate that an important difference between the biofilm and mineral film models is in the translation of changes in mineral radii to changes in pore space. Including the effect of tortuosity on pore radii changes improves the performance of the Mualem permeability model for both precipitation and dissolution. Results from simulation of simultaneous dissolution and secondary mineral precipitation provides reasonable estimates of porosity and permeability. Moreover, a comparison of experimental and simulated data show that the model yields qualitatively reasonable results for permeability changes due to solid-aqueous phase reactions.

  9. Modeling the fate of radionuclides in the unsaturated zone at the Nevada Test Site: Examples from Yucca Flat and Rainier Mesa

    NASA Astrophysics Data System (ADS)

    Kwicklis, E. M.; Dash, Z. V.; Viswanathan, H. S.; Levitt, D. G.; Lu, Z.; Dai, Z.; Zyvoloski, G.; Gable, C. W.; Miller, T. A.

    2010-12-01

    The Nevada Test Site (NTS), located 105 km northwest of Las Vegas, Nevada, hosted 828 underground nuclear explosions between 1951 and 1992, leaving an estimated 1.3e+08 curies of tritium, fission products, activation products and unspent fuel in the subsurface when the nuclear test moratorium was adopted in September, 1992. In two former testing areas of the NTS - Yucca Flat and Rainier Mesa- a significant fraction of the initial radionuclide inventory was introduced from nuclear tests with working points in the unsaturated zone. In Yucca Flat, an arid, low-elevation alluvium-filled basin where most tests were conducted in vertical shafts, unsaturated flow and transport models indicate that radionuclide migration to the water table is most likely where overlying subsidence craters receive significant infiltration from overland flow during infrequent runoff events. At Rainier Mesa, a wetter, high-elevation remnant of a once more extensive volcanic plateau, most tests were conducted at the ends of horizontal drifts in the vicinity of local perched water zones. Unsaturated flow and transport models of one of the larger tunnel complexes (N-tunnel) indicate that despite relatively high infiltration rates on the mesa, radionuclide diffusion from the flowing fractures to the porous matrix may significantly attenuate radionuclide movement to the water table.

  10. Effect of viscous cross coupling between two immiscible fluids on elastic wave propagation and attenuation in unsaturated porous media

    NASA Astrophysics Data System (ADS)

    Lo, Wei-Cheng; Yeh, Chao-Lung; Lee, Jhe-Wei

    2015-09-01

    A central issue in the theoretical treatment of a multiphase system is the proper mathematical description of momentum transfer across fluid-solid and fluid-fluid interfaces. Although recent studies have advanced our knowledge on modeling the coupling behavior between a porous framework and the fluids permeating it, the effect of viscous resistance caused by two-fluid flow on elastic wave behavior in unsaturated porous media still remains elusive. In the present study, the theoretical model developed for describing immiscible two-phase fluid flows in a deformable porous medium related to harmonic wave perturbation is generalized to account for viscous cross coupling due to relative velocity between two adjacent fluids. The corresponding dispersion relations whose coefficients feature all elasticity, inertial-drag, and viscous-drag parameters are then precisely formulated, in a physical context characterizing three compressional waves and one shear wave. To evaluate quantitatively this as-yet unknown effect, numerical calculations are conducted to solve the dispersion relations for Columbia fine sandy loam bearing an oil-water mixture as a function of water saturation and excitation frequency. Our results show that the phase speed and attenuation coefficient of the P3 wave which has the smallest speed is strongly sensitive to the presence of viscous cross coupling, as expected since this wave is attributed primarily to the out-of-phase motion of the two pore fluids. Viscous cross coupling also exerts an impact on the attenuation coefficient of the shear wave and the P1 wave whose speed is greatest, which exhibits two opposite trends at different ranges of low and high water contents. Relative differences in these wave attributes are principally independent of excitation frequency. A sensitivity analysis is carried out to assess how changes in viscous cross coupling affect these differences, revealing that some of them become more significant as viscous cross

  11. Busted Butte Unsaturated Zone Transport Test: Fiscal Year 1998 Status Report Yucca Mountain Site Characterization Program Deliverable SPU85M4

    SciTech Connect

    Bussod, G.Y.; Turin, H.J.; Lowry, W.E.

    1999-11-01

    This report describes the status of the Busted Butte Unsaturated Zone Transport Test (UZTT) and documents the progress of construction activities and site and laboratory characterization activities undertaken in fiscal year 1998. Also presented are predictive flow-and-transport simulations for Test Phases 1 and 2 of testing and the preliminary results and status of these test phases. Future anticipated results obtained from unsaturated-zone (UZ) transport testing in the Calico Hills Formation at Busted Butte are also discussed in view of their importance to performance assessment (PA) needs to build confidence in and reduce the uncertainty of site-scale flow-and-transport models and their abstractions for performance for license application. The principal objectives of the test are to address uncertainties associated with flow and transport in the UZ site-process models for Yucca Mountain, as identified by the PA working group in February 1997. These include but are not restricted to: (1) The effect of heterogeneities on flow and transport in unsaturated and partially saturated conditions in the Calico Hills Formation. In particular, the test aims to address issues relevant to fracture-matrix interactions and permeability contrast boundaries; (2) The migration behavior of colloids in fractured and unfractured Calico Hills rocks; (3) The validation through field testing of laboratory sorption experiments in unsaturated Calico Hills rocks; (4) The evaluation of the 3-D site-scale flow-and-transport process model (i.e., equivalent-continuum/dual-permeability/discrete-fracture-fault representations of flow and transport) used in the PA abstractions for license application; and (5) The effect of scaling from lab scale to field scale and site scale.

  12. A Mixing-Cell Model for Assessment of Contaminant Transport in the Unsaturated Zone Under Steady-State and Transient Flow Conditions

    SciTech Connect

    Arthur S. Rood

    2004-11-01

    A one-dimensional model for water flow and solute transport in the unsaturated zone under steady-state or transient flow conditions was developed from the principles of the mixing-cell model. The unsaturated zone is discretized into a series of independent mixing cells. Each cell may have unique hydrologic, lithologic, and sorptive properties. Ordinary differential equations (ODE) describe the material (water and solute) balance within each cell. Water flow equations are derived from the continuity equation assuming that unit-gradient conditions exist at all times in each cell. Pressure gradients are considered implicitly through model discretization. Unsaturated hydraulic conductivity and moisture contents are determined by the material-specific moisture characteristic curves. Solute transport processes included explicit treatment of advective processes, first-order chain decay, and linear sorption reactions. Dispersion is addressed through implicit and explicit dispersion. Implicit dispersion is an inherent feature of all mixing cell models and originates from the formulation of the problem in terms of mass balance around fully mixed volume elements. Expressions are provided that relate implicit dispersion to the physical dispersion of the system. The system of ODEs was solved using a forth-order Runge-Kutta algorithm coupled with adaptive step size control. Computer run times for transient flow and solute transport were typically several seconds on a 2-GHz Intel Pentium IV® desktop computer. The model was benchmarked against analytical solutions and finite-element approximations to the partial differential equations (PDE) describing unsaturated flow and transport. Differences between the maximum solute flux estimated by the mixing-cell model and the PDE models were typically less than 2%.

  13. Composition and Transport of Volatile Organic Compounds Near a Chemical and Radioactive Waste Disposal Facility in an Arid Environment with a Thick Unsaturated Zone

    NASA Astrophysics Data System (ADS)

    Baker, R. J.; Andraski, B. J.; Stonestrom, D. A.; Luo, W.

    2010-12-01

    Volatile organic compounds (VOCs) and low-level radioactive waste (LLRW) materials commonly occur together in mixed-waste disposal facilities. Volatile components of both waste types can be transported simultaneously away from the site through the unsaturated zone. Concentrations, variability, and transport of VOCs near mixed-waste-disposal facilities in arid environments remain poorly understood. In this study, plume-scale VOC composition of the deep and shallow unsaturated zone near such a facility in southwestern Nevada was observed over a 10-year period. Spatial and temporal variability of VOC concentrations were monitored, and vertical (upward) fluxes of VOCs through the unsaturated zone to the land surface were estimated. Vapor-phase samples were collected from two boreholes, each instrumented with 10-12 vapor-sampling ports at irregular intervals that extend the entire depth of the110-m unsaturated zone and are located 100 and 160 m away from the nearest LLRW trench. Also, an array of eight shallow (0.5- and 1.5-m depths) vapor-probe sets extending from 0-400 m from the LLRW facility was monitored. Chlorfluorocarbons (CFCs) constitute ~60 percent of total VOC mass, far more than any other compound or class. Chlorinated solvent chemicals (~29 percent) and gasoline-range hydrocarbons (~1 percent) also were detected in most sampling locations. Shallow and deep samples indicate VOC concentrations in the vapor plume are increasing with time and moving further off site. The highest total VOC concentration observed was about 47,000 ppbv. Vertical profiles of VOC concentrations implies a preferential lateral flow path at 20-40 m below land surface, and upward and downward diffusive fluxes away from the zone of peak concentrations. The coarse gravel in this depth interval appears to provide less resistance to vapor-phase transport than the finer-textured sediment layers above and below. VOC concentrations at 0.5 and 1.5 m below land surface and laboratory

  14. Sensors and Monitoring Techniques for the Deep Unsaturated Zone: Reducing Uncertainty Related to Seepage and Transport in Fractured Rock

    NASA Astrophysics Data System (ADS)

    Dinwiddie, C. L.; Or, D.; Stothoff, S. A.; Fedors, R. W.; Pohle, J. A.; Tuller, M.

    2007-12-01

    Planning for performance confirmation of hydrologic properties and processes in a potential geologic repository for high-level radioactive waste at Yucca Mountain is a requirement stated in Subpart F of 10 CFR Part 63. An important goal of performance confirmation is to acquire information indicating whether natural and engineered barriers are functioning as intended, and whether the conditions encountered are within the limits assumed during a licensing review. Long-term monitoring of hydrologic properties and processes and in situ confirmation of design assumptions will play a key role in the safe operation of the potential geologic radioactive waste repository and in the decision to close the repository. Despite remarkable advances in cyberinfrastructure for linking sensors into spatially distributed environmental networks, the extended time horizon (decades to hundreds of years) for long-term monitoring activities, the harsh thermal and radiative conditions in the near-field environment, the deep fractured unsaturated rock environment at Yucca Mountain, the potential scope of observations, and restricted access to observation ports for maintenance and upgrades each present unprecedented challenges to the design of hydro-environmental monitoring networks. Activities for performance confirmation could include the use of pore water samplers and sensors for measuring water content, matric potential, temperature, relative humidity, and water and gas fluxes. Current sensor technology for deep fractured rock systems (i) lags behind environmental observatory network solutions for surface and near-surface processes, (ii) lags behind analogous technology for unconsolidated porous media, (iii) cannot be reliably deployed without ongoing maintenance or replacement at relatively frequent intervals, and (iv) is not designed to withstand harsh thermal and radiative conditions. Long-term monitoring could require special design considerations, such as measurement redundancy

  15. Effects of low-level radioactive-waste disposal on water chemistry in the unsaturated zone at a site near Sheffield, Illinois, 1982-84

    USGS Publications Warehouse

    Peters, C.A.; Striegl, R.G.; Mills, P.C.; Healy, R.W.

    1992-01-01

    A 1982-84 field study defined the chemistry of water collected from the unsaturated zone at a low-level radioactive-waste disposal site near Sheffield, Bureau County, Ill. Chemical data were evaluated to determine the principal, naturally occurring geochemical reactions in the unsaturated zone and to evaluate waste-induced effects on pore-water chemistry. Samples of precipitation, unsaturated-zone pore water, and saturated-zone water were analyzed for specific conductance, pH, alkalinity, major cations and anions, dissolved organic carbon, gross alpha and beta radiation, and tritium. Little change in concentration of most major constituents in the unsaturated-zone water was observed with respect to depth or distance from disposal trenches. Tritium and dissolved organic carbon concentrations were, however, dependent on proximity to trenches. The primary reactions, both on-site and off-site, were carbonate and clay dissolution, cation exchange, and the oxidation of pyrite. The major difference between on-site and off-site inorganic water chemistry resulted from the removal of the Roxana Silt and the Radnor Till Member of the Glasford Formation from on-site. Off-site, the Roxana Silt contributed substantial quantities of sodium to solution from montmorillonite dissolution and associated cation-exchange reactions. The Radnor Till Member provided exchange surfaces for magnesium. Precipitation at the site had an ionic composition of calcium zinc sulfate and an average pH of 4.6. Within 0.3 meter of the land surface, infiltrating rainwater or snowmelt changed to an ionic composition of calcium sulfate off-site and calcium bicarbonate on-site and had an average pH of 7.9; below that depth, pH averaged 7.5 and the ionic composition generally was calcium magnesium bicarbonate. Alkalinity and specific conductance differed primarily according to composition of geologic materials. Tritium concentrations ranged from 0.2 (detection limit) to 1,380 nanocuries per liter. The

  16. Effects of low-level radioactive-waste disposal on water chemistry in the unsaturated zone at a site near Sheffield, Illinois, 1982-84

    USGS Publications Warehouse

    Peters, C.A.; Striegl, R.G.; Mills, P.C.; Healy, R.W.

    1992-01-01

    A 1982-84 field study defined the chemistry of water collected from the unsaturated zone at a low-level radioactive-waste disposal site near Sheffield, Bureau County, Illinois. Chemical data were evaluated to determine the principal naturally occurring geochemical reactions in the unsaturated zone and to evaluate waste-induced effects on pore-water chemistry. Samples of precipitation, unsaturated-zone pore water, and saturated-zone water were analyzed for specific conductance, pH, alkalinity, major cations and anions, dissolved organic carbon, gross alpha and beta radiation, and tritium. Little change in concentration of most major constituents in the unsaturated-zone water was observed with respect to depth or distance from disposal trenches. Tritium and dissolved organic carbon concentrations were, however, dependent on proximity to trenches. The primary reactions, both on- site and off-site, were carbonate and clay dissolution, cation exchange, and the oxidation of pyrite. The major difference between on-site and off-site inorganic water chemistry resulted from the removal of the Roxana Silt and the Radnor Till Member of the Glasford Formation from on-site. Off-site, the Roxana Silt contributed substantial quantities of sodium to solution from montmorillonite dissolution and associated cation-exchange reactions. The Radnor Till Member provided exchange surfaces for magnesium. Precipitation at the site had an ionic composition of calcium zinc sulfate and an average pH of 4.6. Within 0.3 meter of the land surface, infiltrating rain water or snowmelt changed to an ionic canposition of calcium sulfate off-site and calcium bicarbonate on-site and had an average pH of 7.9; below that depth, pH averaged 7.5 and the ionic composition generally was calcium magnesium bicarbonate. Alkalinity and specific conductance differed primarily according to composition of geologic materials. Tritium concentrations ranged from 0.2 (detection limit) to 1,380 nanocuries per liter. The

  17. Physical and stable-isotope evidence for formation of secondary calcite and silica in the unsaturated zone, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Whelan, J.F.; Paces, J.B.; Peterman, Z.E.

    2002-01-01

    Calcite and silica form coatings on fracture footwalls and cavity floors in the welded tuffs at Yucca Mountain, the potential site of a high-level radioactive waste repository. These secondary mineral deposits are heterogeneously distributed in the unsaturated zone (UZ) with fewer than 10% of possible depositional sites mineralized. The paragenetic sequence, compiled from deposits throughout the UZ, consists of an early-stage assemblage of calcite??fluorite??zeolites that is frequently capped by chalcedony??quartz. Intermediate- and late-stage deposits consist largely of calcite, commonly with opal on buried growth layers or outermost crystal faces of the calcite. Coatings on steep-dipping fractures usually are thin (??? 3 mm) with low-relief outer surfaces whereas shallow-dipping fractures and lithophysal cavities typically contain thicker, more coarsely crystalline deposits characterized by unusual thin, tabular calcite blades up to several cms in length. These blades may be capped with knobby or corniced overgrowths of late-stage calcite intergrown with opal. The observed textures in the fracture and cavity deposits are consistent with deposition from films of water fingering down fracture footwalls or drawn up faces of growing crystals by surface tension and evaporated at the crystal tips. Fluid inclusion studies have shown that most early-stage and some intermediate-stage calcite formed at temperatures of 35 to 85??C. Calcite deposition during the past several million years appears to have been at temperatures < 30??C. The elevated temperatures indicated by the fluid inclusions are consistent with temperatures estimated from calcite ??18O values. Although others have interpreted the elevated temperatures as evidence of hydrothermal activity and flooding of the tuffs of the potential repository, the authors conclude that the temperatures and fluid-inclusion assemblages are consistent with deposition in a UZ environment that experienced prolonged heat input from

  18. Chemical, isotopic, and microbiological evidence for denitrification during transport of domestic wastewater through a thick unsaturated zone in the Mojave Desert, San Bernardino County, California

    USGS Publications Warehouse

    Schroeder, R.A.; Martin, P.M.; Böhlke, J.K.

    1993-01-01

    Nitrogen in downward-infiltrating wastewater discharged from seepage pits (dry wells) at residences in the upper Mojave River Basin, California represents a significant potential source of nitrate contamination to the underlying ground water. However, increases in nitrate concentration in the ground water have not yet been observed. The low nitrate concentration in the ground water may be the result of lateral dispersion in the unsaturated zone, dilution below the water table, or denitrification of wastewater nitrate in the unsaturated zone. Measured vertical rates indicate that some wastewater has reached the water table beneath communities that are older than 5 to 10 years. As wastewater percolates from seepage pits into the unsaturated zone, reduced nitrogen is converted rapidly to nitrate at shallow depths and the nitrate concentrations commonly decrease with depth. The largest nitrate decreases seem to coincide with increased content of fine-grained sediments or with proximity to the water table. Between lysimeters at 160 and 199 feet at one residence, the decrease in nitrate concentration coincided with a large increase in sulfate, decrease in alkalinity, and increase in 815N in nitrate. Those data are consistent with denitrification by oxidation of iron sulfide to produce ferric oxides; but if such a reaction occurs, it must be in domains that are small in comparison with the sampled volumes because the waters also contain substantial quantities of dissolved oxygen. The predominantly low nitrate concentrations in the area's ground water are consistent with the operation of a nitrogen-removal mechanism, possibly denitrification; however, the reducing capacity of the sediments to maintain denitrification is not known.

  19. Tritium in unsaturated zone gases and air at the Amargosa Desert Research Site, and in spring and river water, near Beatty, Nevada, May 1997

    USGS Publications Warehouse

    Striegl, R.G.; Healy, R.W.; Michel, R.L.; Prudic, D.E.

    1998-01-01

    Elevated tritium concentrations in the unsaturated zone at the Amargosa Desert Research Site (ADRS), immediately south and west of the low-level radioactive-waste burial site south of Beatty, Nevada, have stimulated research of processes that control the transport of tritium in arid unsaturated zones. In May 1997, 58 samples were collected from 1.5 m (meters) depth within a 250 m by 250 m grid at the ADRS. Measured concentrations ranged from 16 ? 9 to 36,900 ? 300 tritium units (TU), decreasing from northeast to southwest, possibly along an ancestral Amargosa River channel. The 10 air ports at test hole UZB-2 also were sampled, including ports at 57.6, 106.4, and 108.8 m depths that had not been sampled since 1994. Of the remaining seven ports, five were sampled in 1994, 1995, and 1996, and two were sampled in 1994 and 1996. Tritium concentrations at the four ports deeper than 50 m ranged from 791 ? 15 to 1765 ? 29 TU, having increased since they were last sampled. Tritium concentrations at the six ports shallower than 50 m ranged from 367 ? 11 to 1283 ? 20 TU, and appear to have stabilized since 1996. Tritium concentration in water vapor collected from air within the creosote bush canopy was 75 ? 9 TU near test hole UZB-2 and 9 ? 6 TU near the uncontaminated Fischer test hole, 3.2 km to the south. Elevated tritium concentration in air near test hole UZB-2 was attributed to plant transpiration removing water from the unsaturated zone. Nearby surface water tritium concentrations were 6.3 ? 0.4 TU at Specie Spring, 0.0 ? 0.3 TU at Lower Indian Springs and at Upper Indian Springs, and 0.8 ? 0.6 TU in Amargosa River water.

  20. Spatio-temporal groundwater recharge assessment using a lumped-parameter distributed model of the unsaturated zone (pyEARTH-2D)

    NASA Astrophysics Data System (ADS)

    Francés, Alain Pascal; Berhe, Ermias; Lubczynski, Maciek

    2010-05-01

    Numerical flow models are nowadays a powerful and widely used tool for groundwater management. Their reliability requires both an accurate physical representation of an aquifer system and appropriate boundary conditions. While the hydraulic parameters like hydraulic conductivity (K) and storativity (S) are spatially dependent and time invariant, groundwater fluxes such as recharge (R), evapotranspiration from groundwater (ETg) and groundwater inflow/outflow (Qgw) can vary in both space and time. Multiplicity of combinations between parameters and fluxes leads to a non-uniqueness of model solutions which limits their reliability and forecasting capability. We propose to constrain groundwater models at the catchment scale by the spatio-temporal assessment of fluxes in the unsaturated zone. Although the physically based models that involve the Darcy's law and the conservation of mass through the Richard's equation constitute the most appropriate tools for fluxes assessment in the unsaturated zone, they are computationally demanding and require a complex parameterization and boundary condition definition, which restricts their application to large and regional scales. We have thus chosen to develop and apply a lumped-parameter unsaturated zone model because it uses simplified representations of the physical processes and limits the number of parameters. We present in this study the development and application of a spatio-temporal recharge model (pyEARTH-2D) coupled with the numerical flow model MODFLOW at the catchment scale. pyEARTH-2D is a lumped-parameter distributed (grid-based) model that shares the same spatial discretization of the MODFLOW model for coupling purpose. pyEARTH-2D solves the water balance in the topsoil layer using linear relations between fluxes and soil moisture on a daily basis. The partitioning of rainfall is done by taking into consideration interception, evapotranspiration, percolation, soil moisture storage and surface storage and runoff

  1. Analyzing unsaturated flow patterns in fractured rock using an integrated modeling approach

    NASA Astrophysics Data System (ADS)

    Wu, Yu-Shu; Lu, Guoping; Zhang, Keni; Pan, Lehua; Bodvarsson, Gudmundur S.

