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Ofer Dahan - One of the best experts on this subject based on the ideXlab platform.
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Combining cross-hole geophysical and Vadose Zone monitoring systems for Vadose Zone characterization at industrial contaminated sites
2016Co-Authors: Natalia Fernandez De Vera, Ofer Dahan, Jean Beaujean, Pierre Jamin, David Caterina, Marnik Vanclooster, Alain Dassargues, Frédéric Nguyen, Serge BrouyèreAbstract:Abstract. Water flow and solute transport through a fractured Vadose Zone underneath an industrial contaminated site in Belgium were studied with a new methodological concept. The Vadose Zone Experimental Setup (VZES) combines a Vadose Zone monitoring system (VMS) with cross-borehole geophysics. The VMS provides continuous chemical and hydraulic information at multiple depths in the Vadose Zone. When combining such information with multidirectional subsurface imaging from geophysical measurements, flow and transport can be characterized at a scale that covers the spatial variability of the subsurface. The setup was installed on site and monitoring was carried out under natural recharge conditions. Results reveal quick rises in water content as a response to rainfall events in the upper and intermediate part of the Vadose Zone (down to 3.65 m depth). Macropore, micropore, matrix and preferential flow mechanisms are identified at these depth ranges. At greater depths, flow dynamics is slower and dominated by matrix flow. The governance of water flow mechanisms at different directions is controlled by the heterogeneous distribution of geological materials. Results from sampled waters across the Vadose Zone reveal that the chemistry of water collected from matrix is different from that collected from fractures. In addition, analysis of heavy metals indicates that Ni is leaching across the Vadose Zone, and its release might be a consequence of pyrite oxidation from backfilled materials. Results obtained from VZES indicate that the combination of different techniques providing in situ quantitative and qualitative information improves conceptual models of flow and transport in a heterogeneous subsurface.
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Vadose Zone characterisation at industrial contaminated sites
2015Co-Authors: Natalia Fernandez De Vera, Ofer Dahan, Marnik Vanclooster, Alain Dassargues, Frédéric Nguyen, Serge BrouyèreAbstract:An important challenge faced by environmental practitioners is the estimation of the impact of contamination that is transported from the source of contamination to soil and groundwater at industrial sites. Specifically, quantification of contaminant flux in the Vadose Zone is challenging due partly to the heterogeneity of the complex porous medium and the preferential flow. Contaminant flux estimations are essential to better establish risk assessment of soil and groundwater as well as to support the selection of remedial measures. Several methods have been developed for contaminant flux estimations in the Vadose Zone. These methodologies are either based on modelling, on experimental approaches, or on the combination of both, and have been developed principally in the context of agricultural purposes. However, the applicability of such techniques is questioned when it comes to their application to industrial sites, due to differences in depth of investigation, soil origin, contamination and sources. An overview of contaminant flux measurement techniques, together with a potential alternative for improving characterisation techniques and contaminant flux measurement in the Vadose Zone is presented in this bulletin. The Vadose Zone experimental setup consists of the combination of the Vadose Zone Monitoring System (VMS) and cross-hole geophysics.
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Vadose Zone studies at an industrial contaminated site: the Vadose Zone monitoring system and cross-hole geophysics
The EGU General Assembly, 2014Co-Authors: Natalia Fernandez De Vera, Ofer Dahan, Jean Beaujean, Pierre Jamin, Marnik Vanclooster, Frédéric Nguyen, Serge BrouyèreAbstract:In order to improve risk characterization and remediation measures for soil and groundwater contamination, there is a need to improve in situ Vadose Zone characterization. However, most available technologies have been developed in the context of agricultural soils. Such methodologies are not applicable at industrial sites, where soils and contamination differ in origin and composition. In addition, most technologies are applicable only in the first meters of soils, leaving deeper Vadose Zones with lack of information, in particular on field scale heterogeneity. In order to overcome such difficulties, a Vadose Zone experiment has been setup at a former industrial site in Belgium. Industrial activities carried out on site left a legacy of soil and groundwater contamination in BTEX, PAH, cyanide and heavy metals. The experiment comprises the combination of two techniques: the