    2007-05-01

    Characterizing percolation patterns in unsaturated fractured rock has posed a greater challenge to modeling investigations than comparable saturated zone studies due to the heterogeneous nature of unsaturated media and the great number of variables impacting unsaturated flow. An integrated modeling methodology has been developed for quantitatively characterizing percolation patterns in the unsaturated zone of Yucca Mountain, Nevada (USA), a proposed underground repository site for storing high-level radioactive waste. The approach integrates moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model for analyses. It takes into account the coupled processes of fluid and heat flow and chemical isotopic transport in Yucca Mountain’s highly heterogeneous, unsaturated fractured tuffs. Modeling results are examined against different types of field-measured data and then used to evaluate different hydrogeological conceptualizations through analyzing flow patterns in the unsaturated zone. In particular, this model provides clearer understanding of percolation patterns and flow behavior through the unsaturated zone, both crucial issues in assessing repository performance. The integrated approach for quantifying Yucca Mountain’s flow system is demonstrated to provide a practical modeling tool for characterizing flow and transport processes in complex subsurface systems.

  2. Flow and Radionuclide Transport Models of the Unsaturated Zone at the Nevada National Security Site: Examples from Yucca Flat and Rainier Mesa

    NASA Astrophysics Data System (ADS)

    Kwicklis, E. M.; Viswanathan, H. S.; Levitt, D. G.; Dash, Z.; Gable, C. W.; Lu, Z.; Dai, Z.; Zyvoloski, G.; Miller, T. A.

    2011-12-01

    The former Nevada Test Site (now the Nevada National Security Site) hosted 828 underground nuclear explosions between 1951 and 1992, leaving an estimated 1.3e+08 curies of tritium, fission products, activation products and unspent fuel in the subsurface when the nuclear test moratorium was adopted in September, 1992. In two former testing areas of the Nevada National Security Site - Yucca Flat and Rainier Mesa- a significant fraction of the initial radionuclide inventory was introduced from nuclear tests with working points in the unsaturated zone. In Yucca Flat, an arid, low-elevation alluvium-filled basin where most tests were conducted in vertical shafts, unsaturated flow and transport models indicate that radionuclide migration to the water table is most likely where overlying subsidence craters receive significant infiltration from overland flow during infrequent runoff events. These craters tend to be located along the perimeter of the basin and have large contributing watersheds in the surrounding hills. At Rainier Mesa, a wetter, high-elevation remnant of a once more extensive volcanic plateau, most tests were conducted at the ends of horizontal drifts in the vicinity of local perched water zones. Unsaturated flow and transport models of one of the larger tunnel complexes (N-tunnel) indicate that despite relatively high infiltration rates on the mesa, radionuclide diffusion from the flowing fractures to the porous matrix may significantly attenuate radionuclide movement to the water table, depending on the assumed fracture attributes. Simulations show that the tunnel itself may be an important hydraulic feature that connects radionuclide sources to sub-vertical faults that are assumed to extend to the water table.

  3. U-Pb Ages of Secondary Silica at Yucca Mountain, Nevada: Implications for the Paleohydrology of the Unsaturated Zone

    SciTech Connect

    L.A. Neymark; Y. Amelin; J.B. Paces; Z.E. Peterman

    2001-08-20

    U, Th, and Pb isotopes were analyzed in layers of opal and chalcedony from individual millimeter- to centimeter-thick calcite and silica coatings at Yucca Mountain, Nevada, USA, a site that is being evaluated for a potential high-level nuclear waste repository. These calcite and silica coatings on fractures and in lithophysal cavities in Miocene-age tuffs in the unsaturated zone (UZ) precipitated from descending water and record a long history of percolation through the UZ. Opal and chalcedony have high concentrations of U (10 to 780 ppm) and low concentrations of common Pb as indicated by large values of {sup 206}Pb/{sup 204}Pb (up to 53,806), thus making them suitable for U-Pb age determinations. Interpretations of U-Pb isotopes in opal samples at Yucca Mountain are complicated by the incorporation of excess {sup 234}U at the time of mineral formation, resulting in reverse discordance of U-Pb ages. However, the {sup 207}Pb/{sup 235}U ages are much less affected by deviation from initial secular equilibrium and provide reliable ages of most silica deposits between 0.6 and 9.8 Ma. For chalcedony subsamples showing normal age discordance, these ages may represent minimum times of deposition. Typically, {sup 207}Pb/{sup 235}U ages are consistent with the microstratigraphy in the mineral coating samples, such that the youngest ages are for subsamples from outer layers, intermediate ages are from inner layers, and oldest ages are from innermost layers. {sup 234}U and {sup 230}Th in most silica layers deeper in the coatings are in secular equilibrium with {sup 238}U, which is consistent with their old age and closed system behavior during the past 0.5 m.y. U-Pb ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from lithophysal cavities in the welded part of the Topopah Spring Tuff yield slow long-term average depositional rates of 1 to 5 mm/m.y. These data imply that the deeper

  4. Tritium Fluxes through the Shallow Unsaturated Zone adjacent to a Radioactive Waste Disposal Facility in an Arid Environment

    NASA Astrophysics Data System (ADS)

    Maples, S.; Andraski, B. J.; Stonestrom, D. A.; Cooper, C. A.; Pohll, G.

    2011-12-01

    Studies at the U.S. Geological Survey's Amargosa Desert Research Site (ADRS) in southern Nevada have documented long-distance (>400-m) tritium (3H) transport adjacent to a commercial, low-level radioactive waste disposal facility. Transport at this scale is orders of magnitude greater than anticipated; however, lateral 3H fluxes through the shallow unsaturated zone (UZ) have not been investigated in detail. The objective of this study is to estimate and compare lateral and vertical tritiated water-vapor (3HHOg) fluxes in the shallow UZ and their relation to the observed plume migration. Previous studies have recognized two distinct plumes of 3H emanating from the facility. Shallow (0.5 and 1.5-m depth) soil-water vapor samples were collected yearly along 400-m long transects through both plumes from 2003-09. Within the south plume, 3H concentrations at 1.5-m depth have decreased by 44 ± 0.3% during this period, and plume advancement there has effectively ceased (i.e., rate of advance equals rate of decay). During the same period, the west plume showed a net decrease in concentration of 34 ± 0.9% within 100-m of the facility; however, plume advancement is observed at the leading edge of the plume, and concentrations 200-300-m from the facility show an increase in 3H concentration of 64 ± 28.4%. Lateral and vertical diffusive fluxes within both plumes were calculated using 3HHOg concentrations from 2006. Lateral 3HHOg diffusive fluxes within both plumes have been estimated 25-300-m from the facility at 1.5-m depth. Mean lateral 3HHOg diffusive fluxes are 10-14 g m-2 yr-1 within the south plume, and 10-13 g m-2 yr-1 within the west plume. Mean lateral fluxes in the south plume are an order of magnitude lower than in the west plume. This behavior corresponds with the observed relative immobility of the south plume, while the elevated west plume fluxes agree with the plume advancement seen there. Shallow, upward directed, mean vertical 3HHOg fluxes 25-300-m from the

  5. A deuterium-based labeling technique for the investigation of rooting depths, water uptake dynamics and unsaturated zone water transport in semiarid environments

    NASA Astrophysics Data System (ADS)

    Beyer, M.; Koeniger, P.; Gaj, M.; Hamutoko, J. T.; Wanke, H.; Himmelsbach, T.

    2016-02-01

    Non- or minimum-invasive methods for the quantification of rooting depths of plants are rare, in particular in (semi-)arid regions; yet, this information is crucial for the parameterization of SVAT (Soil-Vegetation-Atmosphere Transfer) models and understanding of processes within the hydrological cycle. We present a technique utilizing the stable isotope deuterium (2H) applied as artificial tracer to investigate the vertical extent of the root zone, characterize water uptake dynamics of trees and shrubs at different depths and monitor transport of water through the unsaturated zone of dry environments. One liter of 35% deuterated water (2H2O) was punctually applied at several depths (0.5 m, 1 m, 2 m, 2.5 m and 4 m) at six different plots at a natural forested site in the Cuvelai-Etosha Basin (CEB), Namibia/Angola. Subsequently, uptake of the tracer was monitored by collecting plant samples (xylem and transpired water) up to seven days after tracer injection. Soil profiles at the plots were taken after the campaign and again after six months in order to evaluate the transport and distribution of 2H within the unsaturated zone. Of 162 plant samples taken, 31 samples showed clear signals of artificially introduced 2H, of which all originate from the plots labeled up to 2 m depth. No artificially injected 2H was found in plants when tracer application occurred deeper than 2 m. Results further indicate a sharing of water resources between the investigated shrubs and trees in the upper 1 m whilst tree roots seem to have better access to deeper layers of the unsaturated zone. The soil profiles taken after six months reveal elevated 2H-concentrations from depths as great as 4 m up to 1 m below surface indicating upward transport of water vapor. Purely diffuse transport towards the soil surface yielded an estimated 0.4 mm over the dry season. Results are of particular significance for a more precise parameterization of SVAT models and the formulation of water balances in

  6. Design and laboratory testing of a chamber device to measure total flux of volatile organic compounds from the unsaturated zone under natural conditions

    NASA Astrophysics Data System (ADS)

    Tillman, Fred D.; Smith, James A.

    2004-11-01

    To determine if an aquifer contaminated with volatile organic compounds (VOCs) has potential for natural remediation, all natural processes affecting the fate and transport of VOCs in the subsurface must be identified and quantified. This research addresses the quantification of air-phase volatile organic compounds (VOCs) leaving the unsaturated zone soil gas and entering the atmosphere—including the additional flux provided by advective soil-gas movement induced by barometric pumping. A simple and easy-to-use device for measuring VOC flux under natural conditions is presented. The vertical flux chamber (VFC) was designed using numerical simulations and evaluated in the laboratory. Mass-balance numerical simulations based on continuously stirred tank reactor equations (CSTR) provided information on flux measurement performance of several sampling configurations with the final chamber configuration measuring greater than 96% of model-simulated fluxes. A laboratory device was constructed to evaluate the flux chamber under both diffusion-only and advection-plus-diffusion transport conditions. The flux chamber measured an average of 82% of 15 diffusion-only fluxes and an average of 95% of 15 additional advection-plus-diffusion flux experiments. The vertical flux chamber has the capability of providing reliable measurement of VOC flux from the unsaturated zone under both diffusion and advection transport conditions.

  7. Recent Improvements to the Unsaturated and Saturated Zone Flow and Transport Models for the Performance Assessment of the Yucca Mountain Repository in Nevada

    NASA Astrophysics Data System (ADS)

    Zhu, M.; Stein, J.; Houseworth, J.; Robinson, B.; Arnold, B.; Smistad, E.; Coleman, D.

    2008-12-01

    The U.S. Department of Energy has submitted a license application (LA) to the U.S. Nuclear Regulatory Commission (NRC) seeking authorization to construct the nation's first repository for spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. A key technical basis for the LA is the total system performance assessment model (TSPA) that estimates long-term behavior of both the natural system and the engineered system using a probabilistic approach. To support the TSPA for the LA, conceptual and numerical models for infiltration, unsaturated zone (UZ) flow, UZ transport, and saturated zone (SZ) flow and transport have been updated using new data and updated software. The most recent improvements in these model areas include: 1) a replacement of the infiltration model using the MASSIF (Mass Accounting System for Soil Infiltration and Flow) model; 2) the recalibration of the unsaturated flow model using new infiltration estimates, including the development of a methodology to integrate between the infiltration model and the UZ flow model through the weighting of the probability for different infiltration scenarios using the Generalized Likelihood Uncertainty Estimation method; 3) a recalculation of the UZ radionuclide transport breakthrough curves using updated UZ flow fields; and 4) a revised hydrogeologic framework (HFM2006) model based on new borehole data from the Nye County Early Warning Drilling Program, and the incorporation of HFM2006 into the SZ flow and transport models. This presentation will discuss the salient elements of these model updates and their incorporation into the TSPA-LA.

  8. Occurrence of soluble salts and moisture in the unsaturated zone and groundwater hydrochemistry along the middle and lower reaches of the Heihe River in northwest China

    NASA Astrophysics Data System (ADS)

    Zhou, Xun; Fang, Bin; Wan, Li; Cao, Wenbing; Wu, Shengjun; Feng, Weidong

    2006-08-01

    Deforestation, over-development of water resources and population growth have contributed to degeneration of vegetation in the Heihe River Basin in northwest China. Salts and water contents are the most important factors affecting the growth of vegetation in this arid area. This study was conducted to determine soluble salt levels of soils in the unsaturated zone and the hydrochemistry of groundwater at 14 sites in this region. Concentrations of soluble ions in the soils deceased with depth. Soil ion contents increased at depths below the root system of native plants. Sulfate was the dominant anion in both the unsaturated zone and the groundwater. Total dissolved solids (TDS) in groundwater ranged from less than 1 g/L in the middle reaches of the watershed to about 10 g/L in the arid lower reaches. In the middle and upper reaches of the watershed, salinity in soil and groundwater decreased. Groundwater was highly variable in hydrochemistry. The lower reaches was predominated by SO4-Na•Mg and SO4-Mg•Na type water, whereas in the middle reaches groundwater is characterized by lower TDS and HCO3-dominated type water. Evapotranspiration is responsible for occurrence of the soluble salts in the soil profiles. Dissolution is the dominant chemical process in the middle reaches, whereas evapotranspiration prevails in the lower reaches of the Heihe River.

  9. The Vadose Zone's Dynamic Response to a Natural Precipitation Event: Water Migration Through the Unsaturated Subsurface Monitored by GPR

    NASA Astrophysics Data System (ADS)

    Jacob, R. W.; Hermance, J. F.

    2005-05-01

    Water movement and its retentivity in the vadose zone is a fundamental link between precipitation, stormflow runoff and groundwater recharge. Moreover, the vertical distribution of water in the subsurface is fundamentally linked to vegetation since, following a precipitation event, the retentivity of near subsurface layers will determine the amount of water in the root zone. We report on a study of changes in the distribution of water in the subsurface during the hours and days following a precipitation event employing a sequence of high quality ground penetrating radar (GPR) measurements. The velocity of a radar signal in the subsurface is strongly modified by the soil water content (SWC), so that the technique provides an attractive means for non-invasively characterizing subsurface conditions using a Topp-like relation to infer SWC from GPR velocities. In this study, we focus on the vadose zone response to a natural precipitation event, by collecting a series of common mid-point (CMP) soundings at various times before, during, and after a 3 day period of rain at a geophysical test site in Southeastern New England. The shallow subsurface at the field site is unsaturated, and characterized to a depth of four meters by three layers: an organic rich soil layer (thickness = 0.9 m), a gravelly-sand layer (thickness = 2.9 m), underlain by a fine silty-sand, with bedrock at approximately 10 m deep. The CMPs were analyzed by carefully hand picking the first break of all observed phases: direct air, reflected, air refractions, and ground refracted phases. CMP soundings are ideal for this experiment allowing a combination of cross-checks. In particular, we have found it essential to complement the conventional analysis of reflected phases with the interpretation of ground refracted phases. Our study period involved a time of variable precipitation over 3 days, from July 23 to July 26, 2003, resulting in a total of 4.2 cm of water being added to the field site. The radar

  10. A steady state solution for ditch drainage problem with special reference to seepage face and unsaturated zone flow contribution: Derivation of a new drainage spacing eqaution

    NASA Astrophysics Data System (ADS)

    Yousfi, Ammar; Mechergui, Mohammed

    2016-04-01

    The seepage face is an important feature of the drainage process when recharge occurs to a permeable region with lateral outlets. Examples of the formation of a seepage face above the downstream water level include agricultural land drained by ditches. Flow problem to these drains has been investigated extensively by many researchers (e.g. Rubin, 1968; Hornberger et al. 1969; Verma and Brutsaert, 1970; Gureghian and Youngs, 1975; Vauclin et al., 1975; Skaggs and Tang, 1976; Youngs, 1990; Gureghian, 1981; Dere, 2000; Rushton and Youngs, 2010; Youngs, 2012; Castro-Orgaz et al., 2012) and may be tackled either using variably saturated flow models, or the complete 2-D solution of Laplace equation, or using the Dupuit-Forchheimer approximation; the most widely accepted methods to obtain analytical solutions for unconfined drainage problems. However, the investigation reported by Clement et al. (1996) suggest that accounting for the seepage face alone, as in the fully saturated flow model, does not improve the discharge estimate because of disregarding flow the unsaturated zone flow contribution. This assumption can induce errors in the location of the water table surface and results in an underestimation of the seepage face and the net discharge (e.g. Skaggs and Tang, 1976; Vauclin et al., 1979; Clement et al., 1996). The importance of the flow in the unsaturated zone has been highlighted by many authors on the basis of laboratory experiments and/or numerical experimentations (e.g. Rubin, 1968; Verma and Brutsaert, 1970; Todsen, 1973; Vauclin et al., 1979; Ahmad et al., 1993; Anguela, 2004; Luthin and Day, 1955; Shamsai and Narasimhan, 1991; Wise et al., 1994; Clement et al., 1996; Boufadel et al., 1999; Romano et al., 1999; Kao et al., 2001; Kao, 2002). These studies demonstrate the failure of fully saturated flow models and suggested that the error made when using these models not only depends on soil properties but also on the infiltration rate as reported by Kao et

  11. RHODIUM CATALYZED CONJUGATED ADDITION OF UNSATURATED CARBONYL COMPOUNDS BY TRIPHENYLBISMUTH IN AQUEOUS MEDIA AND UNDER AN AIR ATMOSPHERE. (R822668)

    EPA Science Inventory

    Abstract

    In the presence of a rhodium catalyst, small alpha, Greek,small beta, Greek-unsaturated est...

  12. COLLOID TRANSPORT IN UNSATURATED POROUS MEDIA: THE ROLE OF WATER CONTENT AND IONIC STRENGTH ON PARTICLE STRAINING

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Packed column and mathematical modeling studies were conducted to explore the influence of water content, pore-water ionic strength, and grain size on the transport of latex microsphere colloids (1 ƒÝm) in unsaturated conditions. Experiments were conducted under unfavorable conditions in terms of co...

  13. Mixing Cell Model: A One-Dimensional Numerical Model for Assessment of Water Flow and Contaminant Transport in the Unsaturated Zone

    SciTech Connect

    Arthur S. Rood

    2005-03-30

    This report describes the Mixing Cell Model code, a one-dimensional model for water flow and solute transport in the unsaturated zone under steady-state or transient flow conditions. The model is based on the principles and assumptions underlying mixing cell model formulations. The unsaturated zone is discretized into a series of independent mixing cells. Each cell may have unique hydrologic, lithologic, and sorptive properties. Ordinary differential equations describe the material (water and solute) balance within each cell. Water flow equations are derived from the continuity equation assuming that unit-gradient conditions exist at all times in each cell. Pressure gradients are considered implicitly through model discretization. Unsaturated hydraulic conductivity and moisture contents are determined by the material-specific moisture characteristic curves. Solute transport processes include explicit treatment of advective processes, first-order chain decay, and linear sorption reactions. Dispersion is addressed through implicit and explicit dispersion. Implicit dispersion is an inherent feature of all mixing cell models and originates from the formulation of the problem in terms of mass balance around fully mixed volume elements. Expressions are provided that relate implicit dispersion to the physical dispersion of the system. Two FORTRAN codes were developed to solve the water flow and solute transport equations: (1) the Mixing-Cell Model for Flow (MCMF) solves transient water flow problems and (2) the Mixing Cell Model for Transport (MCMT) solves the solute transport problem. The transient water flow problem is typically solved first by estimating the water flux through each cell in the model domain as a function of time using the MCMF code. These data are stored in either ASCII or binary files that are later read by the solute transport code (MCMT). Code output includes solute pore water concentrations, water and solute inventories in each cell and at each

  14. Mixing Cell Model: A One-Dimensional Numerical Model for Assessment of Water Flow and Contaminant Transport in the Unsaturated Zone

    SciTech Connect

    A. S. Rood

    2005-03-01

    This report describes the Mixing Cell Model code, a one-dimensional model for water flow and solute transport in the unsaturated zone under steady-state or transient flow conditions. The model is based on the principles and assumptions underlying mixing cell model formulations. The unsaturated zone is discretized into a series of independent mixing cells. Each cell may have unique hydrologic, lithologic, and sorptive properties. Ordinary differential equations describe the material (water and solute) balance within each cell. Water flow equations are derived from the continuity equation assuming that unit-gradient conditions exist at all times in each cell. Pressure gradients are considered implicitly through model discretization. Unsaturated hydraulic conductivity and moisture contents are determined by the material-specific moisture characteristic curves. Solute transport processes include explicit treatment of advective processes, first-order chain decay, and linear sorption reactions. Dispersion is addressed through implicit and explicit dispersion. Implicit dispersion is an inherent feature of all mixing cell models and originates from the formulation of the problem in terms of mass balance around fully mixed volume elements. Expressions are provided that relate implicit dispersion to the physical dispersion of the system. Two FORTRAN codes were developed to solve the water flow and solute transport equations: (1) the Mixing-Cell Model for Flow (MCMF) solves transient water flow problems and (2) the Mixing Cell Model for Transport (MCMT) solves the solute transport problem. The transient water flow problem is typically solved first by estimating the water flux through each cell in the model domain as a function of time using the MCMF code. These data are stored in either ASCII or binary files that are later read by the solute transport code (MCMT). Code output includes solute pore water concentrations, water and solute inventories in each cell and at each

  15. Mixing Cell Model: A One-Dimensional Numerical Model for Assessment of Water Flow and Contaminant Transport in the Unsaturated Zone

    SciTech Connect

    A. S. Rood

    2009-04-01

    This report describes the Mixing Cell Model code, a one-dimensional model for water flow and solute transport in the unsaturated zone under steady-state or transient flow conditions. The model is based on the principles and assumptions underlying mixing cell model formulations. The unsaturated zone is discretized into a series of independent mixing cells. Each cell may have unique hydrologic, lithologic, and sorptive properties. Ordinary differential equations describe the material (water and solute) balance within each cell. Water flow equations are derived from the continuity equation assuming that unit-gradient conditions exist at all times in each cell. Pressure gradients are considered implicitly through model discretization. Unsaturated hydraulic conductivity and moisture contents are determined by the material-specific moisture characteristic curves. Solute transport processes include explicit treatment of advective processes, first-order chain decay, and linear sorption reactions. Dispersion is addressed through implicit and explicit dispersion. Implicit dispersion is an inherent feature of all mixing cell models and originates from the formulation of the problem in terms of mass balance around fully mixed volume elements. Expressions are provided that relate implicit dispersion to the physical dispersion of the system. Two FORTRAN codes were developed to solve the water flow and solute transport equations: (1) the Mixing-Cell Model for Flow (MCMF) solves transient water flow problems and (2) the Mixing Cell Model for Transport (MCMT) solves the solute transport problem. The transient water flow problem is typically solved first by estimating the water flux through each cell in the model domain as a function of time using the MCMF code. These data are stored in either ASCII or binary files that are later read by the solute transport code (MCMT). Code output includes solute pore water concentrations, water and solute inventories in each cell and at each

  16. Mixing Cell Model: A One-Dimensional Numerical Model for Assessment of Water Flow and Contaminant Transport in the Unsaturated Zone

    SciTech Connect

    A. S. Rood

    2010-10-01

    This report describes the Mixing Cell Model code, a one-dimensional model for water flow and solute transport in the unsaturated zone under steady-state or transient flow conditions. The model is based on the principles and assumptions underlying mixing cell model formulations. The unsaturated zone is discretized into a series of independent mixing cells. Each cell may have unique hydrologic, lithologic, and sorptive properties. Ordinary differential equations describe the material (water and solute) balance within each cell. Water flow equations are derived from the continuity equation assuming that unit-gradient conditions exist at all times in each cell. Pressure gradients are considered implicitly through model discretization. Unsaturated hydraulic conductivity and moisture contents are determined by the material-specific moisture characteristic curves. Solute transport processes include explicit treatment of advective processes, first-order chain decay, and linear sorption reactions. Dispersion is addressed through implicit and explicit dispersion. Implicit dispersion is an inherent feature of all mixing cell models and originates from the formulation of the problem in terms of mass balance around fully mixed volume elements. Expressions are provided that relate implicit dispersion to the physical dispersion of the system. Two FORTRAN codes were developed to solve the water flow and solute transport equations: (1) the Mixing-Cell Model for Flow (MCMF) solves transient water flow problems and (2) the Mixing Cell Model for Transport (MCMT) solves the solute transport problem. The transient water flow problem is typically solved first by estimating the water flux through each cell in the model domain as a function of time using the MCMF code. These data are stored in either ASCII or binary files that are later read by the solute transport code (MCMT). Code output includes solute pore water concentrations, water and solute inventories in each cell and at each

  17. Spatial and temporal variability of nitrate and nitrous oxide concentrations in the unsaturated zone at a corn field in the US Midwest

    NASA Astrophysics Data System (ADS)

    Gopalakrishnan, G.; Negri, C.

    2011-12-01

    There has been a significant increase in reactive nitrogen in the environment as a result of human activity. Reactive nitrogen of anthropogenic origin now equals that derived from natural terrestrial nitrogen fixation and is expected to exceed it by the end of the decade. Nitrogen is applied to crops as fertilizer and impacts the environment through water quality impairments (mostly as nitrate) and as greenhouse gas emissions (as nitrous oxide). Research on environmental impacts resulting from nitrogen application in the form of fertilizers has focused disproportionately on the degradation of water quality from agricultural non-point sources. The impacts of this degradation are registered both locally, with runoff and percolation of agrochemicals into local surface water and groundwater, and on a larger scale, such as the increase in the anoxic zone in the Gulf of Mexico attributed to nitrate from the Mississippi River. Impacts to the global climate from increased production of nitrous oxide as a result of increased fertilization are equally significant. Nitrous oxide is a greenhouse gas with a warming potential that is approximately 300 times greater than carbon dioxide. Direct emissions of nitrous oxide from the soil have been expressed as 1% of the applied nitrogen. Indirect emissions due to runoff, leaching and volatilization of the nitrogen from the field have been expressed as 0.75% of the applied nitrogen. Many studies have focused on processes governing nitrogen fluxes in the soil, surface water and groundwater systems. However, research on the biogeochemical processes regulating nitrogen fluxes in the unsaturated zone and consequent impacts on nitrate and nitrous oxide concentrations in groundwater are lacking. Our study explores the spatial and temporal variability of nitrate and nitrous oxide concentrations in the vadose zone at a 15 acre corn field in the US Midwest and links it to the concentrations found in the groundwater at the field site. Results

  18. Using Concentrations and Isotopic Compositions of CO2 to Distinguish Microbial Production of CO2 in Unsaturated Zone Sediments in Hydrogeochemical Models

    NASA Astrophysics Data System (ADS)

    Conrad, M. E.; Arora, B.; Williams, K. H.; Bill, M.; Spycher, N.; Steefel, C. I.; Tokunaga, T. K.; Hubbard, S. S.

    2014-12-01

    Quantifying levels of microbial activity in unsaturated subsurface environments is an important factor for understanding exchange of greenhouse gases (e.g., CO2, CH4, N2O) with the atmosphere. For CO2, this is problematic due the variety of processes affecting its sources, fate and transport in the vadose zone (e.g., root respiration, carbonate dissolution and precipitation, exchange with pore water/groundwater and microbial production and consumption). To determine the impacts of all these processes and dependence on variables including temperature, moisture content and pH requires coupled numerical models supported by robust, long-term data sets. We are attempting to do this for a small (~90,000 m2) floodplain adjacent to the Colorado River in the town of Rifle, Colorado. The geology of the site consists of 6-8 m of Quaternary alluvium composed of quartz and feldspar sands with silts, clays, pebbles, and cobbles overlying the less permeable Tertiary Wasatch Formation. The unsaturated zone is 3-4 m thick overlying a perched aquifer above the alluvium-Wasatch contact. Depth-distributed gas samplers and suction lysimeters for pore water sampling were installed at three locations across the site in March of 2013. From April 2013 to present, soil gas samples have been collected on a bi-weekly to monthly interval and analyzed for gas concentrations and isotopic compositions. Through the first year, several significant spatial and temporal trends have emerged from the data including higher soil gas CO2 (up to 6% near the water table) with higher δ13C values during the warmer summer months, possibly signifying higher levels of microbial activity. In the shallower soils, CO2 concentrations are lower (atmospheric to 2%) with more variable δ13C values (ranging from -18‰ in the summer to -24‰ in the winter) likely due to slower exchange with the atmosphere during the winter when surface soils are more saturated due to snow cover and melting. Extensive data has also

  19. How spatial variations of chalk groundwater geochemistry are related to superficial formations and infiltration processes of unsaturated zone (quarry of Saint Martin le Noeud, France)

    NASA Astrophysics Data System (ADS)

    Barhoum, Sarah; Valdès-Lao, Danièle; Guérin, Roger; Gombert, Philippe

    2013-04-01

    Chalk is complex because of its dual porosity and because of superficial layers more or less thick and more or less permeable. Furthermore there is few knowledge in understanding of groundwater infiltration and dissolution processes in the chalk unsaturated zone (UZ). The role of superficial formations has to be studied especially. The experimental site is an ancient underground quarry of chalk which extends over 1200 m long and 150 m wide (30 m depth) in Saint Martin le Noeud, south of Beauvais, France. This quarry is particularly interesting to study infiltration and dissolution processes indeed this site allows to access to the interface between the unsaturated zone and the saturated zone. Water percolates from the top of the quarry more or less depending on the season. Water table outcrops in the cave and makes about 20 underground lakes. Above the quarry chalk is covered clay-with-flints (CWF) and loess, in surface there are cultivated crops fields. On the first year of the study, physicochemical parameters: temperature, depth, pH, conductivity were recorded in seven lakes with high frequency (every hour). During the same period we sampled the 20 lakes water every month to measure major ions. During this sampling period, percolation was not sufficient to collect percolated water. Results of underground GPS, electric resistivity tomography and observations of three borehole showed that thickness unsaturated zone and that the thicknesses of the superficial formations vary a lot spatially. Three interesting points (separated by less than 1 km) are presented: the above the Pedro lake (25 m of UZ, a few cm of CWF), above the Stalactites lake (30 m of UZ, more than 2.40 m of CWF); above the Blue lake (35 m depth, 60 cm of CWF). First results of chemistry showed that the temporal variation is very low during the first year but there spatial variation is very important at quarry scale. The geochemistry of the lakes are very different: HCO3- varies from 100 to 250mg

  20. An evaluation of materials and methods for vapour measurement of the isotopic composition of pore water in deep, unsaturated zones.

    PubMed

    Pratt, Dyan L; Lu, Mengna; Lee Barbour, S; Jim Hendry, M

    2016-01-01

    The development of in situ vapour sampling methods to measure δ(2)H and δ(18)O in pore water of deep, unsaturated soil profiles, including mine tailings and waste rock, is required to improve our ability to track water migration through these deposits. To develop appropriate field sampling methods, a laboratory study was first undertaken to evaluate potential materials and sampling methods to collect and analyse vapour samples from unsaturated mine waste. Field methods were developed based on these findings and tested at two mine sites using either on-site analyses with a portable isotope laser spectrometer or sample collection and storage prior to laboratory analyses. The field sites included a series of deep (>50 m) multiport profiles within a coal waste rock dump and open wells installed in a sand tailings dyke at an oil sands mine. Laboratory results show that memory effects in sample bags and tubing require 3-5 pore volumes of vapour flushing prior to sample collection and sample storage times are limited to 24 h. Field sampling highlighted a number of challenges including the need to correct for sample humidity and in situ temperature. Best results were obtained when a portable laser spectrometer was used to measure vapour samples in situ. PMID:27002493

  1. Inventories and mobilization of unsaturated zone sulfate, fluoride, and chloride related to land use change in semiarid regions, southwestern United States and Australia

    NASA Astrophysics Data System (ADS)

    Scanlon, Bridget R.; Stonestrom, David A.; Reedy, Robert C.; Leaney, Fred W.; Gates, John; Cresswell, Richard G.

    2009-07-01

    Unsaturated zone salt reservoirs are potentially mobilized by increased groundwater recharge as semiarid lands are cultivated. This study explores the amounts of pore water sulfate and fluoride relative to chloride in unsaturated zone profiles, evaluates their sources, estimates mobilization due to past land use change, and assesses the impacts on groundwater quality. Inventories of water-extractable chloride, sulfate, and fluoride were determined from borehole samples of soils and sediments collected beneath natural ecosystems (N = 4), nonirrigated ("rain-fed") croplands (N = 18), and irrigated croplands (N = 6) in the southwestern United States and in the Murray Basin, Australia. Natural ecosystems contain generally large sulfate inventories (7800-120,000 kg/ha) and lower fluoride inventories (630-3900 kg/ha) relative to chloride inventories (6600-41,000 kg/ha). Order-of-magnitude higher chloride concentrations in precipitation and generally longer accumulation times result in much larger chloride inventories in the Murray Basin than in the southwestern United States. Atmospheric deposition during the current dry interglacial climatic regime accounts for most of the measured sulfate in both U.S. and Australian regions. Fluoride inventories are greater than can be accounted for by atmospheric deposition in most cases, suggesting that fluoride may accumulate across glacial/interglacial climatic cycles. Chemical modeling indicates that fluorite controls fluoride mobility and suggests that water-extractable fluoride may include some fluoride from mineral dissolution. Increased groundwater drainage/recharge following land use change readily mobilized chloride. Sulfate displacement fronts matched or lagged chloride fronts by up to 4 m. In contrast, fluoride mobilization was minimal in all regions. Understanding linkages between salt inventories, increased recharge, and groundwater quality is important for quantifying impacts of anthropogenic activities on groundwater

  2. Inventories and mobilization of unsaturated zone sulfate, fluoride, and chloride related to land use change in semiarid regions, southwestern United States and Australia

    USGS Publications Warehouse

    Scanlon, B.R.; Stonestrom, D.A.; Reedy, R.C.; Leaney, F.W.; Gates, J.; Cresswell, R.G.

    2009-01-01

    Unsaturated zone salt reservoirs are potentially mobilized by increased groundwater recharge as semiarid lands are cultivated. This study explores the amounts of pore water sulfate and fluoride relative to chloride in unsaturated zone profiles, evaluates their sources, estimates mobilization due to past land use change, and assesses the impacts on groundwater quality. Inventories of water-extractable chloride, sulfate, and fluoride were determined from borehole samples of soils and sediments collected beneath natural ecosystems (N = 4), nonirrigated ("rain-fed") croplands (N = 18), and irrigated croplands (N = 6) in the southwestern United States and in the Murray Basin, Australia. Natural ecosystems contain generally large sulfate inventories (7800-120,000 kg/ha) and lower fluoride inventories (630-3900 kg/ha) relative to chloride inventories (6600-41,000 kg/ha). Order-of-magnitude higher chloride concentrations in precipitation and generally longer accumulation times result in much larger chloride inventories in the Murray Basin than in the southwestern United States. Atmospheric deposition during the current dry interglacial climatic regime accounts for most of the measured sulfate in both U.S. and Australian regions. Fluoride inventories are greater than can be accounted for by atmospheric deposition in most cases, suggesting that fluoride may accumulate across glacial/ interglacial climatic cycles. Chemical modeling indicates that fluorite controls fluoride mobility and suggests that water-extractable fluoride may include some fluoride from mineral dissolution. Increased groundwater drainage/recharge following land use change readily mobilized chloride. Sulfate displacement fronts matched or lagged chloride fronts by up to 4 m. In contrast, fluoride mobilization was minimal in all regions. Understanding linkages between salt inventories, increased recharge, and groundwater quality is important for quantifying impacts of anthropogenic activities on groundwater

  3. Annual report on monitoring of the unsaturated zone and recharge areas at INEL to the state of Idaho INLEL Oversight COmmittee. Draft

    SciTech Connect

    Horn, D.; Liou, J.; Finnie, J.

    1993-03-01

    This project, begun in March 1991, was originally structured as two separate research efforts: An investigation of the recharge phenomenon and surface water-ground water interactions at the INEL; and a study of water and contaminant movement through the unsaturated zone, including a review of computer models used to described this process. During the initial months of work, it became obvious to those involved in these studies that the two topic areas were intimately related, and work since that time has proceeded with no firm boundaries between the two efforts. Much of the Phase I work (March 1991--March 1992) consisted of a detailed review of available literature pertinent to the two research topics and to the INEL site. This Annual Report summarizes the other project activities during Phase III, and is organized into three sections: Section I -- an overview of the ongoing efforts related to computer model algorithms and data requirements for modeling the transport process in the unsaturated zone (Dr. Jim Liou). Section H -- a review of ongoing work to predict the growth and decay of the ground water mound beneath the INEL spreading basins, using the computer model UNSAT-2 (Dr. John Finnie). Section M -- a final report of the completed study effort examining the recharge rates associated with stream flow in the Big Lost River, and the effects of this recharge on ground water levels at the INEL site (Dr. Dennis Horn). Phase M of the project has now begun, and will conclude in December 1993 with two final reports documenting the work that has been briefly described in Sections I and H of this report.

  4. Annual report on monitoring of the unsaturated zone and recharge areas at INEL to the state of Idaho INLEL Oversight COmmittee

    SciTech Connect

    Horn, D.; Liou, J.; Finnie, J.

    1993-03-01

    This project, begun in March 1991, was originally structured as two separate research efforts: An investigation of the recharge phenomenon and surface water-ground water interactions at the INEL; and a study of water and contaminant movement through the unsaturated zone, including a review of computer models used to described this process. During the initial months of work, it became obvious to those involved in these studies that the two topic areas were intimately related, and work since that time has proceeded with no firm boundaries between the two efforts. Much of the Phase I work (March 1991--March 1992) consisted of a detailed review of available literature pertinent to the two research topics and to the INEL site. This Annual Report summarizes the other project activities during Phase III, and is organized into three sections: Section I -- an overview of the ongoing efforts related to computer model algorithms and data requirements for modeling the transport process in the unsaturated zone (Dr. Jim Liou). Section H -- a review of ongoing work to predict the growth and decay of the ground water mound beneath the INEL spreading basins, using the computer model UNSAT-2 (Dr. John Finnie). Section M -- a final report of the completed study effort examining the recharge rates associated with stream flow in the Big Lost River, and the effects of this recharge on ground water levels at the INEL site (Dr. Dennis Horn). Phase M of the project has now begun, and will conclude in December 1993 with two final reports documenting the work that has been briefly described in Sections I and H of this report.

  5. Implications of surfactant-induced flow for miscible-displacement estimation of air-water interfacial areas in unsaturated porous media.

    PubMed

    Costanza-Robinson, Molly S; Zheng, Zheng; Henry, Eric J; Estabrook, Benjamin D; Littlefield, Malcolm H

    2012-10-16

    Surfactant miscible-displacement experiments represent a conventional means of estimating air-water interfacial area (A(I)) in unsaturated porous media. However, changes in surface tension during the experiment can potentially induce unsaturated flow, thereby altering interfacial areas and violating several fundamental method assumptions, including that of steady-state flow. In this work, the magnitude of surfactant-induced flow was quantified by monitoring moisture content and perturbations to effluent flow rate during miscible-displacement experiments conducted using a range of surfactant concentrations. For systems initially at 83% moisture saturation (S(W)), decreases of 18-43% S(W) occurred following surfactant introduction, with the magnitude and rate of drainage inversely related to the surface tension of the surfactant solution. Drainage induced by 0.1 mM sodium dodecyl benzene sulfonate, commonly used for A(I) estimation, resulted in effluent flow rate increases of up to 27% above steady-state conditions and is estimated to more than double the interfacial area over the course of the experiment. Depending on the surfactant concentration and the moisture content used to describe the system, A(I) estimates varied more than 3-fold. The magnitude of surfactant-induced flow is considerably larger than previously recognized and casts doubt on the reliability of A(I) estimation by surfactant miscible-displacement. PMID:23033988

  6. Movement of water through the thick unsaturated zone underlying Oro Grande and Sheep Creek Washes in the western Mojave Desert, USA

    USGS Publications Warehouse

    Izbicki, J.A.; Radyk, J.; Michel, R.L.

    2002-01-01

    Previous studies indicate that a small quantity of recharge occurs from infiltration of streamflow in intermittent streams in the upper Mojave River basin, in the western Mojave Desert, near Victorville, California. Chloride, tritium, and stable isotope data collected in the unsaturated zone between 1994 and 1998 from boreholes drilled in Oro Grande and Sheep Creek Washes indicate that infiltration of streamflow occurs to depths below the root zone, and presumably to the water table, along much of Oro Grande Wash and near the mountain front along Sheep Creek Wash. Differences in infiltration at sites along each wash are the result of hydrologic variables such as proximity to the mountain front, quantity of streamflow, and texture of the subsurface deposits. Differences in infiltration between the washes are the result of large-scale geomorphic processes. For example, Oro Grande wash is incised into the Victorville fan and infiltration has occurred at approximately the same location over recent geologic time. In contrast, Sheep Creek Wash overlies an active alluvial fan and the stream channel can move across the fan surface through time. Infiltration does not occur to depths below the root zone at control sites outside of the washes.

  7. Linear thermal expansion data for tuffs from the unsaturated zone at Yucca Mountain, Nevada; Yucca Mountain Site Characterization Project

    SciTech Connect

    Schwartz, B.M.; Chocas, C.S.

    1992-07-01

    Experiment results are presented for linear thermal expansion measurements on tuffaceous rocks from the unsaturated

  8. Methodology to evaluate the effect of sorption in the unsaturated zone on the storage of nitrate and other ions and their transport across the water table, southern New Jersey

    USGS Publications Warehouse

    Reilly, Timothy J.; Baehr, Arthur L.

    2006-01-01

    A new field-based approach for determining sorption in the unsaturated zone and its effect on the storage of ions and their transport in recharge to ground water has been demonstrated for a small agricultural watershed in the Coastal Plain of southern New Jersey. Moisture-content and chemical-concentration data obtained from unsaturated-zone-core and shallow-ground-water samples were used to estimate the mass flux of chemical constituents across the water table, as well as sorption coefficients (Kd). The selectivity order of the Kd values for cations is consistent with the expected selectivity order: for example, Na+ > Mg++ > Ca++ for sands. Although calculated sorption coefficients, as expected, were greater for cations than for anions, sorption had a substantial effect on the transport of anions through the unsaturated zone; in particular, average Kd values for NO3- were 0.22 liters per milligram for sands and 0.62 liters per milligram for finer grained sediments. The unsaturated zone in the study area is a large reservoir for nitrogen. Models that do not account for sorption are likely to result in unrealistic predictions of contaminant transport rate and provide overly optimistic expectations for natural cleansing in this watershed and those in other similar hydrogeologic settings.

  9. The impact of relict organic materials on the denitrification capacity in the unsaturated-saturated zone continuum of three volcanic profiles.

    PubMed

    Clague, J C; Stenger, R; Clough, T J

    2013-01-01

    The denitrification capacity of wetlands, riparian zones, and aquifers in glacial outwash areas is well documented, but little or no information exists for volcanic profiles, particularly those containing relict organic matter contained in or on top of paleosols (old soils buried by volcanic deposits) below the groundwater table. Relict carbon contained in these layers could provide the necessary electrons to fuel heterotrophic denitrification. To the best of our knowledge, this is the first study investigating the denitrification capacity in both the unsaturated and saturated zone of volcanic profiles. Samples from three profile types with differing organic matter distribution were amended with N-enriched nitrate (NO-) and incubated in the laboratory under anaerobic conditions. Dinitrogen (N) dominated the N gas fluxes; averaged across all samples, it accounted for 96% of the total N (nitrous oxide [NO] and N) gas fluxes. Dinitrogen fluxes were generally highest in the A horizon samples (4.1-6.2 nmol N g h), but substantial fluxes were also observed in some paleosol layers (up to 0.72 nmol N g h). A significant correlation ( < 0.001) was found between the concentration of extractable dissolved organic carbon and the total N gas flux produced in samples from below the A horizon, suggesting that heterotrophic denitrification was the dominant NO attenuation process in this study. Extrapolation of lab-derived denitrification capacities to field conditions suggests that the denitrification capacity of profiles containing relict soil organic matter in the saturated zone exceeds the estimated N leaching from the root zone. PMID:23673749

  10. Combining steam injection with hydraulic fracturing for the in situ remediation of the unsaturated zone of a fractured soil polluted by jet fuel.

    PubMed

    Nilsson, Bertel; Tzovolou, Dimitra; Jeczalik, Maciej; Kasela, Tomasz; Slack, William; Klint, Knud E; Haeseler, Frank; Tsakiroglou, Christos D

    2011-03-01

    A steam injection pilot-scale experiment was performed on the unsaturated zone of a strongly heterogeneous fractured soil contaminated by jet fuel. Before the treatment, the soil was stimulated by creating sub-horizontal sand-filled hydraulic fractures at three depths. The steam was injected through one hydraulic fracture and gas/water/non-aqueous phase liquid (NAPL) was extracted from the remaining fractures by applying a vacuum to extraction wells. The injection strategy was designed to maximize the heat delivery over the entire cell (10 m × 10 m × 5 m). The soil temperature profile, the recovered NAPL, the extracted water, and the concentrations of volatile organic compounds (VOCs) in the gas phase were monitored during the field test. GC-MS chemical analyses of pre- and post-treatment soil samples allowed for the quantitative assessment of the remediation efficiency. The growth of the heat front followed the configuration of hydraulic fractures. The average concentration of total hydrocarbons (g/kg of soil) was reduced by ∼ 43% in the upper target zone (depth = 1.5-3.9 m) and by ∼ 72% over the entire zone (depth = 1.5-5.5 m). The total NAPL mass removal based on gas and liquid stream measurements and the free-NAPL product were almost 30% and 2%, respectively, of those estimated from chemical analyses of pre- and post-treatment soil samples. The dominant mechanisms of soil remediation was the vaporization of jet fuel compounds at temperatures lower than their normal boiling points (steam distillation) enhanced by the ventilation of porous matrix due to the forced convective flow of air. In addition, the significant reduction of the NAPL mass in the less-heated deeper zone may be attributed to the counter-current imbibition of condensed water from natural fractures into the porous matrix and the gravity drainage associated with seasonal fluctuations of the water table. PMID:21030134

  11. CO2 production rate maxima in the deeper unsaturated zone of a semi-arid floodplain at Rifle, Colorado

    NASA Astrophysics Data System (ADS)

    Tokunaga, T. K.; Kim, Y.; Wan, J.; Dong, W.; Conrad, M. E.; Bill, M.; Hobson, C.; Williams, K. H.; Long, P. E.

    2015-12-01

    Fluxes of CO2 from soils are important to understand in order to predict subsurface feedbacks to the atmosphere and responses to climate change. Such fluxes are commonly monitored at the soil surface and generally assumed to largely originate within shallow depths. Relatively little is understood on the depth distribution of CO2 production below the rhizosphere. We monitored CO2 fluxes at the soil surface, and measured vertical profiles of vadose CO2 concentrations, matric potentials, and temperatures at the Rifle Site, a saline semi-arid floodplain along the Colorado River in order to determine the significance of deeper vadose zone respiration. Vadose zone CO2 profiles exhibit temperature-dependent seasonal variations, and are consistent with CO2 fluxes measured at the soil surface. The measured vadose zone CO2 concentration profiles combined with gas diffusion coefficients estimated from soil properties indicated that local maxima in rates of CO2 production persist in the deeper vadose zone, about 1 m below the rhizosphere, and above the water table (~3.5 m below the soil surface). We hypothesized that water and oxygen activities, nutrient levels, and temperatures remain favorable for microbial respiration throughout the year in the subrhizosphere, unlike overlying drier soils and the underlying poorly aerated aquifer. Using soils and sediments from the field site, the hypothesized existence of deeper subsurface maxima in CO2 production rate is currently being tested in the laboratory through sediment incubation experiments and in 2.0 m tall vadose zone columns. Initial results from the laboratory support the hypothesized persistence of a subrhizosphere "hot zone" for microbial respiration, partly sustained through seasonal pulses of dissolved and labile organic carbon originating from the rhizosphere. These findings suggest that similar sustained deeper local maxima in respiration rates may occur in many other regions where near-surface conditions are

  12. Dynamic effects during alternate infiltration and drainage of unsaturated granular media studied using the Lattice Boltzmann Method

    NASA Astrophysics Data System (ADS)

    Galindo-Torres, S.; Scheuermann, A.; Pedroso, D.; Li, L.; Williams, D.; Golder Geomechanics Centre

    2011-12-01

    Dynamic effects in connection with multi-phase or unsaturated water flow in soils are often observed experimentally. They generally arise as temporarily delayed changes in the water content or in the outflow. Possible mechanisms leading to such effects during infiltration have not been investigated in detail. Experimental investigations on sand columns have shown that for cyclic hydraulic conditions, i.e. the alternate infiltration and drainage of water, dynamic effects may even result in an accumulation of water within the pore structure, which is denoted here as hydraulic ratcheting. This cyclic accumulation of water may lead to catastrophic consequences due to the associated increase in pore water pressure. Although this hypothesis is supported by experimental evidence, a microscopic insight into the underlying processes and mechanisms is needed in order to predict it. In this study, numerical simulations based on the Lattice Boltzmann Method (LBM) are conducted to examine these microscopic effects that are beyond the scope of traditional models. In the LBM, the fluid is represented by a discrete mesh used to solve the fundamental Boltzmann equation. By adding cohesive and repulsive body forces into the LBM mesh, multi-component and multi-phase fluids and capillarity interaction with solids can be realistically represented. With this tool, a fully interacting unsaturated soil, composed of three phases: solid particles, water and air, is modelled as shown in Figure 1. The air and water interact by forming bubbles, and capillarity bridges are formed around closely-packed particles. By harmonically changing the pressure conditions on the bottom boundary, the cyclic behaviour related to the hydraulic ratcheting is simulated. Extensive simulations of random configurations explore the effects of the soil geometric features (particle size distribution, mean constriction size and porosity) and the frequency of infiltration on the cyclic water accumulation. The results

  13. Stratigraphy of the unsaturated zone and uppermost part of the Snake River Plain aquifer at test area north, Idaho National Engineering Laboratory, Idaho

    SciTech Connect

    Anderson, S.R.; Bowers, B.

    1995-06-01

    A complex sequence of basalt flows and sedimentary interbeds underlies Test Area North (TAN) at the Idaho National Engineering Laboratory in eastern Idaho. Wells drilled to depths of at least 500 feet penetrate 10 basalt-flow groups and 5 to 10 sedimentary interbeds that range in age from about 940,000 to 1.4 million years. Each basalt-flow group consists of one or more basalt flows from a brief, single or compound eruption. All basalt flows of each group erupted from the same vent, and have similar ages, paleomagnetic properties, potassium contents, and natural-gamma emissions. Sedimentary interbeds consist of fluvial, lacustrine, and eolian deposits of clay, silt, sand, and gravel that accumulated for hundreds to hundreds of thousands of years during periods of volcanic quiescence. Basalt and sediment are elevated by hundreds of feet with respect to rocks of equivalent age south and cast of the area, a relation that is attributed to past uplift at TAN. Basalt and sediment are unsaturated to a depth of about 200 feet below land surface. Rocks below this depth are saturated and make up the Snake River Plain aquifer. The effective base of the aquifer is at a depth of 885 feet below land surface. Detailed stratigraphic relations for the lowermost part of the aquifer in the depth interval from 500 to 885 feet were not determined because of insufficient data. The stratigraphy of basalt-flow groups and sedimentary interbeds in the upper 500 feet of the unsaturated zone and aquifer was determined from natural-gamma logs, lithologic logs, and well cores. Basalt cores were evaluated for potassium-argon ages, paleomagnetic properties, petrographic characteristics, and chemical composition. Stratigraphic control was provided by differences in ages, paleomagnetic properties, potassium content, and natural-gamma emissions of basalt-flow groups and sedimentary interbeds.

  14. Multiphase Reactive Transport modeling of Stable Isotope Fractionation of Infiltrating Unsaturated Zone Pore Water and Vapor Using TOUGHREACT

    SciTech Connect

    Singleton, Michael J.; Sonnenthal, Eric L.; Conrad, Mark E.; DePaolo, Donald J.

    2003-08-28

    Numerical simulations of transport and isotope fractionation provide a method to quantitatively interpret vadose zone pore water stable isotope depth profiles based on soil properties, climatic conditions, and infiltration. We incorporate the temperature-dependent equilibration of stable isotopic species between water and water vapor, and their differing diffusive transport properties into the thermodynamic database of the reactive transport code TOUGHREACT. These simulations are used to illustrate the evolution of stable isotope profiles in semiarid regions where recharge during wet seasons disturbs the drying profile traditionally associated with vadose zone pore waters. Alternating wet and dry seasons lead to annual fluctuations in moisture content, capillary pressure, and stable isotope compositions in the vadose zone. Periodic infiltration models capture the effects of seasonal increases in precipitation and predict stable isotope profiles that are distinct from those observed under drying (zero infiltration) conditions. After infiltration, evaporation causes a shift to higher 18O and D values, which are preserved in the deeper pore waters. The magnitude of the isotopic composition shift preserved in deep vadose zone pore waters varies inversely with the rate of infiltration.

  15. Hydrogeologic setting and simulation of pesticide fate and transport in the unsaturated zone of a regolith-mantled, carbonate-rock terrain near Newville, Pennsylvania

    USGS Publications Warehouse

    Hippe, D.J.; Hall, D.W.

    1996-01-01

    Physical and chemical data were collected from May 1991 through April 1993 at a 4.5 hectare field site in Cumberland County, Pa., about 5 kilometers southeast of Newville. These data were used to define the hydrogeologic setting of a field site representative of the intensively farmed carbonate valleys of southeastern and south-central Pennsylvania. The environmental processing of commonly used pesticides (herbicides, fungicides, and insecticides) in the unsaturated zone was simulated with a process- oriented digital model to evaluate the environmental fate and transport of pesticides to ground water. Site data and modelling results provide a basis for a discussion of water-quality implications of agricultural best-management practices. The carbonate valleys of Pennsylvania comprise regolith-mantled carbonate-rock terrains that consist of broad undulating upland areas dissected by mostly dry valleys and widely spaced spring-fed creeks. The upland areas are farmed and exhibit possess a doline karst topography with many closed depressions, sinkholes, and bedrock outcrops. Unsaturated materials at the field site consist of an almost continuous soil cover composed of fine-grained residuum underlain by an intermediate vadose zone composed of karstified limestone. Soils are absent on scattered bedrock outcrops and are more than 12 meters thick in other areas of the site. The soil profile stores appreciable quantities of water with a volumetric average of about 36 percent water at field capacity. Organic carbon content of soil materials is about 1.7 percent in the Ap-horizon and from 0.1 to 0.3 percent throughout the full thickness of the B- and C-horizons. Atrazine, metolachlor, simazine, and the atrazine soil metabolites deethylatrazine and deisopropylatrazine were detected at concentrations above 0.05 mg/L in just the upper 0.6 meters of soil materials. However, detectable concentrations of atrazine, simazine, and atrazine soil metabolites were measured in water

  16. Influence of surface passivation and water content on mineral reactions in unsaturated porous media: Implications for brucite carbonation and CO2 sequestration

    NASA Astrophysics Data System (ADS)

    Harrison, Anna L.; Dipple, Gregory M.; Power, Ian M.; Mayer, K. Ulrich

    2015-01-01

    The evolution of mineral reactive surface area is an important control on the progress of carbon mineralization reactions that sequester anthropogenic CO2. Dry conditions in unsaturated porous media and the passivation of reactive surface area by secondary phase precipitation complicate predictions of reactive surface during carbon mineralization reactions. Unsaturated brucite [Mg(OH)2] bearing column experiments were used to evaluate the effects of water saturation and hydrous Mg-carbonate precipitation on reaction of brucite with 10% CO2 gas streams at ambient conditions. We demonstrate that a lack of available water severely limits reaction progress largely due to the requirement of water as a reactant to form hydrated Mg-carbonates. The precipitation of a poorly crystalline carbonate phase in the early stages of the reaction does not significantly hinder brucite dissolution, as the carbonate coating remains sufficiently permeable. It is postulated that the conversion of this phase to substantially less porous, crystalline nesquehonite [MgCO3·3H2O] results in passivation of the brucite surface. Although a mechanistic model describing the passivating effect of nesquehonite remains elusive, reactive transport modeling using MIN3P-DUSTY confirms that conventional geometric surface area update models do not adequately reproduce observed reaction progress during brucite carbonation, while an empirically based model accounting for surface passivation is able to capture the transient evolution of CO2 uptake. Both water limits and surface passivation effects may limit the efficiency of CO2 sequestration efforts that rely on the conversion of mafic and ultramafic rock to carbonate minerals.

  17. Colloid Transport in Unsaturated Porous Media: The Role of Water Content and Ionic Strength on Particle Straining

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Packed column and mathematical modeling studies were conducted to explore the influence of water saturation, pore-water ionic strength, and grain size on the transport of latex microsphere colloids (1.1 micron) in porous media. Experiments were carried out under unfavorable conditions in terms of c...

  18. Users` manual for LEHGC: A Lagrangian-Eulerian Finite-Element Model of Hydrogeochemical Transport Through Saturated-Unsaturated Media. Version 1.1

    SciTech Connect

    Yeh, Gour-Tsyh; Carpenter, S.L.; Hopkins, P.L.; Siegel, M.D.

    1995-11-01

    The computer program LEHGC is a Hybrid Lagrangian-Eulerian Finite-Element Model of HydroGeo-Chemical (LEHGC) Transport Through Saturated-Unsaturated Media. LEHGC iteratively solves two-dimensional transport and geochemical equilibrium equations and is a descendant of HYDROGEOCHEM, a strictly Eulerian finite-element reactive transport code. The hybrid Lagrangian-Eulerian scheme improves on the Eulerian scheme by allowing larger time steps to be used in the advection-dominant transport calculations. This causes less numerical dispersion and alleviates the problem of calculated negative concentrations at sharp concentration fronts. The code also is more computationally efficient than the strictly Eulerian version. LEHGC is designed for generic application to reactive transport problems associated with contaminant transport in subsurface media. Input to the program includes the geometry of the system, the spatial distribution of finite elements and nodes, the properties of the media, the potential chemical reactions, and the initial and boundary conditions. Output includes the spatial distribution of chemical element concentrations as a function of time and space and the chemical speciation at user-specified nodes. LEHGC Version 1.1 is a modification of LEHGC Version 1.0. The modification includes: (1) devising a tracking algorithm with the computational effort proportional to N where N is the number of computational grid nodes rather than N{sup 2} as in LEHGC Version 1.0, (2) including multiple adsorbing sites and multiple ion-exchange sites, (3) using four preconditioned conjugate gradient methods for the solution of matrix equations, and (4) providing a model for some features of solute transport by colloids.

  19. Potential of pore water stable isotope for optimization of soil physical parameters and predicting flow and transport in the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Sprenger, M.; Weiler, M.

    2013-12-01

    by minimizing the sum of square residuals of observed and simulated data using the shuffled complex evolution algorithm. The Mualem-van Genuchten (MVG) parameters were optimized for all three inverse model approaches assuming two soil layers. For the two approaches, which included the isotope concentrations, also the longitudinal dispersivity parameter of the isotope transport had to be optimized. Hence, the inverse model approaches that considered natural tracers allowed for simulating and optimizing the intensity of mixing processes that occur in the vadose zone. The results show that the sole information of the pore water isotope content cannot substitute hydrometric information to derive MVG parameters. Though, adding data of natural tracers to soil moisture data helps understanding mixing and transport processes in the unsaturated zone. Model results emphasize the time variant composition of soil water ages across the soil depth over the year, which would not be possible in a sole hydrometric model approach. Therefore, stable isotope pore water profiles seem to be a promising tool to better understand processes taking place in the unsaturated zone and to compare sites with different soil properties and vegetation.

  20. [Effect of soil texture in unsaturated zone on soil nitrate accumulation and groundwater nitrate contamination in a marginal oasis in the middle of Heihe River basin].

    PubMed

    Su, Yong-Zhong; Yang, Xiao; Yang, Rong

    2014-10-01

    In irrigated agricultural ecosystems, the accumulation, distribution and transfer of nitrate nitrogen (NO(3-)-N) in soil profile and groundwater nitrate pollution were influenced by irrigation and fertilization, and were closely related to soil textural characteristics. In this study, a monitoring section with 10 groundwater observation wells along Heihe River flood land-old oasis croplands-newly cultivated sandy croplands-fixed sandy land outside oasis was established in Pingchuan desert-oasis in Linze county in the middle of Heihe river basin, and groundwater NO(3-)-N concentration was continuously monitored. Soil texture and NO(3-)-N concentration in the unsaturated zone at different landscape locations were determined. The NO(3-)-N transfer change in soil profile, nitrate leaching of soils with different texture and fertility levels in the 0-100 cm layer were analyzed. The results indicated that the vertical distribution of soil texture was sandy loam in the 0-130 cm depth, loam in the 130-190 cm and clay loam in the 190-300 cm for the old oasis croplands. For newly cultivated sandy croplands, sand content was more than 80% in each soil layer of the 0-300 cm profile, although a thin clay layer occurred in the 140-160 cm depth. The clay layer occurred 160 cm below the sand-fixing zone outside oasis. There were significant correlations between soil NO(3-)-N concentration and silt + clay content, and the order of significant degree was the natural soils of sandy lands > the newly cultivated sandy croplands > the old oasis croplands. The loss of N leaching was closely correlated to the silt + caly content in the 0-100 cm soil depth. The groundwater NO(3-)-N concentration varied from 1.01 to 5.17 mg · L(-1), with a mean value of 2.65 mg · L(-1) and from 6.6 to 29.5 mg · L(-1), with an average of 20.8 mg · L(-1) in the area of old oasis croplands and the newly cultivated croplands, respectively. The averaged groundwater NO(3-)-N concentration in the area of newly

  1. Water and tritium movement through the unsaturated zone at a low-level radioactive-waste disposal site near Sheffield, Illinois, 1981-85

    USGS Publications Warehouse

    Mills, Patrick C.; Healy, R.W.

    1991-01-01

    The movement of water and tritium through the unsaturated zone was studied at a low-level radioactive-waste disposal site near Sheffield, Bureau County, Illinois, from 1981 to 1985. Water and tritium movement occurred in an annual, seasonally timed cycle; recharge to the saturated zone generally occurred in the spring and early summer. Mean annual precipitation (1982-85) was 871 millimeters; mean annual recharge to the disposal trenches (July 1982 through June 1984) was estimated to be 107 millimeters. Average annual tritium flux below the study trenches was estimated to be 3.4 millicuries per year. Site geology, climate, and waste-disposal practices influenced the spatial and temporal variability of water and tritium movement. Of the components of the water budget, evapotranspiration contributed most to the temporal variability of water and tritium movement. Disposal trenches are constructed in complexly layered glacial and postglacial deposits that average 17 meters in thickness and overlie a thick sequence of Pennsylvanian shale. The horizontal saturated hydraulic conductivity of the clayey-silt to sand-sized glacial and postglacial deposits ranges from 4.8x10^-1 to 3.4x10^4 millimeters per day. A 120-meter-long horizontal tunnel provided access for hydrologic measurements and collection of sediment and water samples from the unsaturated and saturated geologic deposits below four disposal trenches. Trench-cover and subtrench deposits were monitored with soil-moisture tensiometers, vacuum and gravity lysimeters, piezometers, and a nuclear soil-moisture gage. A cross-sectional, numerical ground-water-flow model was used to simulate water movement in the variably saturated geologic deposits in the tunnel area. Concurrent studies at the site provided water-budget data for estimating recharge to the disposal trenches. Vertical water movement directly above the trenches was impeded by a zone of compaction within the clayey-silt trench covers. Water entered the

  2. Water and tritium movement through the unsaturated zone at a low-level radioactive-waste disposal site near Sheffield, Illinois, 1981-85

    USGS Publications Warehouse

    Mills, Patrick C.; Healy, Richard W.

    1993-01-01

    The movement of water and tritium through the unsaturated zone was studied at a low-level radioactive-waste disposal site near Sheffield, Bureau County, Illinois, from 1981 to 1985. Water and tritium movement occurred in an annual, seasonally timed cycle; recharge to the saturated zone generally occurred in the spring and early summer. Mean annual precipitation (1982-85) was 871 mm (millimeters); mean annual recharge to the disposal trenches (July 1982 through June 1984) was estimated to be 107 mm. Average annual tritium flux below the study trenches was estimated to be 3.4 mCi/yr (millicuries per year). Site geology, climate, and waste-disposal practices influenced the spatial and temporal variability of water and tritium movement. Of the components of the water budget, evapotranspiration contributed most to the temporal variability of water and tritium movement. Disposal trenches are constructed in complexly layered glacial and postglacial deposits that average 17 m (meters) in thickness and overlie a thick sequence of Pennsylvanian shale. The horizontal saturated hydraulic conductivity of the clayey-silt to sand-sized glacial and postglacial deposits ranges from 4.8x10 -1 to 3.4x10 4 mm/d (millimeters per day). A 120-m-long horizontal tunnel provided access for hydrologic measurements and collection of sediment and water samples from the unsaturated and saturated geologic deposits below four disposal trenches. Trench-cover and subtrench deposits were monitored with soil-moisture tensiometers, vacuum and gravity lysimeters, piezometers, and a nuclear soil-moisture gage. A cross-sectional, numerical ground-water-flow model was used to simulate water movement in the variably saturated geologic deposits in the tunnel area. Concurrent studies at the site provided water-budget data for estimating recharge to the disposal trenches. Vertical water movement directly above the trenches was impeded by a zone of compaction within the clayey-silt trench covers. Water entered

  3. A numerical model for the movement of H 2O, H 218O, and 2HHO in the unsaturated zone

    NASA Astrophysics Data System (ADS)

    Shurbaji, Abdel-Rahman M.; Phillips, Fred M.

    1995-09-01

    Vertical profiles of H 218O and 2HHO concentrations have yielded useful information on evaporation and infiltration processes in soils. However, in the field, quantitative interpretation of such profiles has been limited by the restrictions inherent in the quasi-steady-state and transient analytical models available to describe the physical processes. This study presents a flexible numerical model that simulates transient fluxes of heat, liquid water, water vapor, and isotopic species. The model can simulate both infiltration and evaporation under fluctuating meteorological conditions and thus should be useful in reproducing changes in field isotope profiles. A transition factor is introduced in the isotope transport equation. This factor combines hydrologic and isotopic parameters and changes slowly with depth in the soil profile but strongly in the evaporation zone, owing to the rapid change in the dominant phase of water from liquid to vapor. Using the transition factor in the isotope transport equation facilitates obtaining the typical shape of the isotope profile (bulge at the evaporation zone). This factor also facilitates producing broad isotope enrichment peaks that may be seen in very dry soils.

  4. Hydrological, meteorological and geohydrological data for an unsaturated zone study near the Radioactive Waste Management Complex, Idaho National Engineering Laboratory, Idaho - 1987

    SciTech Connect

    Davis, L.C.; Pittman, J.R. )

    1990-01-01

    Since 1952, radioactive waste has been buried at the RWMC (Radioactive Waste Management Complex) at the Idaho National Engineering Laboratory in southeastern Idaho. In 1985, the US Geological Survey, in cooperation with the US Department of Energy, began a study of the geohydrology of the RWMC to provide a basis for estimating the extent of and the potential for migration of radionuclides in the unsaturated zone beneath the waste burial trenches and pits. This study is being conducted to provide hydrological, meteorological and geohydrological data for the test trench area adjacent to the northern boundary of the RWMC. During 1987, data were collected from the test trench area, where several types of instrumentation were installed in the surficial sediment in 1985. Hydrological data collected from both disturbed and undisturbed soil included measurements, from 28 thermocouple psychrometers placed at selected depths to about 6m. Soil moisture content measurements were collected bi-weekly in 9 neutron-probe access holes with a neutron moisture depth gage. Meteorological data summarized daily included: (1) incoming and emitted long-wave radiation; (2) incoming and reflected short-wave radiation; (3) air temperature; (4) relative humidity; (5) wind speed; (6) wind direction; and (7) precipitation. To describe grain-size distribution with depth, 17 samples were analyzed using sieve and pipette methods. Statistical parameters, carbonate content, color, particle roundness and sphericity, and mineralogic and clastic constituents were determined for each sample. Some samples were analyzed by x-ray diffraction techniques to determine bulk and clay mineralogy.

  5. Comparison of the stable-isotopic composition of soil water collected from suction lysimeters, wick samplers, and cores in a sandy unsaturated zone

    USGS Publications Warehouse

    Landon, M.K.; Delin, G.N.; Komor, S.C.; Regan, C.P.

    1999-01-01

    Soil water collected from suction lysimeters and wick samplers buried in the unsaturated zone of a sand and gravel aquifer and extracted from soil cores were analyzed for stable oxygen and hydrogen isotope values. Soil water isotopic values differed among the three sampling methods in most cases. However, because each sampling method collected different fractions of the total soil-water reservoir, the isotopic differences indicated that the soil water at a given depth and time was isotopically heterogeneous. This heterogeneity reflects the presence of relatively more and less mobile components of soil water. Isotopic results from three field tests indicated that 95–100% of the water collected from wick samplers was mobile soil water while samples from suction lysimeters and cores were mixtures of more and less mobile soil water. Suction lysimeter samples contained a higher proportion of more mobile water (15–95%) than samples from cores (5–80%) at the same depth. The results of this study indicate that, during infiltration events, soil water collected with wick samplers is more representative of the mobile soil water that is likely to recharge ground water during or soon after the event than soil water from suction lysimeters or cores.

  6. Chemistry of unsaturated zone gases sampled in open boreholes at the crest of Yucca Mountain, Nevada: Data and basic concepts of chemical and physical processes in the mountain

    NASA Astrophysics Data System (ADS)

    Thorstenson, Donald C.; Weeks, Edwin P.; Haas, Herbert; Busenberg, Eurybiades; Plummer, L. Niel; Peters, Charles A.

    Boreholes open to the unsaturated zone at the crest of Yucca Mountain, Nevada, were variously sampled for CO2 (including 13C and 14C), CH4, N2, O2, Ar, CFC-11, CFC-12, and CFC-113 from 1986 to 1993. Air enters the mountain in outcrops, principally on the eastern slope, is enriched in CO2 by mixing with soil gas, and is advected to the mountain crest, where it returns to the atmosphere. The CFC data indicate that travel times of the advecting gas in the shallow Tiva Canyon hydrogeologic unit are <=5 years. The 14C activities are postbomb to depths of 100 m, indicating little retardation of 14CO2 in the shallow flow systems. The 14C activities from 168 to 404 m in the Topopah Spring hydrogeologic unit are 85-90 pMC at borehole USW-UZ6. The CFC data show that the drilling of USW-UZ6 in 1984 has altered the natural system by providing a conduit through the Paintbrush Nonwelded unit, allowing flow from Topopah Spring outcrops in Solitario Canyon on the west to USW-UZ6, upward in the borehole through the Paintbrush, to the shallow Tiva Canyon flow systems, and out of the mountain.

  7. Concepts and data-collection techniques used in a study of the unsaturated zone at a low-level radioactive-waste disposal site near Sheffield, Illinois

    USGS Publications Warehouse

    Healy, R.W.; DeVries, M.P.; Striegl, R.G.

    1986-01-01

    A study of water and radionuclide movement through the unsaturated zone is being conducted at the low level radioactive waste disposal site near Sheffield, Illinois. Included in the study are detailed investigations of evapotranspiration, movement of water through waste trench covers, and movement of water and radionuclides (dissolved and gaseous) from the trenches. An energy balance/Bowen ratio approach is used to determine evapotranspiration. Precipitation, net radiation, soil-heat flux, air temperature and water vapor content gradients, wind speed, and wind direction are measured. Soil water tension is measured with tensiometers which are connected to pressure transducers. Meteorological sensors and tensiometers which are connected to pressure transducers. Meteorological sensors and tensiometers are monitored with automatic data loggers. Soil moisture contents are measured through small-diameter access tubes with neutron and gamma-ray attenuation gages. Data beneath the trenches are obtained through a 130-meter-long tunnel which extends under four of the trenches. Water samples are obtained with suction lysimeters, and samples of the geologic material are obtained with core tubes. These samples are analyzed for radiometric and inorganic chemistry. Gas samples are obtained from gas piezometers and analyzed for partial pressures of major constituents, Radon-222, tritiated water vapor, and carbon-14 dioxide. (USGS)

  8. Chemistry of unsaturated zone gases sampled in open boreholes at the crest of Yucca Mountain, Nevada: Data and basic concepts of chemical and physical processes in the mountain

    USGS Publications Warehouse

    Thorstenson, D.C.; Weeks, E.P.; Haas, H.; Busenberg, E.; Plummer, L.N.; Peters, C.A.

    1998-01-01

    Boreholes open to the unsaturated zone at the crest of Yucca Mountain, Nevada, were variously sampled for CO2 (including 13C and 14C), CH4, N2, O2, Ar, CFC-11, CFC12, and CFC-113 from 1986 to 1993. Air enters the mountain in outcrops, principally on the eastern slope, is enriched in CO2 by mixing with soil gas, and is advected to the mountain crest, where it returns to the atmosphere. The CFC data indicate that travel times of the advecting gas in the shallow Tiva Canyon hydrogeologic unit are ???5 years. The 14C activities are postbomb to depths of 100 m, indicating little retardation of 14CO2 in the shallow flow systems. The 14C activities from 168 to 404 m in the Topopah Spring hydrogeologic unit are 85-90 pMC at borehole USW-UZ6. The CFC data show that the drilling of USW-UZ6 in 1984 has altered the natural system by providing a conduit through the Paintbrush Nonwelded unit, allowing flow from Topopah Spring outcrops in Solitario Canyon on the west to USW-UZ6, upward in the borehole through the Paintbrush, to the shallow Tiva Canyon flow systems, and out of the mountain.

  9. Abstracts and parameter index database for reports pertaining to the unsaturated zone and surface water-ground water interactions at the Idaho National Engineering Laboratory

    SciTech Connect

    Bloomsburg, G.; Finnie, J.; Horn, D.; King, B.; Liou, J.

    1993-05-01

    This report is a product generated by faculty at the University of Idaho in support of research and development projects on Unsaturated Zone Contamination and Transport Processes, and on Surface Water-Groundwater Interactions and Regional Groundwater Flow at the Idaho National Engineering Laboratory. These projects are managed by the State of Idaho`s INEL Oversight Program under a grant from the US Department of Energy. In particular, this report meets project objectives to produce a site-wide summary of hydrological information based on a literature search and review of field, laboratory and modeling studies at INEL, including a cross-referenced index to site-specific physical, chemical, mineralogic, geologic and hydrologic parameters determined from these studies. This report includes abstracts of 149 reports with hydrological information. For reports which focus on hydrological issues, the abstracts are taken directly from those reports; for reports dealing with a variety of issues beside hydrology, the abstracts were generated by the University of Idaho authors concentrating on hydrology-related issues. Each abstract is followed by a ``Data`` section which identifies types of technical information included in a given report, such as information on parameters or chemistry, mineralogy, stream flows, water levels. The ``Data`` section does not include actual values or data.

  10. Impact of material heterogeneity on solute transport behavior in the unsaturated zone of the Calcaire de Beauce aquifer (France)

    NASA Astrophysics Data System (ADS)

    Viel, Emelie; Coquet, Yves

    2016-04-01

    Since a few decades, the Calcaire de Beauce aquifer is contaminated with nitrate. The nitrate dynamics in the aquifer and in the surface soil are quite well understood, but its transport through the vadose zone remains largely unknown. When models fail to simulate nitrate concentrations in wells, preferential flow or physical non-equilibrium transport in soil and in the vadose zone is usually put forward to explain this failure. To study transport processes in the vadose zone of the Calcaire de Beauce aquifer, undisturbed cores (30 cm length and 20 cm diameter) have been taken below the deepest soil horizon. At the field scale, the vadose zone is composed of powdery limestone spatially very heterogeneous, and including a variable amount of coarse elements. Two columns were selected: column "6" is made of very fine homogeneous limestone whereas column "8" is very heterogeneous with a large proportion of coarse elements. Elution experiments have been performed on both columns. A tracer (Br- or DFBA) in a solution of 5 mM CaCl2 was spread as a pulse on the top of the column with a rainfall simulator. Input flow rate was kept constant for steady state cases, or suddenly closed for flux interruption cases. Outflow was collected as a function of time for tracer concentration measurement. The collected fractions were analyzed by HPLC (High-performance liquid chromatography) with a UV detector. Three types of experiments took place: • For steady state experiments, three rainfall rates, respectively 4, 8, and 16 mm/h, have been used to study the occurrence of immobile water in the columns. The tracer was injected during 120 min followed by CaCl2 tracer-free solution at same flow rate. • For flux-interruption experiments, only the 4 and 8 mm/h rainfall rates were used. The tracer was injected during 120 min, input and output fluxes were then stopped and restarted seven days later with the same flow rate. • For drainage experiments, only the 4 and 8 mm/h rainfall rates

  11. Determining the stable isotope composition of pore water from saturated and unsaturated zone core: improvements to the direct vapour equilibration laser spectrometry method

    NASA Astrophysics Data System (ADS)

    Hendry, M. J.; Schmeling, E.; Wassenaar, L. I.; Barbour, S. L.; Pratt, D.

    2015-11-01

    A method to measure the δ2H and δ18O composition of pore waters in saturated and unsaturated geologic core samples using direct vapour equilibration and laser spectrometry (DVE-LS) was first described in 2008, and has since been rapidly adopted. Here, we describe a number of important methodological improvements and limitations encountered in routine application of DVE-LS over several years. Generally, good comparative agreement, as well as accuracy, is obtained between core pore water isotopic data obtained using DVE-LS and that measured on water squeezed from the same core. In complex hydrogeologic settings, high-resolution DVE-LS depth profiles provide greater spatial resolution of isotopic profiles compared to long-screened or nested piezometers. When fluid is used during drilling and coring (e.g. water rotary or wet sonic drill methods), spiking the drill fluid with 2H can be conducted to identify core contamination. DVE-LS analyses yield accurate formational isotopic data for fine-textured core (e.g. clay, shale) samples, but are less effective for cores obtained from saturated permeable (e.g. sand, gravels) geologic media or on chip samples that are easily contaminated by wet rotary drilling fluid. Data obtained from DVE-LS analyses of core samples collected using wet (contamination by drill water) and dry sonic (water loss by heating) methods were also problematic. Accurate DVE-LS results can be obtained on core samples with gravimetric water contents > 5 % by increasing the sample size tested. Inexpensive Ziploc™ gas-sampling bags were determined to be as good as, if not better than, other, more expensive specialty bags. Sample storage in sample bags provides acceptable results for up to 10 days of storage; however, measurable water loss, as well as evaporitic isotopic enrichment, occurs for samples stored for up to 6 months. With appropriate care taken during sample collection and storage, the DVE-LS approach for obtaining high-resolution pore water

  12. Determining the stable isotope composition of pore water from saturated and unsaturated zone core: improvements to the direct vapor equilibration laser spectroscopy method

    NASA Astrophysics Data System (ADS)

    Hendry, M. J.; Schmeling, E.; Wassenaar, L. I.; Barbour, S. L.; Pratt, D.

    2015-06-01

    A method to measure the δ2H and δ18O composition of pore waters in saturated and unsaturated geologic core samples using direct vapor equilibration and laser spectroscopy (DVE-LS) was first described in 2008, and has since been widely adopted by others. Here, we describe a number of important methodological improvements and limitations encountered in routine application of DVE-LS over several years. Generally, good comparative agreement and accuracy is obtained between core pore water isotopic data obtained using DVE-LS and that measured on water squeezed from the same core. In complex hydrogeologic settings, high-resolution DVE-LS depth profiles provide greater spatial resolution of isotopic profiles compared to long-screened or nested piezometers. When fluid is used during drilling and coring (e.g., water rotary or wet sonic drill methods), spiking the drill fluid with 2H can be conducted to identify core contamination. DVE-LS analyses yield accurate formational isotopic data for fine-textured core (e.g., clay, shale) samples, but are less effective for cores obtained from saturated permeable (e.g., sand, gravels) geologic media or on chip samples that are easily contaminated by wet rotary drilling fluid. Data obtained from DVE-LS analyses of core samples collected using wet (contamination by drill water) and dry sonic (water loss by heating) methods were also problematic. Accurate DVE-LS results can be obtained on core samples with gravimetric water contents < 5 % by increasing the sample size tested. Inexpensive Ziploc™ gas sampling bags were determined to be as good as, if not better, than other, more expensive bags. Sample storage in gas tight sample bags provides acceptable results for up to 10 days of storage; however, measureable water loss and evaporitic isotopic enrichment occurs for samples stored for up to 6 months. With appropriate care taken during sample collection and storage, the DVE-LS approach for obtaining high resolution pore water

  13. Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study

    NASA Astrophysics Data System (ADS)

    Molins, S.; Mayer, K. U.

    2007-05-01

    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.

  14. Determination of nitroaromatic explosives and their degradation products in unsaturated-zone water samples by high-performance liquid chromatography with photodiode-array, mass spectrometric, and tandem mass spectrometric detection

    USGS Publications Warehouse

    Gates, Paul M.; Furlong, E.T.; Dorsey, T.F.; Burkhardt, M.R.

    1996-01-01

    Mass spectrometry and tandem mass spectrometry, coupled by a thermospray interface to a high-performance liguid chromatography system and equipped with a photodiode array detector, were used to determine the presence of nitroaromatic explosives and their degradation products in USA unsaturated-zone water samples. Using this approach, the lower limits of quantitation for explosives determined by mass spectrometry in this study typically ranged from 10 to 100 ng/l.

  15. Occurrence and spatial distribution of emerging contaminants in the unsaturated zone. case study: Guadalete River basin (Cadiz, Spain).

    PubMed

    Corada-Fernández, Carmen; Jiménez-Martínez, Joaquín; Candela, Lucila; González-Mazo, Eduardo; Lara-Martín, Pablo A

    2015-01-01

    Irrigation with reclaimed water is becoming a common practice in arid- and semi-arid regions as a consequence of structural water resource scarcity. This practice can lead to contamination of the vadose zone if sewage-derived contaminants are not removed properly. In the current work, we have characterized soils from the Guadalete River basin (SW Spain), which are often irrigated with reclaimed water from a nearby wastewater treatment plant and amended using sludge. Physico-chemical, mineralogical and hydraulic properties were measured in soil samples from this area (from surface up to 2 m depth). Emerging contaminants (synthetic surfactants and pharmaceutically active compounds, or PhACs) were also determined. Synthetic surfactants, widely used in personal care products (PCPs), were found in a wide range of concentrations: 73-1300 μg kg(-1) for linear alkylbenzene sulfonates (LAS), 120-496 μg kg(-1) for alkyl ethoxysulfates (AES), 19-1090 μg kg(-1) for alcohol polyethoxylates (AEOs), and 155-280 μg kg(-1) for nonylphenol polyethoxylates (NPEOs). The presence of surfactant homologues with longer alkyl chains was predominant due to their sorption capacity. A positive correlation was found between LAS and AEOs and soil organic carbon and clay content, respectively. Out of 64 PhACs analyzed, only 7 were detected occasionally (diclofenac, metoprolol, fenofibrate, carbamazepine, clarithromycin, famotidine and hydrochlorothiazide), always at very low concentrations (from 0.1 to 1.3 μg kg(-1)). PMID:24890839

  16. Representative elementary volume estimation for porosity, moisture saturation, and air-water interfacial areas in unsaturated porous media: Data quality implications

    SciTech Connect

    Costanza-Robinson, Molly S.; Estabrook, Benjamin D.; Fouhey, David F.

    2011-09-16

    Achieving a representative elementary volume (REV) has become a de facto criterion for demonstrating the quality of {mu}CT measurements in porous media systems. However, the data quality implications of an REV requirement have not been previously examined. In this work, deterministic REVs for porosity, moisture saturation (S{sub W}), and air-water interfacial area (A{sub I}) were estimated using a set of 49 {mu}CT images of eight unsaturated homogeneous porous media with heterogeneity in moisture distributions present in varying degrees. Estimated porosity REVs were <8 mm{sup 3} for all cases, smaller than typical CT image sizes ({approx}100 mm{sup 3}). Estimated S{sub W} and A{sub I} REVs were <55 mm{sup 3} for cases with homogeneous moisture distributions but could not be estimated for cases with heterogeneous moisture distributions, due to the absence of a distinct 'REV plateau' within the maximum imaged volume. Conventionally, S{sub W} and A{sub I} data from such non-REV cases would be excluded. The implications of excluding data on the basis of REV were examined by comparing A{sub I}-S{sub W} data measured on image windows of increasing size against the expected linear A{sub I}-S{sub W} relationship. At measurement scales exceeding porosity REV, random fluctuations in A{sub I}-S{sub W} data were excluded, even for cases containing heterogeneous moisture distributions. In contrast, requiring measurement scales to exceed S{sub W} and A{sub I} REV appeared overly restrictive and resulted in visible loss of reliable A{sub I}-S{sub W} data. We attribute these findings to overestimation of REVs due to inherently problematic estimation of deterministic REVs in real systems. Implications of these findings for ensuring CT data quality and the efficient use of CT data are discussed.

  17. Long-term transfer of diffuse pollution at catchment scale: Respective roles of soil, and the unsaturated and saturated zones (Brévilles, France)

    NASA Astrophysics Data System (ADS)

    Gutierrez, A.; Baran, N.

    2009-05-01

    SummaryEnvironmental management such as recommended by the European Water Framework Directive requires actions regarding diffuse pollution. However, the efficiency of these actions depends on the reaction time of the hydrosystem. In order to predict future groundwater-quality trends, especially after implementation of environmental measures such as substitution of pesticides or reduction of nitrogen loads, the response time has to be determined. In the case of diffuse pollution, the response time between fertilizer or pesticide application and the subsequent contamination of a spring or well may depend on the distance between the area where the products are spread and the point where water quality is measured. However, some aquifer systems may appear particularly slow, independently of the size of the catchment. At Montreuil-sur-Epte (Val d'Oise, France), no significant change in groundwater quality can be related to the suppression of atrazine application over the small agricultural catchment (4 sq km) of the Brévilles spring, 8 years ago (4 years before the national ban of atrazine). Besides the 8 year monitoring of groundwater quality at the spring and in several observation wells in its catchment, a particular attention was paid to the characterization of water and solute-infiltration rates at different scales. The role of each compartment (soil, and unsaturated and saturated zones) in the slowing down of flow and the transfer of solutes (pesticides and nitrate) from top soil to aquifer, and then to the spring, was determined by a multidisciplinary approach involving mainly soil science, hydrogeology and geochemistry. Detailed investigations aimed at identifying and quantifying the parameters that contribute to the inertia of the system, resulting in a long-term transfer of diffuse pollution. Data covering the monitoring of pesticide transfer in soil, the physico-chemical characteristics of soils, profiles of water contents, tritium activities, and nitrate

  18. The impact of immobile zones on the transport and retention of nanoparticles in porous media

    NASA Astrophysics Data System (ADS)

    Molnar, Ian L.; Gerhard, Jason I.; Willson, Clinton S.; O'Carroll, Denis M.

    2015-11-01

    Nanoparticle transport and retention within porous media is treated by conceptualizing the porous media as a series of independent collectors (e.g., Colloid Filtration Theory). This conceptualization assumes that flow phenomena near grain-grain contacts, such as immobile zones (areas of low flow), exert a negligible influence on nanoparticle transport and assumes that retention and release of particles depends only on surface chemistry. This study investigated the impact of immobile zones on nanoparticle transport and retention by employing synchrotron X-ray computed microtomography (SXCMT) to examine pore-scale silver nanoparticle distributions during transport through three sand columns: uniform iron oxide, uniform quartz, and well-graded quartz. Extended tailing was observed during the elution phase of all experiments suggesting that hydraulic retention in immobile zones, not detachment from grains, was the source of tailing. A numerical simulation of fluid flow through an SXCMT data set predicted the presence of immobile zones near grain-grain contacts. SXCMT-determined silver nanoparticle concentrations observed that significantly lower nanoparticle concentrations existed near grain-grain contacts throughout the duration of all experiments. In addition, the SXCMT-determined pore-scale concentration gradients were found to be independent of surface chemistry and grain size distribution, suggesting that immobile zones limit the diffusive transport of nanoparticles toward the collectors. These results suggest that the well-known overprediction of nanoparticle retention by traditional CFT may be due to ignoring the influences of grain-grain contacts and immobile zones. As such, accurate prediction of nanoparticle transport requires consideration of immobile zones and their influence on both hydraulic and surface retention.

  19. Computation of the transient flow in zoned anisotropic porous media by the boundary element method

    NASA Astrophysics Data System (ADS)

    Bruch, E.; Grilli, S.

    Results on the application of the BEM to transient two-dimensional flows in zoned anisotropic porous media are presented, including the iterative calculation of the free surface seepage position. The classical BEM equations are discretized by linear, quadratic, or cubic elements, employing special singular numerical quadrature rules. The method is improved by the incorporation of a subregion division. The present technique is shown to be very accurate and to avoid previously encountered oscillation problems.

  20. Steady convective flow in an unsaturated state dependent anisotropic soil profile: Analysis of the affected zone from a contaminating point source

    NASA Astrophysics Data System (ADS)

    Cohen, M.; Mualem, Y.

    2011-01-01

    SummaryAnisotropy of the medium plays a dominant role in shaping the flow pattern in the soil profile. This study analyses the effect of anisotropy on the horizontal spreading of the flow trajectories from a contaminating source point at the soil surface to a high water table. It considers a phreatic aquifer with infinite lateral extension and uniform sedimentary-layered soil profile, where a state dependent anisotropy factor (SDAF) - A( ψ), and Mualem's (1984) anisotropy model might be applicable. The numerically calculated streamlines portray the effect of anisotropy, and allow discernment among various anisotropic media. Different flow cases are analyzed with regard to their dependence on A( ψ), as well as their dependence on the infiltration rate, and on the orientation of the principal axes. Theory indicates that the flux direction is dependent on the capillary head and thus on the flow rate. Consequently, it is the infiltration rate, which determines the particular path line from the contaminant source point to the ground water table. Accordingly, we have defined the "affected domain" as the domain within the unsaturated profile which is vulnerable to contamination from a source point at the soil surface, and the "affected segment" as the segment on the phreatic surface where pollutants may potentially reach the ground water aquifer. Both are determined with respect to anisotropy, infiltration rate, and depth. The non-linear horizontal shift of the contaminant trajectory indicates that a substantial error may result when adopting a constant anisotropy factor. This study suggests that the maximal horizontal shift is the relevant scale when characterizing the anisotropic flow system. This measure should be taken into consideration when designing a related laboratory experiment or a field monitoring system.

  1. 3DFEMWATER: A three-dimensional finite element model of water flow through saturated-unsaturated media

    SciTech Connect

    Yeh, G.T.

    1987-08-01

    The 3DFEMWATER model is designed to treat heterogeneous and anisotropic media consisting of as many geologic formations as desired, consider both distributed and point sources/sinks that are spatially and temporally dependent, accept the prescribed initial conditions or obtain them by simulating a steady state version of the system under consideration, deal with a transient head distributed over the Dirichlet boundary, handle time-dependent fluxes due to pressure gradient varying along the Neumann boundary, treat time-dependent total fluxes distributed over the Cauchy boundary, automatically determine variable boundary conditions of evaporation, infiltration, or seepage on the soil-air interface, include the off-diagonal hydraulic conductivity components in the modified Richards equation for dealing with cases when the coordinate system does not coincide with the principal directions of the hydraulic conductivity tensor, give three options for estimating the nonlinear matrix, include two options (successive subregion block iterations and successive point interactions) for solving the linearized matrix equations, automatically reset time step size when boundary conditions or source/sinks change abruptly, and check the mass balance computation over the entire region for every time step. The model is verified with analytical solutions or other numerical models for three examples.

  2. A novel automated fluctuating water table column system to study redox oscillations in saturated and unsaturated media

    NASA Astrophysics Data System (ADS)

    Rezanezhad, F.; Couture, R.-M.; Kovac, R.; Van Cappellen, P.

    2012-04-01

    An automated, computer-controlled soil column experimental setup was developed to simulate in detail the effects of water table dynamics on the biogeochemical transformations of nutrients and other redox-sensitive chemical species at the interface between groundwater and surface waters. The experiments were conducted using two parallel soil columns, one under stable and the other under fluctuating water table conditions. The water table in the soil columns was controlled by an automated multi-channel pump connected to two equilibrium and storage columns. In the stable column, the water table was maintained at -20 cm below the soil surface while it fluctuated between the soil surface and -45 cm in the fluctuating column at a rate of 4.8 cm/d. Redox potential (Eh), pH profiles were measured continuously using high temporal resolution microsensors (10 μm glass tip) installed into the columns at different depths. The results show striking geochemical contrasts between the fluctuating and the stable columns, demonstrating that the setup is able to impose redox potential oscillations ranging from oxidizing (~+700 mv) to reducing (~-200 mv) conditions. CO2 fluxes were monitored in the headspace above the soil surface using a LICOR LI-8100 automated soil CO2 flux system. The mean CO2 emission in the stable water table column was ~20 ppm/min. In the fluctuating soil column, the CO2 flux varied between 4 and 110 ppm/min and the lowest were measured at the highest water level. Water samples obtained from micro-Rhizon samplers installed into the columns at various depths. Additionally, the physical, chemical and microbial characteristics of the media were characterized by centimetre scale slicing of the soil columns at the end of the experiment. The impacting of these oscillations on the distribution of chemical species will be discussed in term of the interactions between soils, solutes, microbial activity, and hydrology.

  3. Data from a Thick Unsaturated Zone Underlying Two Artificial Recharge Sites along Oro Grande Wash in the Western Part of the Mojave Desert, near Victorville, San Bernardino County, California, 2001-2006

    USGS Publications Warehouse

    Clark, Dennis A.; Izbicki, John A.; Johnson, Russell D.; Land, Michael

    2009-01-01

    This report presents data on the physical and hydraulic properties of unsaturated alluvial deposits and on the chemical and isotopic composition of water collected at two recharge sites in the western part of the Mojave Desert, near Victorville, California, from 2001 to 2006. Unsaturated-zone monitoring sites were installed adjacent to the two recharge ponds using the ODEX air-hammer and air rotary method to depths of about 460 feet and 269 feet below land surface. Each of the two unsaturated-zone monitoring sites included a water-table well, matric-potential sensors, and suction-cup lysimeters installed in a single bore hole. Drilling procedures, lithologic and geophysical data, and site construction and instrumentation are described. Core material was analyzed for water content, bulk density, water potential, particle size, and water retention. The chemical composition of leachate from almost 400 samples of cores and cuttings was determined. Water from suction-cup lysimeters also was analyzed for chemical and isotopic composition. In addition, data on the chemical and isotopic composition of groundwater from the two water-table wells are reported along with chemical and isotopic composition of the surface water in the recharge ponds.

  4. Treatment of chlorinated solvents by nitrogen-fixing and nitrate-supplied methane oxidizers in columns packed with unsaturated porous media

    SciTech Connect

    Chu, K.H.; Alvarez-Cohen, L.

    2000-05-01

    This study compares the feasibility of employing nitrogen-fixing and nitrate-supplied methane-oxidizing cultures grown in unsaturated porous media to degrade cis-1,2-dichloroethylene (cDCE) and trichloroethylene (TCE) in gas streams. Both nitrate-supplied and nitrogen-fixing columns degraded TCE completely at a gaseous concentration of 0.7 mg/L for 8--10 days. However, when columns were supplied with 4% CH{sub 4} and 10% O{sub 2}, nitrate-supplied columns were not able to recover after degrading TCE at a gaseous concentration of 0.13 mg/L for 7 days. In contrast, nitrogen-fixing columns recovered after degrading 0.13--0.4 mg/L TCE for 3--10 days and were capable of repeatedly degrading TCE at gaseous concentrations of 0.03--0.14 mg/L TCE for 3--10 days and were capable of repeatedly degrading TCE at gaseous concentrations of 0.03--0.14 mg/L during long-term intermittent operation that was punctuated by appropriate microbial recovery periods. Both nitrate-supplied and nitrogen-fixing columns were capable of degrading cDCE at concentrations of 0.7--1.0 mg/L for 5--10 days, but only the nitrogen-fixing columns recovered from cDCE exposure. The operating period for columns treating a mixture of TCE and cDCE was significantly shorter than that for treatment of TCE or cDCE alone. Several operating curves were developed to facilitate comparisons between operating conditions and to aid in predicting chlorinated solvent removals in such systems. Nitrogen-fixing columns consistently outperformed nitrate-supplied columns, and columns inoculated with a mixed culture outperformed those inoculated with Methylosinus trichosporium OB3b for TCE removal but not for cDCE removal.

  5. Non-invasive investigation of the saturated/unsaturated zone with magnetic resonance sounding - a field example at the testsite Fuhrberger Feld near Hannover, Germany

    NASA Astrophysics Data System (ADS)

    Costabel, S.; Noell, U.; Ganz, C.

    2012-04-01

    Magnetic resonance sounding (MRS) is a non-invasive geophysical method for groundwater prospection that uses the principle of nuclear magnetic resonance (NMR) in the Earth's magnetic field. Its unique property distinct from other hydrogeophysical methods is the direct sensitivity to the amount of water, i.e. to the amount of 1H nuclei in the subsurface. Because MRS is normally used to investigate the water content of the saturated zone and to characterize aquifer structures, the standard application is optimized for 1D-measurements in depths from several to several tens of meters. However, our investigations show that MRS has also the potential to contribute substantially to the study of groundwater recharge if the sensitivity of the method for the unsaturated zone and for the transition to the saturated zone is increased by using a modified measurement setup and adjusted interpretation schemes. We conducted MRS test measurements with the focus on the very shallow subsurface in the range of some few decimeters down to the groundwater table in a depth of 3 m. The test site is located in the area Fuhrberger Feld about 30 km north-east of Hannover, Germany, which comprises an unconfined sandy aquifer of 20 to 30-m thickness. Previous studies have discovered the soil physical characteristics of the site with tension infiltrometer measurements and tracer irrigation experiments in the field, as well as with water retention measurements in the laboratory. In addition, several infiltration experiments with dye tracer were conducted and monitored with electrical resistivity tomography (ERT), tensiometers and TDR devices. For the MRS measurements at the testsite, a serious challenge was the intense electromagnetic noise consisting of large spiky radio signals and harmonic components, respectively. A special combination of new processing techniques was developed to isolate and interpret the NMR signals with amplitudes of approximately 5 to 14 nV. The standard inversion of the

  6. Determination of degradation rates of organic substances in the unsaturated soil zone depending on the grain size fractions of various soil types

    NASA Astrophysics Data System (ADS)

    Fichtner, Thomas; Stefan, Catalin; Goersmeyer, Nora

    2015-04-01

    Rate and extent of the biological degradation of organic substances during transport through the unsaturated soil zone is decisively influenced by the chemical and physical properties of the pollutants such as water solubility, toxicity and molecular structure. Furthermore microbial degradation processes are also influenced by soil-specific properties. An important parameter is the soil grain size distribution on which the pore volume and the pore size depends. Changes lead to changes in air and water circulation as well as preferred flow paths. Transport capacity of water inclusive nutrients is lower in existing bad-drainable fine pores in soils with small grain size fractions than in well-drainable coarse pores in a soil with bigger grain size fractions. Because fine pores are saturated with water for a longer time than the coarse pores and oxygen diffusion in water is ten thousand times slower than in air, oxygen is replenished much slower in soils with small grain size fractions. As a result life and growth conditions of the microorganisms are negatively affected. This leads to less biological activity, restricted degradation/mineralization of pollutants or altered microbial processes. The aim of conducted laboratory column experiments was to study the correlation between the grain size fractions respectively pore sizes, the oxygen content and the biodegradation rate of infiltrated organic substances. Therefore two columns (active + sterile control) were filled with different grain size fractions (0,063-0,125 mm, 0,2-0,63 mm and 1-2 mm) of soils. The sterile soil was inoculated with a defined amount of a special bacteria culture (sphingobium yanoikuae). A solution with organic substances glucose, oxalic acid, sinaphylic alcohol and nutrients was infiltrated from the top in intervals. The degradation of organic substances was controlled by the measurement of dissolved organic carbon in the in- and outflow of the column. The control of different pore volumes

  7. Time-lapse resistivity measurements combined with soil water sampling to characterize solute movement in the unsaturated zone at Oslo airport, Gardermoen

    NASA Astrophysics Data System (ADS)

    Bloem, E.; French, H. K.; Binley, A.; Schotanus, D.; Eggen, G.

    2010-12-01

    Pollution of soils is a widespread problem and is an important part of the still to be implemented Soil Directive (EU). To improve risk assessment, monitoring, and treatment strategies for natural attenuation, we require a better understanding of the effect of soil heterogeneity on contaminant movement and methods for monitoring the effects of this heterogeneity at contaminated sites. Geophysical methods provide indirect measurements of subsurface properties over larger volumes than tradition techniques, and are potentially cost-efficient. However, the usefulness of any individual set of geophysical measurements (akin to a snapshot at one point in time) is severely limited by the problem of non-uniqueness or ambiguity when used to study contaminated sites, where the attendant processes vary in space and time. To make progress on soil contamination assessment and site characterization there is a strong need to integrate quasi field-scale, extensively instrumented tools, such as the multi-compartment sampler, with non-invasive (geophysical) and invasive (soil sampling, soil water sampling) methods. We illustrate this approach in an application to solute transport at Oslo airport, Norway. The impact of annual infiltration of large quantities of de-icing chemicals at Oslo airport, Gardermoen, represents common challenge for all airports with winter frost. It is also similar to the challenge posed by de-icing salt application along roads. At the research field station at Gardermoen, a degradable de-icing chemical and an inactive tracer were added to the snow cover prior to snowmelt and to the surface during an irrigation experiment performed after the snowmelt. In order to link geophysical measurements to solute transport processes in the unsaturated zone, time-lapse cross borehole resistivity as well as surface resistivity measurements were conducted at the same time as soil water samples were extracted. Measurements of soil temperature, and tension were also carried

  8. Relative Abundances of Calcite and Silica in Fracture Coatings as a Possible Indicator of Evaporation in a Thick Unsaturated Zone, Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Marshall, B. D.; Moscati, R. J.

    2005-12-01

    Yucca Mountain, a ridge of shallowly dipping, Miocene-age volcanic rocks in southwest Nevada, is the proposed site for a nuclear waste repository to be constructed in the 500- to 700-m-thick unsaturated zone (UZ). At the proposed repository, the 300-m-thick Topopah Spring Tuff welded unit (TSw) is overlain by approximately 30 m of nonwelded tuffs (PTn); the Tiva Canyon Tuff welded unit (TCw) overlies the PTn with a range in thickness from 0 to approximately 130 m at the site. The amount of water percolation through the UZ is low and difficult to measure directly, but local seepage into mined tunnels has been observed in the TCw. Past water seepage in the welded tuffs is recorded by widespread, thin (0.3 cm) coatings of calcite and silica on fracture surfaces and within cavities. Abundances of calcite and silica in the coatings were determined by X-ray microfluorescence mapping and subsequent multispectral image analysis of over 200 samples. The images were classified into constituent phases including opal-chalcedony-quartz (secondary silica) and calcite. In the TCw samples, the median calcite/silica ratio is 8; in the TSw samples within 35 m below the PTn, median calcite/silica falls to 2, perhaps reflecting an increase in soluble silica from the presence of glass in the nonwelded tuffs. In the deeper parts of the TSw, median calcite/silica reaches 100 and many samples contain no detectable secondary silica phase. Evaporation and changing pCO2 control precipitation of calcite from water percolating downward in the UZ, but precipitation of opal requires only evaporation. Calcite/silica ratios, therefore, can constrain the relative importance of evaporation in the UZ. Although calcite/silica values scatter widely within the TSw, reflecting the spatial variability of gas and water flow, average calcite/silica ratios increase with stratigraphic depth, indicating less evaporation at the deeper levels of the UZ. Coupled with the much smaller calcite/silica ratios

  9. Estimation of unsaturated zone liquid water flux at boreholes UZ No. 4, UZ No. 5, UZ No. 7, and UZ No. 13, Yucca Mountain, Nevada, from saturation and water potential profiles

    SciTech Connect

    Kwicklis, E.M.; Healy, R.W.; Flint, A.L.

    1993-12-31

    The unsaturated zone at Yucca Mountain, Nevada, is being investigated as a potential location for a high-level nuclear waste repository. Characterization of the liquid water flux and its spatial distribution under natural conditions provides estimates of the amount of water that could potentially contact the waste canisters and transport soluble radionuclides to the accessible environment. Estimates of ambient water flux may affect design requirements by indicating the degree to which reliance must be placed on engineered barriers or the waste-generated heat to keep the waste canisters dry.

  10. Formation of Zones with Maximum Supersonic Cavitation Intensity in Single-Component and Multicomponent Media

    NASA Astrophysics Data System (ADS)

    Bakhtin, B. I.; Ivashov, A. I.; Kuznetsov, A. V.; Skorokhodov, A. S.

    2016-05-01

    Experimental studies have been made on the formation of highly active cavitation zones in fluid media at high pressures (up to 6.5 MPa) and temperatures (up to 150°C) with the use of a high-power ultrasonic installation. It has been shown that attempts to increase the cavitation intensity in single-component and multicomponent media by increasing the power of the ultrasonic installation to above a certain limit lead to a strong degradation of the cavitation processes. This is due to the appearance of hydrodynamical flows generated by longitudinal vibrations of the installation radiator waveguide. Eliminating or weakening such flows makes it possible to increase markedly the efficiency of cavitation treatment by increasing the medium pressure (in the range of 0.5-1.5 MPa) and choosing the optimum ratio between the temperature of the medium and the power of the ultrasonic installation (specific acoustic power of the radiator). We recommend to use for the cavitation intensity index the acoustic activity of the cavitation zone (acoustic noise amplitude in the frequency range of 200 kHz-10 MHz), as well as its physical activity determined by the destruction rate of thin-layer indicators.

  11. Formation of Zones with Maximum Supersonic Cavitation Intensity in Single-Component and Multicomponent Media

    NASA Astrophysics Data System (ADS)

    Bakhtin, B. I.; Ivashov, A. I.; Kuznetsov, A. V.; Skorokhodov, A. S.

    2016-06-01

    Experimental studies have been made on the formation of highly active cavitation zones in fluid media at high pressures (up to 6.5 MPa) and temperatures (up to 150°C) with the use of a high-power ultrasonic installation. It has been shown that attempts to increase the cavitation intensity in single-component and multicomponent media by increasing the power of the ultrasonic installation to above a certain limit lead to a strong degradation of the cavitation processes. This is due to the appearance of hydrodynamical flows generated by longitudinal vibrations of the installation radiator waveguide. Eliminating or weakening such flows makes it possible to increase markedly the efficiency of cavitation treatment by increasing the medium pressure (in the range of 0.5-1.5 MPa) and choosing the optimum ratio between the temperature of the medium and the power of the ultrasonic installation (specific acoustic power of the radiator). We recommend to use for the cavitation intensity index the acoustic activity of the cavitation zone (acoustic noise amplitude in the frequency range of 200 kHz-10 MHz), as well as its physical activity determined by the destruction rate of thin-layer indicators.

  12. Variability of unsaturated zone water transport parameters: implications for hydrological modelling. 2. Predicted vs. in situ measurements and evaluation of methods

    NASA Astrophysics Data System (ADS)

    Ragab, R.; Cooper, J. D.

    1993-07-01

    Two methods to estimate the saturated and unsaturated hydraulic conductivity of soil were compared in a catchment in south-west England. The catchment consists of three land use domains — arable, permanent grass and woodland. The methods used were in situ measurements using a Guelph permeameter and the predictive model of Rawls and Brakensiek, which uses percentage of sand, percentage of clay and porosity as input. In grassland and woodland no significant differences were found between the mean saturated and unsaturated hydraulic conductivity estimated by the two methods. It is suggested that a significant difference found for the arable land is due to the effect of farming operations on soil permeability. On a catchment scale there were no significant differences between the methods. The results obtained using the predictive model are encouraging and worth further investigation. The advantages and disadvantages of the two methods are evaluated.

  13. The Effect of Dynamic Evaporation Rates on the Mobility of Pharmaceuticals in Unsaturated Environments

    NASA Astrophysics Data System (ADS)

    Normile, H.; Papelis, C.; Kibbey, T. C. G.

    2015-12-01

    The focus of this work was on investigating how dynamic rates of evaporation affect the fate and transport of pharmaceutical compounds in unsaturated porous media. The environmental processes of saturation and evaporation control local concentrations of contaminants in pore water of porous media. Specifically, the rate of evaporation can affect the identity and extent of solid formation of a pharmaceutical compound. A range of experiments with different evaporation rates were conducted on sand columns saturated with a solution of ciprofloxacin, a fluoroquinolone antibiotic. Experiments were designed to simulate increased and decreased pore-water concentrations of a compound due to evaporation and resaturation, respectively. Results suggest that varied rates of evaporation cause differences in compound adsorption behavior. This result has significant implications for understanding fate and transport within the unsaturated zone. Preliminary models exploring the impact on contaminant mobility are discussed.

  14. Modeling the transport of TiO2 nanoparticle aggregates in saturated and unsaturated granular media: effects of ionic strength and pH.

    PubMed

    Fang, Jing; Xu, Mei-jia; Wang, Deng-jun; Wen, Bei; Han, Jing-yi

    2013-03-01

    This study aims to explore the mechanisms governing the transport and retention kinetics of TiO(2) nanoparticle aggregates (NPAs) in flow-through columns of packed sand, particularly under unsaturated conditions. The study was carried out at different pHs (2.6, 7.1, and 9.6) and ionic strengths (ISs) (1.0, 10, and 50 mM). A two-site kinetic attachment model was used to describe transport behaviors of TiO(2) NPAs. At low ISs (i.e., 1.0 and 10 mM) and in neutral/alkaline conditions, high mobility of TiO(2) NPAs was observed in both saturated and unsaturated conditions. However, the retention of TiO(2) NPAs was substantially enhanced at the high IS (50 mM) and in extremely acidity condition (pH = 2.6), because of increased aggregation and straining of TiO(2) NPAs during their transport course. The breakthrough curves (BTCs) of TiO(2) NPAs under unsaturated and saturated conditions almost overlapped, suggesting that decreasing the water saturation did not enhance the retention of TiO(2) NPAs in sand columns. This was probably due to the repulsive interactions existed between negatively charged air-water and TiO(2) NPAs systems that resulted in unfavorable attachment conditions. The two-site kinetic attachment model provided a good description for the BTCs of TiO(2) NPAs both in saturated and unsaturated conditions. The fitted parameters could successfully explain the transport behaviors of TiO(2) NPAs under various solution chemistries. PMID:23276424

  15. Rapid imbibition of water in fractures within unsaturated sedimentary rock

    DOE PAGESBeta

    Cheng, Chu-Lin; Perfect, Edmund; Donnelly, B.; Bilheux, Hassina Z.; Tremsin, Anton S.; McKay, L. D.; Distefano, Victoria H.; Cai, J. C.; Santodonato, Louis J.

    2015-01-27

    The spontaneous imbibition of water and other liquids into gas-filled fractures in variably-saturated porous media is important in a variety of engineering and geological contexts. However, surprisingly few studies have investigated this phenomenon. In this paper, we present a theoretical framework for predicting the 1-dimensional movement of water into air-filled fractures within a porous medium based on early-time capillary dynamics and spreading over the rough surfaces of fracture faces. The theory permits estimation of sorptivity values for the matrix and fracture zone, as well as a dispersion parameter which quantifies the extent of spreading of the wetting front. Quantitative datamore » on spontaneous imbibition of water in unsaturated Berea sandstone cores were acquired to evaluate the proposed model. The cores with different permeability classes ranging from 50 to 500 mD and were fractured using the Brazilian method. Spontaneous imbibition in the fractured cores was measured by dynamic neutron radiography at the Neutron Imaging Prototype Facility (beam line CG-1D, HFIR), Oak Ridge National Laboratory. Water uptake into both the matrix and the fracture zone exhibited square-root-of-time behavior. The matrix sorptivities ranged from 2.9 to 4.6 mm s-0.5, and increased linearly as the permeability class increased. The sorptivities of the fracture zones ranged from 17.9 to 27.1 mm s-0.5, and increased linearly with increasing fracture aperture width. The dispersion coefficients ranged from 23.7 to 66.7 mm2 s-1 and increased linearly with increasing fracture aperture width and damage zone width. Both theory and observations indicate that fractures can significantly increase spontaneous imbibition in unsaturated sedimentary rock by capillary action and surface spreading on rough fracture faces. Fractures also increase the dispersion of the wetting front. In conclusion, further research is needed to investigate this phenomenon in other natural and engineered

  16. Rapid imbibition of water in fractures within unsaturated sedimentary rock

    NASA Astrophysics Data System (ADS)

    Cheng, C.-L.; Perfect, E.; Donnelly, B.; Bilheux, H. Z.; Tremsin, A. S.; McKay, L. D.; DiStefano, V. H.; Cai, J. C.; Santodonato, L. J.

    2015-03-01

    The spontaneous imbibition of water and other liquids into gas-filled fractures in variably-saturated porous media is important in a variety of engineering and geological contexts. However, surprisingly few studies have investigated this phenomenon. We present a theoretical framework for predicting the 1-dimensional movement of water into air-filled fractures within a porous medium based on early-time capillary dynamics and spreading over the rough surfaces of fracture faces. The theory permits estimation of sorptivity values for the matrix and fracture zone, as well as a dispersion parameter which quantifies the extent of spreading of the wetting front. Quantitative data on spontaneous imbibition of water in unsaturated Berea sandstone cores were acquired to evaluate the proposed model. The cores with different permeability classes ranging from 50 to 500 mD and were fractured using the Brazilian method. Spontaneous imbibition in the fractured cores was measured by dynamic neutron radiography at the Neutron Imaging Prototype Facility (beam line CG-1D, HFIR), Oak Ridge National Laboratory. Water uptake into both the matrix and the fracture zone exhibited square-root-of-time behavior. The matrix sorptivities ranged from 2.9 to 4.6 mm s-0.5, and increased linearly as the permeability class increased. The sorptivities of the fracture zones ranged from 17.9 to 27.1 mm s-0.5, and increased linearly with increasing fracture aperture width. The dispersion coefficients ranged from 23.7 to 66.7 mm2 s-1 and increased linearly with increasing fracture aperture width and damage zone width. Both theory and observations indicate that fractures can significantly increase spontaneous imbibition in unsaturated sedimentary rock by capillary action and surface spreading on rough fracture faces. Fractures also increase the dispersion of the wetting front. Further research is needed to investigate this phenomenon in other natural and engineered porous media.

  17. Influence of colloids on the attenuation and transport of phosphorus in alluvial gravel aquifer and vadose zone media.

    PubMed

    Pang, Liping; Lafogler, Mark; Knorr, Bastian; McGill, Erin; Saunders, Darren; Baumann, Thomas; Abraham, Phillip; Close, Murray

    2016-04-15

    Phosphorous (P) leaching (e.g., from effluents, fertilizers) and transport in highly permeable subsurface media can be an important pathway that contributes to eutrophication of receiving surface waters as groundwater recharges the base-flow of surface waters. Here we investigated attenuation and transport of orthophosphate-P in gravel aquifer and vadose zone media in the presence and absence of model colloids (Escherichia coli, kaolinite, goethite). Experiments were conducted using repacked aquifer media in a large column (2m long, 0.19m in diameter) and intact cores (0.4m long, 0.24m in diameter) of vadose zone media under typical field flow rates. In the absence of the model colloids, P was readily traveled through the aquifer media with little attenuation (up to 100% recovery) and retardation, and P adsorption was highly reversible. Conversely, addition of the model colloids generally resulted in reduced P concentration and mass recovery (down to 28% recovery), and increased retardation and adsorption irreversibility in both aquifer and vadose zone media. The degree of colloid-assisted P attenuation was most significant in the presence of fine material and Fe-containing colloids at low flow rate but was least significant in the presence of coarse gravels and E. coli at high flow rate. Based on the experimental results, setback distances of 49-53m were estimated to allow a reduction of P concentrations in groundwater to acceptable levels in the receiving water. These estimates were consistent with field observations in the same aquifer media. Colloid-assisted P attenuation can be utilized to develop mitigation strategies to better manage effluent applications in gravelly soils. To efficiently retain P within soil matrix and reduce P leaching to groundwater, it is recommended to select soils that are rich in iron oxides, to periodically disturb soil preferential flow paths by tillage, and to apply a low irrigation rate. PMID:26803685

  18. The Influence of Proposed Repository Thermal Load on MultiphaseFlow and Heat Transfer in the Unsaturated Zone of Yucca Mountain

    SciTech Connect

    Wu, Y.-S.; Mukhopadhyay, Sumit; Zhang, Keni; Bodvarsson, G.S.

    2006-02-28

    This paper investigates the impact of proposed repositorythermal-loading on mountain-scale flow and heat transfer in theunsaturated fractured rock of Yucca Mountain, Nevada. In this context, amodel has been developed to study the coupled thermal-hydrological (TH)processes at the scale of the entire Yucca Mountain. This mountain-scaleTH model implements the current geological framework and hydrogeologicalconceptual models, and incorporates the latest rock thermal andhydrological properties. The TH model consists of a two-dimensionalnorth-south vertical cross section across the entire unsaturated zonemodel domain and uses refined meshes near and around the proposedrepository block, based on the current repository design, drift layout,thermal loading scenario, and estimated current and future climaticconditions. The model simulations provide insights into thermallyaffected liquid saturation, gas- and liquid-phase fluxes, and elevatedwater and rock temperature, which in turn allow modelers to predict thechanges in water flux driven by evaporation/condensation processes, anddrainage between drifts.

  19. Interaction of Parallel Flow Mixing Zones and Calcium Carbonate Precipitation with High and Low Permeability Inclusions in Porous Media

    NASA Astrophysics Data System (ADS)

    Redden, G. D.; Fox, D. T.; Zundel, M.; Guo, L.; Lu, C.; Huang, H.; Fujita, Y.

    2012-12-01

    Engineered precipitation in porous media involves tight, non-linear coupling between reactant transport, mixing and reaction front propagation. We conducted an experimental campaign to investigate this coupling in homogenous and heterogeneous media where reactant mixing occurs across the interface between two solutions and a mineral precipitate (CaCO_{3}) is formed. Two solutions containing the components for precipitation of calcium carbonate (Ca^{2+} and HCO^{-}_{3}) were injected side-by-side into intermediate-scale flow cells packed with silica sand. Both of the individual influent solutions were undersaturated with respect to calcite. At the interface between the solutions, reactants mix by a combination of dispersive and diffusive transport, and calcium carbonate precipitation results. In homogeneous media we observed that transport across the interface decreased with time, as expected, and the volume-averaged rate of reaction decreased. When high and low permeability inclusions were placed in the path of the original mixing interface, the spatial and temporal evolution of the calcium carbonate precipitation zone showed more complicated coupling between transport and reaction kinetics. Low permeability inclusions (permeability 25X lower than the surrounding media) caused deflection of the mixing zone. Precipitate initially forms in the center of the mixing zone. Subsequently, lateral migration of the mixing/precipitation zone was observed that resulted in the inclusion being encapsulated by carbonate mineral. Precipitate that is subsequently exposed to the undersaturated calcium containing solution persists. For a high permeability inclusion (permeability 17X greater than the surrounding media) placed in the path of the mixing zone, the flow and mixing zone was initially focused and passed through the inclusion. Interestingly, enhanced dispersion was observed downstream of the inclusion, and the spatial extent of calcium carbonate precipitation was greater

  20. Pore scale imaging of transport in unsaturated flows

    NASA Astrophysics Data System (ADS)

    Jimenez-Martinez, J.; De Anna, P.; Turuban, R.; Tabuteau, H.; Le Borgne, T.; Meheust, Y.

    2013-12-01

    The unsaturated zone plays a key role in the transfer of chemical elements from the surface to the subsurface. Predicting the transport of chemical species through unsaturated porous media poses several challenges. The spatial distribution of wetting (water) and non-wetting (air) clusters focuses the water flow onto narrow and complex flow paths. The resulting velocity distribution is wider than that of saturated flow, and is controlled by the saturation degree. As saturation decreases, very low velocity zones in regions of trapped fluid coexist with connected fluid clusters with relatively high velocities. As a consequence, the dispersion of solute elements strongly depends on the saturation degree. We use a novel experimental setup to study the dependence on saturation of the longitudinal dispersion coefficient. The two-dimensional (2d) horizontal medium consists of cylindrical grains and is built using soft lithography. The joint injection of the two phases (wetting and non-wetting) provides a controlled homogeneous saturation in the medium. The simultaneous precise measurement of the flow field, the spatial distribution of wetting and non-wetting phases, and the 2d tracer concentration field, as well as breakthrough curves at different locations, are used to investigate the relationship between the flow field complexity and dispersion properties. The experimental results show a non-Fickian transport behavior, characterized by heavy tailed breakthrough curves and a longitudinal plume variance that does not scale linearly with time. We document and discuss the dependence of these transport properties on the saturation degree.

  1. Data from a thick unsaturated zone underlying Oro Grande and Sheep Creek washes in the western part of the Mojave Desert, near Victorville, San Bernardino County, California

    USGS Publications Warehouse

    Izbicki, John A.; Clark, Dennis A.; Pimental, Maria I.; Land, Michael; Radyk, John C.; Michel, Robert L.

    2000-01-01

    This report presents data on the physical properties of unsaturated alluvial deposits and on the chemical and isotopic composition of soil water and soil gas collected at 12 monitoring sites in the western part of the Mojave Desert, near Victorville, California. Sites were installed using the ODEX air-hammer method. Seven sites were located in the active channels of Oro Grande and Sheep Creek Washes. The remaining five sites were located away from the active washes. Most sites were drilled to a depth of about 100 feet below land surface; two sites were drilled to the water table almost 650 feet below land surface. Drilling procedures, lithologic and geophysical data, and site construction and instrumentation are described. Core material was analyzed for water content, bulk density, water potential, particle size, and water retention. The chemical composition of leachate from almost 1,000 subsamples of cores and cuttings was determined. Water extracted from selected subsamples of cores was analyzed for tritium and the stable isotopes of oxygen and hydrogen. Water from suction-cup lysimeters and soil-gas samples also were analyzed for chemical and isotopic composition. In addition, data on the chemical and isotopic composition of bulk precipitation from five sites and on ground water from two water-table wells are reported.

  2. Assessment of the influence of climate condition on a migration rate of the 90Sr in the unsaturated zone in the Kirov and Sverdlovsk Region, Russia

    NASA Astrophysics Data System (ADS)

    Kurinova, Natalia; Dediulina, Ekaterina

    2016-04-01

    In this research, the transport of 90Sr with unsaturated flow in the same geological section (0.5 m top soil, from 0.5 to 6.0 m sand) was taken under consideration in two regions: Kirov and Sverdlovsk Region, Russia. The modeling schematization assumed that the nuclide polluted top soil to the depth of 0.2 m and from this point are transported with infiltration of precipitation during 100 year. The modeling were conducted in Hydrus 1D. The climate classification based on the Budyko aridity index (Budyko 1958) was used to define climate differences between regions. According this classification climate in both are temperate continental but the biggest differences is in the wetting degree. The Kirov region has the aridity index about 0.70; there is overwatering conditions, which means that average annual precipitation exceeds the potential evapotranspiration. The Sverdlovsk region has the aridity index about 1.04; there is the optimal watering conditions. The results of modeling of the 90Sr migration process showed the transport dynamic dependence on wetting degree. At the end of the 100-year period, the 90Sr reached the depth of 1.3 m in Kirov region and 1.0 m in Sverdlovsk.

  3. Ground-water flow and effects of agricultural application of sewage sludge and other fertilizers on the chemical quality of sediments in the unsaturated zone and ground water near Platteville, Colorado, 1985-89

    USGS Publications Warehouse

    Gaggiani, N.G.

    1995-01-01

    From fall 1985 through 1989, 6,431 dry tons of anaerobic, digested, sewage sludge were applied as a fertilizer on about 1 square mile of sandy farm- land near Platteville, Colorado. Mean nitrite plus nitrate as nitrogen concentrations in the surficial aquifer increased during the period of sewage- sludge application. However, the effects of municipal sewage sludge applied to the soil in section 16 are difficult to ascertain because anhydrous ammonia and cattle and chicken manure were applied to section 16 prior to sewage-sludge application and anhydrous ammonia was applied during the period of sewage-sludge application. Mostly ammonia plus organic nitrogen was detected in the unsaturated zone while nitrite plus nitrate as nitrogen predominated in the surficial aquifer. The areas of largest concentrations of nitrite plus nitrate as nitrogen were in the northeastern and southwestern quarter sections os section 16. Changes in nitrite plus nitrate as nitrogen concentrations with depth and time were detected in water samples from the multilevel ground-water sampling devices in the surficial aquifer. Nitrogen probably entered the saturated zone in the irrigated areas and low temporarily ponded areas and moved to the northeast with water in the surficial aquifer.

  4. Vadose zone microbiology

    SciTech Connect

    Kieft, Thomas L.; Brockman, Fred J.

    2001-01-17

    The vadose zone is defined as the portion of the terrestrial subsurface that extends from the land surface downward to the water table. As such, it comprises the surface soil (the rooting zone), the underlying subsoil, and the capillary fringe that directly overlies the water table. The unsaturated zone between the rooting zone and the capillary fringe is termed the "intermediate zone" (Chapelle, 1993). The vadose zone has also been defined as the unsaturated zone, since the sediment pores and/or rock fractures are generally not completely water filled, but instead contain both water and air. The latter characteristic results in the term "zone of aeration" to describe the vadose zone. The terms "vadose zone," "unsaturated zone", and "zone of aeration" are nearly synonymous, except that the vadose zone may contain regions of perched water that are actually saturated. The term "subsoil" has also been used for studies of shallow areas of the subsurface immediately below the rooting zone. This review focuses almost exclusively on the unsaturated region beneath the soil layer since there is already an extensive body of literature on surface soil microbial communities and process, e.g., Paul and Clark (1989), Metting (1993), Richter and Markowitz, (1995), and Sylvia et al. (1998); whereas the deeper strata of the unsaturated zone have only recently come under scrutiny for their microbiological properties.

  5. An Integrated Modeling Analysis of Unsaturated Flow Patterns inFractured Rock

    SciTech Connect

    Wu, Yu-Shu; Lu, Guoping; Zhang, Keni; Pan, Lehua; Bodvarsson,Gudmundur S.

    2005-03-21

    Characterizing percolation patterns in unsaturated zones hasposed a greater challenge to numerical modeling investigations thancomparable saturated zone studies, because of the heterogeneous nature ofunsaturated media as well as the great number of variables impactingunsaturated zone flow. This paper presents an integrated modelingmethodology for quantitatively characterizing percolation patterns in theunsaturated zone of Yucca Mountain, Nevada, a proposed undergroundrepository site for storing high-level radioactive waste. It takes intoaccount the multiple coupled processes of air, water, heat flow andchemical isotopic transport in Yucca Mountain s highly heterogeneous,unsaturated fractured tuffs. The modeling approach integrates a widevariety of moisture, pneumatic, thermal, and isotopic geochemical fielddata into a comprehensive three-dimensional numerical model for modelinganalyses. Modeling results are examined against different types offield-measured data and then used to evaluate different hydrogeologicalconceptual models and their results of flow patterns in the unsaturatedzone. In particular, this integration model provides a much clearerunderstanding of percolation patterns and flow behavior through theunsaturated zone, both crucial issues in assessing repositoryperformance. The integrated approach for quantifying Yucca Mountain sflow system is also demonstrated to provide a comprehensive modeling toolfor characterizing flow and transport processes in complex subsurfacesystems.

  6. Media.

    ERIC Educational Resources Information Center

    Allen, Lee E., Ed.

    1974-01-01

    Intended for secondary English teachers, the materials and ideas presented here suggest ways to use media in the classroom in teaching visual and auditory discrimination while enlivening classes and motivating students. Contents include "Media Specialists Need Not Apply," which discusses the need for preparation of media educators with…

  7. Heterogeneity and Scaling in Geologic Media: Applications to Transport in the Vadose and Saturated Zones

    SciTech Connect

    Brown, Stephen R.

    2003-06-01

    Heterogeneity and Scaling in Geologic Media: Applications to Transport in the Vadose and Saturated Zones Stephen Brown, Gregory Boitnott, and Martin Smith New England Research In rocks and soils, the bulk geophysical and transport properties of the matrix and of fracture systems are determined by the juxtaposition of geometric features at many length scales. For sedimentary materials the length scales are: the pore scale (irregularities in grain surface roughness and cementation), the scale of grain packing faults (and the resulting correlated porosity structures), the scale dominated by sorting or winnowing due to depositional processes, and the scale of geomorphology at the time of deposition. We are studying the heterogeneity and anisotropy in geometry, permeability, and geophysical response from the pore (microscopic), laboratory (mesoscopic), and backyard field (macroscopic) scales. In turn these data are being described and synthesized for development of mathematical models. Eventually, we will perform parameter studies to explore these models in the context of transport in the vadose and saturated zones. We have developed a multi-probe physical properties scanner which allows for the mapping of geophysical properties on a slabbed sample or core. This device allows for detailed study of heterogeneity at those length scales most difficult to quantify using standard field and laboratory practices. The measurement head consists of a variety of probes designed to make local measurements of various properties, including: gas permeability, acoustic velocities (compressional and shear), complex electrical impedance (4 electrode, wide frequency coverage), and ultrasonic reflection (ultrasonic impedance and permeability). We can thus routinely generate detailed geophysical maps of a particular sample. With the exception of the acoustic velocity, we are testing and modifying these probes as necessary for use on soil samples. As a baseline study we have been

  8. The Role of Natural Organic Matter and Mineral Colloids in the Transport of Contaminants through Heterogeneous Vadose-Zone Environments

    SciTech Connect

    James Saiers, Yale University; Joseph Ryan, University of Colorado

    2009-01-31

    Our research was guided by a key objective of the Environmental Management Science Program (EMSP), which is to improve conceptual and predictive models for contaminant movement in complex vadose zone environments. In this report, increases in the understanding of colloidcontaminant interactions, colloid mobilization, and colloid deposition within unsaturated soils are cited as requisite needs for predicting contaminant fate and distribution in the vadose zone. We addressed these needs by pursuing three key goals: 1. Identify the mechanisms that govern OM and mineral-colloid reaction and transport in heterogeneous, unsaturated porous media; 2. Quantify the role of OM and mineral colloids in scavenging and facilitating the transport of contaminants of concern to DOE; and 3. Develop and test a mathematical model suitable for simulating the movement of OM- and colloid-associated contaminants through heterogeneous, unsaturated porous media.

  9. Microbial Activity and Precipitation at Solution-Solution Mixing Zones in Porous Media -- Subsurface Biogeochemical Research

    SciTech Connect

    Colwell, Frederick; Wildenschild, Dorthe; Wood, Brian; Gerlach, Robin; Mitchell, Andrew; Redden, George

    2014-08-29

    The goal for this research was to understand how best to add compounds to receptive microbial communities in porous media in order to achieve optimal calcite precipitation in a volumetrically significant space and to understand the physiological health of the cells that are responsible for the calcite precipitation. The specific objectives were to: (1) develop better tools for visually examining biofilms in porous media and calcium carbonate precipitation being mediated by microbes in porous media, and (2) demonstrate the effectiveness of using that tool within a flow cell model system.

  10. A field technique to measure the tortuosity and sorption-affected porosity for gaseous diffusion of materials in the unsaturated zone with experimental results from near Barnwell, South Carolina

    NASA Astrophysics Data System (ADS)

    Kreamer, David K.; Weeks, Edwin P.; Thompson, Glenn M.

    1988-03-01

    A tracer experiment was conducted at the commercial low-level nuclear waste disposal site near Barnwell, South Carolina, to test a new method for determining the tortuosity and sorption-affected porosity for gaseous diffusion transport of materials in the Unsaturated zone. Two tracers, CBrClF2 and SF6, were released at constant rates of 105 and 3.3 ng/s, respectively, from permeation devices, which were placed in short screened sections in access holes. Soil gas was sampled from 15 piezometers located at various distances from the sources by sequentially pumping 60-160 mL of gas from the piezometers into a dual-column gas chromatograph located at the test site. The CBrClF2 concentration data obtained from several of the piezometers were analyzed by use of type curves for a continuous point source in an areally extensive medium bounded above and below by planar no-flow boundaries. The tortuosity of the geologic unit tested, an eolian sand, was determined to be about 0.4, and the sorption-affected porosity to be 0.22. The tortuosity value is plausible, but the sorption-affected porosity value is substantially less than that computed from the drained porosity, particularly if adjustments are made for retardation due to solution of the tracer in the liquid phase and sorption on the solid phase. The SF6 data could not be reliably analyzed.

  11. Age dating ground water by use of chlorofluorocarbons (CCl{sub 3}F and CCl{sub 2}F{sub 2}), and distribution of chlorofluorocarbons in the unsaturated zone, Snake River Plain aquifer, Idaho National Engineering Laboratory, Idaho

    SciTech Connect

    Busenberg, E.; Weeks, E.P.; Plummer, L.N.; Bartholomay, R.C.

    1993-04-01

    Detectable concentrations of chlorofluorocarbons (CFC`s) were observed in ground water and unsaturated-zone air at the Idaho National Engineering Laboratory (INEL) and vicinity. The recharge ages of waters were determined to be from 4 to more than 50 years on the basis of CFC concentrations and other environmental data; most ground waters have ages of 14 to 30 years. These results indicate that young ground water was added at various locations to the older regional ground water (greater than 50 years) within and outside the INEL boundaries. The wells drilled into the Snake River Plain aquifer at INEL sampled mainly this local recharge. The Big Lost River, Birch Creek, the Little Lost River, and the Mud Lake-Terreton area appear to be major sources of recharge of the Snake River Plain aquifer at INEL. An average recharge temperature of 9.7{plus_minus}1.3{degrees}C (degrees Celsius) was calculated from dissolved nitrogen and argon concentrations in the ground waters, a temperature that is similar to the mean annual soil temperature of 9{degrees}C measured at INEL. This similarity indicates that the aquifer was recharged at INEL and not at higher elevations that would have cooler soil temperatures than INEL. Soil-gas concentrations at Test Area North (TAN) are explained by diffusion theory.

  12. Flow and transport through unsaturated fractured rock: An overview

    NASA Astrophysics Data System (ADS)

    Evans, Daniel D.; Rasmussen, Todd C.; Nicholson, Thomas J.

    Groundwater flow and contaminant transport through the unsaturated zone continue to receive attention as former nuclear weapons development sites are being characterized for determining decommissioning options, and geologic sites are being considered for deep disposal of nuclear and hazardous waste. The ability to make decisions with regard to cleanup, site suitability, and anticipated performance of disposal or storage facilities is dependent upon the characterization and modeling of unsaturated flow and transport features, events, and processes. Hazardous materials may be mobilized by infiltrating water and move downward to affect groundwater resources. These contaminants may also move upward or laterally by capillary movement or as vapor to the accessible environment. Substantial experience exists with respect to near-surface partially saturated porous media, traditionally the domain of the soil scientists and geotechnical engineers, but does not exist for fractured rock in either near-surface or deep, complex, unsaturated systems that are now being characterized and modeled. The ability to represent these complex systems composed of both a matrix and a fracture component is being tested through a variety of field experiments and comparisons to natural analogues. The present focus is on evaluating conceptual flow and transportmodels and quantifying the spatial and temporal parameters for these models using laboratory and field methods, and environmental tracer analyses. Modeling of these dynamic and transient systems has followed two paths, porous equivalency and discrete fracture models. In general, characterization methods and modelingare in the confirmation stage with the greatest lack of knowledge being the interaction between fracture and matrix properties for flow and transport.

  13. Magnetic resonance imaging analysis on the in-situ mixing zone of CO2 miscible displacement flows in porous media

    NASA Astrophysics Data System (ADS)

    Song, Yongchen; Yang, Wenzhe; Wang, Dayong; Yang, Mingjun; Jiang, Lanlan; Liu, Yu; Zhao, Yuechao; Dou, Binlin; Wang, Zhiguo

    2014-06-01

    The in-situ mixing zone represents dynamic characteristics of CO2 miscible displacement flows, which is important for carbon dioxide enhanced oil recovery (CO2-EOR) projects. However, the migration characteristics of the in-situ mixing zone under reservoir conditions has been neither well studied nor fully understood. The in-situ mixing zone with the flowing mixture of supercritical CO2 and n-decane (nC10) was investigated by using a magnetic resonance imaging apparatus at a reservoir condition of 8.5 MPa and 37.8 °C in porous media. The experimental results showed that the CO2-frontal velocity was larger than the mixing-frontal velocity. The mixing zone length was linearly declined in the miscible displacement process. And the declining rate of the mixing zone length was increased with injection rate. It indicates that the mixing zone length is not constant in a vertically stable CO2 misible displacement and a volume contraction due to phase behavior effects may occur. Then, an error function based on the convection-dispersion equation was fitted with CO2 miscible displacement experiments. The error function was well fitted both at a series of fixed core positions and a series of fixed displacement times. Furthermore, the longitudinal dispersion coefficients (Klx and Klt) and the longitudinal Peclet numbers (Ped and PeL) were quantified from the fitting results. The evolutions of the longitudinal dispersion coefficient were reduced along the displacement time. And the declining rate was increased with injection rate. And with proceeding, the longitudinal dispersion coefficient was tending towards stability and constant. But the evolutions of the longitudinal Peclet numbers were increased along the displacement time. And the increasing rate was increased with injection rate.

  14. FINAL REPORT. CONTROL OF BIOLOGICALLY ACTIVE DEGRADATION ZONES BY VERTICAL HETEROGENEITY: APPLICATIONS IN FRACTURED MEDIA

    EPA Science Inventory

    The key objective of this research was to determine the distribution of biologically active contaminant degradation zones in a fractured, subsurface medium with respect to vertical heterogeneities. Our expectation was that
    hydrogeological properties would determine the size, d...

  15. Hydrological and Hydrochemical Characterization of Fault Zones in Crystalline Media: Implications for Groundwater Fluxes

    NASA Astrophysics Data System (ADS)

    Roques, C.; Aquilina, L.; Bour, O.; Dewandel, B.

    2014-12-01

    Fault zones are heterogeneities that may greatly influence groundwater flow in crystalline regions. The quantification of fluxes, the origin of water and geochemical processes associated to groundwater flow in such context remain not well understood. This study mainly concerns a large-scale multidisciplinary field experiments performed on a specific site in Brittany (Saint-Brice en Coglès, France) where a permeable fault zone was identified at depth (200 m). The main objectives here are to constrain both fluxes dynamic and water sources involved during different seasonal regimes. We demonstrate that the fault zone allows the discharge of regional groundwater at the watershed outlet. Using specific hydro-geophysical measurements (Heat Pulse Flow Meter), we estimate a natural discharge rate between 150 and 200 m3/d. The fault zone presents different geochemical signatures related to changes in hydrologic regime. They are linked to transient fluxes enhancement from different reservoirs. During the low hydrologic regimes, water with high resident time flows along the fault zone, with a contribution of inter-glacial origin (recharge temperature of 7°C deduced from noble gases interpretation). Water trapped in a low-permeability domain is mobilized to the fault zone and/or large-scale circulation loops are involved. During the high hydrologic regimes, modern water predominantly ensures the recharge of the system at a local scale. Results are compared to regional observations in the Armoricain Massif in order to establish mechanisms responsible for recharge and migration of groundwater at the basement scale.

  16. Prediction of Diffusion Coefficients in Porous Media using Tortuosity Factors Based on Interfacial Areas

    SciTech Connect

    Saripalli, Kanaka P.; Serne, R. Jeffrey; Meyer, Philip D.; McGrail, B. Peter

    2002-08-01

    Determination of aqueous phase diffusion coefficients of solutes through porous media is essential for understanding and modeling contaminant transport. Prediction of diffusion coefficients in both saturated and unsaturated zones requires knowledge of tortuosity and constrictivity factors. No methods are available for the direct measurement of these factors, which are empirical in their definition. In this paper, a new definition for the tortuosity factor is proposed, as the real to ideal interfacial area ratio. We define the tortuosity factor for saturated porous media (ts) as the ratio S/So (specific surface of real porous medium to that of an idealized capillary bundle). For unsaturated media, tortuosity factor (ta) is defined as aaw/aaw,o (ratio of the specific air-water interfacial area of real and the corresponding idealized porous medium). This tortuosity factor is suitably measured using sorptive tracers (e.g., nitrogen adsorption method) for saturated media and interfacial tracers for unsaturated media. A model based on this new definition of tortuosity factors, termed the Interfacial Area Ratio (IAR) model, is presented for the prediction of diffusion coefficients as a function of the degree of water saturation. Diffusion coefficients and diffusive resistances measured in a number of saturated and unsaturated granular porous media, for solutes in dilute aqueous solutions, agree well with the predictions of the IAR model. A comparison of permeability of saturated sands estimated based on ts and the same based on the Kozeny-Carman equation confirm the usefulness of the ts parameter as a measure of tortuosity.

  17. Sensitivity analysis of unsaturated flow and contaminant transport with correlated parameters

    NASA Astrophysics Data System (ADS)

    Pan, Feng; Zhu, Jianting; Ye, Ming; Pachepsky, Yakov A.; Wu, Yu-Shu

    2011-02-01

    SummaryThis study conducts sensitivity and uncertainty analysis for predicting unsaturated flow and contaminant transport in a layered heterogeneous system. The objectives of this work are to: (1) examine the effects of parameter correlations on the sensitivity of unsaturated flow and contaminant transport and (2) assess the relative contributions of parameter uncertainties to the uncertainties of flow and transport at each hydrogeologic layer. Using the unsaturated zone (UZ) of Yucca Mountain (YM) in Nevada, USA, as an example, the study considers cases of independent and correlated parameters. A sampling-based regression method is used, when the model input parameters are independent, and a decomposition method is used for the correlated case. When the parameters are independent, the uncertainty in permeability has the largest contribution to the uncertainties in simulated percolation flux and mass of the reactive tracer arriving at the water table. For the percolation flux, the second largest contribution is from the van Genuchten α; the sorption coefficient of the reactive tracer is the second most important parameter for the tracer mass arrival uncertainty. The sensitivity to the sorption coefficient is larger in the layers of devitrified and zeolitic tuffs than in the layers of vitric tuff. Contributions of the uncertainties in van Genuchten n and porosity to the percolation flux and tracer transport uncertainties are larger in the case of correlated parameters compared with the case of independent parameters due to the correlations of n and porosity with the van Genuchten α and permeability, respectively. These results illustrate the significant effects of parameter correlations on the sensitivity and uncertainty of unsaturated flow and transport. The findings are of significance in facilitating future characterizations to reduce the parameter uncertainties and associated predictive uncertainties of flow and contaminant transport in unsaturated fractured

  18. Use of O2 consumption and CO2 production in kinetic cells to delineate pyrite oxidation-carbonate buffering and microbial respiration in unsaturated media.

    PubMed

    Lee, Eung Seok; Hendry, M Jim; Hollings, P

    2003-09-01

    Identifying zones of sulphide oxidation and carbonate buffering is important in the development of a management plan for mine waste-rock piles. In this study, we used a kinetic cell technique to measure rates of O2 consumption and CO2 production in low sulphide (<0.12 wt.% S), low inorganic carbon (<0.20 wt.% C(inorganic)), gneissic waste rock and associated organic-rich lake sediment (0.7 wt.% C(organic)), and forest soil (1.4 wt.% C(organic)) collected from the Key Lake uranium mine in Saskatchewan, Canada. Solid chemistry, stable carbon isotope, pore water sulphate concentration data, and stoichiometric considerations indicated that O2 consumption and CO2 production were constrained by microbial respiration in the lake sediment and forest soil and by pyrite oxidation-carbonate buffering in the gneissic waste rock. Mean ratios of molar CO2 production to O2 consumption rates were 0.5 for lake sediment, 0.7 for forest soil, and 0.2 for gneissic waste rock. The different O2/CO2 ratios suggested that O2-CO2 monitoring may provide a practical tool for identifying the zones of microbial respiration and pyrite oxidation-carbonate buffering in mine waste-rock piles. Rates of O2 consumption and CO2 production were about one order of magnitude greater in lake sediment than in gneissic waste rock, indicating that microbial respiration would exert a control on the distribution of O2 and CO2 gas in waste-rock piles constructed upon the dewatered lake sediments. PMID:12935950

  19. Use of O 2 consumption and CO 2 production in kinetic cells to delineate pyrite oxidation-carbonate buffering and microbial respiration in unsaturated media

    NASA Astrophysics Data System (ADS)

    Lee, Eung Seok; Hendry, M. Jim; Hollings, P.

    2003-09-01

    Identifying zones of sulphide oxidation and carbonate buffering is important in the development of a management plan for mine waste-rock piles. In this study, we used a kinetic cell technique to measure rates of O 2 consumption and CO 2 production in low sulphide (<0.12 wt.% S), low inorganic carbon (<0.20 wt.% C inorganic), gneissic waste rock and associated organic-rich lake sediment (0.7 wt.% C organic), and forest soil (1.4 wt.% C organic) collected from the Key Lake uranium mine in Saskatchewan, Canada. Solid chemistry, stable carbon isotope, pore water sulphate concentration data, and stoichiometric considerations indicated that O 2 consumption and CO 2 production were constrained by microbial respiration in the lake sediment and forest soil and by pyrite oxidation-carbonate buffering in the gneissic waste rock. Mean ratios of molar CO 2 production to O 2 consumption rates were 0.5 for lake sediment, 0.7 for forest soil, and 0.2 for gneissic waste rock. The different O 2/CO 2 ratios suggested that O 2-CO 2 monitoring may provide a practical tool for identifying the zones of microbial respiration and pyrite oxidation-carbonate buffering in mine waste-rock piles. Rates of O 2 consumption and CO 2 production were about one order of magnitude greater in lake sediment than in gneissic waste rock, indicating that microbial respiration would exert a control on the distribution of O 2 and CO 2 gas in waste-rock piles constructed upon the dewatered lake sediments.

  20. In situ unsaturated zone water stable isotope (2H and 18O) measurements in semi-arid environments: a soil water balance

    NASA Astrophysics Data System (ADS)

    Gaj, Marcel; Beyer, Matthias; Koeniger, Paul; Wanke, Heike; Hamutoko, Josefina; Himmelsbach, Thomas

    2016-02-01

    Stable isotopes (deuterium, 2H, and oxygen-18, 18O) of soil water were measured in the field using a liquid water isotope analyzer (tunable off-axis integrated cavity output spectroscope, OA-ICOS, LGR) and commercially available soil gas probes (BGL-30, UMS, Munich) in the semi-arid Cuvelai-Etosha Basin (CEB), Namibia. Results support the applicability of an in situ measurement system for the determination of stable isotopes in soil pore water. High spatial and temporal resolution was achieved in the study area with reasonable accuracy and measurements were in agreement with laboratory-based cryogenic vacuum extraction and subsequent cavity ring-down laser spectroscopic isotope analysis (CRDS, L2120-i, Picarro Inc.). After drift and span correction of the in situ isotope data, precision for over 140 measurements taken during two consecutive field campaigns (June and November 2014) was 1.8 and 0.48 ‰ for δ2H and δ18O, respectively. Mean measurement trueness is determined using quality check standards and was 5 and 0.3 ‰ for δ2H and δ18O, respectively. The isotope depth profiles are used quantitatively to calculate a soil water balance. The contribution of transpiration to total evapotranspiration ranged between 72 and 92 %. Shortly after a rain event, the contribution of transpiration was much lower, at 35 to 50 %. Potential limitations of such an in situ system are related to environmental conditions which could be minimized by using a temperature-controlled chamber for the laser spectrometer. Further, the applicability of the system using previously oven-dried soil material might be limited by physicochemical soil properties (i.e., clay minerals). Uncertainty in the in situ system is suggested to be reduced by improving the calibration procedure and further studying fractionation effects influencing the isotope ratios in the soil water, especially at low water contents. Furthermore, the influence of soil-respired CO2 on isotope values within the root zone

  1. Stabilized unsaturated polyesters

    NASA Technical Reports Server (NTRS)

    Vogl, O.; Borsig, E. (Inventor)

    1985-01-01

    An unsaturated polyester, such as propylene glycolmaleic acid phthalic acid prepolymer dissolved in styrene is interpolymerized with an ultraviolet absorber and/or an antioxidant. The unsaturated chain may be filled with H or lower alkyl such as methyl and tertiary alkyl such as tertiary butyl. A polymer stable to exposure to the outdoors without degradation by ultraviolet radiation, thermal and/or photooxidation is formed.

  2. Rapid imbibition of water in fractures within unsaturated sedimentary rock

    SciTech Connect

    Cheng, Chu-Lin; Perfect, Edmund; Donnelly, B.; Bilheux, Hassina Z.; Tremsin, Anton S.; McKay, L. D.; Distefano, Victoria H.; Cai, J. C.; Santodonato, Louis J.

    2015-01-27

    The spontaneous imbibition of water and other liquids into gas-filled fractures in variably-saturated porous media is important in a variety of engineering and geological contexts. However, surprisingly few studies have investigated this phenomenon. In this paper, we present a theoretical framework for predicting the 1-dimensional movement of water into air-filled fractures within a porous medium based on early-time capillary dynamics and spreading over the rough surfaces of fracture faces. The theory permits estimation of sorptivity values for the matrix and fracture zone, as well as a dispersion parameter which quantifies the extent of spreading of the wetting front. Quantitative data on spontaneous imbibition of water in unsaturated Berea sandstone cores were acquired to evaluate the proposed model. The cores with different permeability classes ranging from 50 to 500 mD and were fractured using the Brazilian method. Spontaneous imbibition in the fractured cores was measured by dynamic neutron radiography at the Neutron Imaging Prototype Facility (beam line CG-1D, HFIR), Oak Ridge National Laboratory. Water uptake into both the matrix and the fracture zone exhibited square-root-of-time behavior. The matrix sorptivities ranged from 2.9 to 4.6 mm s-0.5, and increased linearly as the permeability class increased. The sorptivities of the fracture zones ranged from 17.9 to 27.1 mm s-0.5, and increased linearly with increasing fracture aperture width. The dispersion coefficients ranged from 23.7 to 66.7 mm2 s-1 and increased linearly with increasing fracture aperture width and damage zone width. Both theory and observations indicate that fractures can significantly increase spontaneous imbibition in unsaturated sedimentary rock by capillary action and surface spreading on rough fracture faces. Fractures also increase the dispersion of the wetting front. In conclusion, further research is needed to investigate this phenomenon

  3. The influence of substrate and electron acceptor availability on bioactive zone dynamics in porous media

    NASA Astrophysics Data System (ADS)

    Yolcubal, Irfan; Dorn, Jonathan G.; Maier, Raina M.; Brusseau, Mark L.

    2003-11-01

    Two approaches were used to investigate the influence of dissolved oxygen (DO) and substrate availability on the formation and dynamics of "bioactive zones" in a water-saturated porous medium. A bioactive zone is defined as a region where a microbial community is sufficiently active to metabolize bioavailable substrates. In the first approach, microbial activity was characterized by monitoring the spatial and temporal variability of DO and aqueous substrate (salicylate and naphthalene) concentrations during miscible-displacement experiments. In the second approach, microbial activity was monitored using multiple fiber optics emplaced in the porous medium to detect luminescence produced by Pseudomonas putida RB1353, a bioluminescent reporter organism that produces light when salicylate (an intermediate of naphthalene degradation) is present. The results of both approaches show that the location and size of the bioactive zones were influenced by in situ DO and substrate availability. When DO was not a limiting factor (i.e., lower substrate input concentrations), the bioactive zone encompassed the entire column, with the majority of the microbial activity occurring between the inlet and midpoint. However, as the availability of DO became limiting for the higher substrate input experiments, the size of the bioactive zone shrank and was ultimately limited to the proximity of the column inlet.

  4. Geohydrology of the unsaturated zone and simulated time of arrival of landfill leachate at the water table, municipal solid waste landfill facility, US Army Air Defense Artillery Center and Fort Bliss, El Paso County, Texas

    USGS Publications Warehouse

    Frenzel, Peter F.; Abeyta, Cynthia G.

    1999-01-01

    The U.S. Air Defense Artillery Center and Fort Bliss Municipal Solid Waste Landfill Facility (MSWLF) is located about 10 miles northeast of downtown El Paso, Texas. The landfill is built on the Hueco Bolson, a deposit that yields water to five public-supply wells within 1.1 miles of the landfill boundary on all sides. The bolson deposits consist of lenses and mixtures of sand, clay, silt, gravel, and caliche. The unsaturated zone at the landfill is about 300 feet thick. The Hydrologic Evaluation of Landfill Performance (HELP) and the Multimedia Exposure Assessment Model for Evaluating the Land Disposal of Wastes (MULTIMED) computer models were used to simulate the time of first arrival of landfill leachate at the water table. Site-specific data were collected for model input. At five sites on the landfill cover, hydraulic conductivity was measured by an in situ method; i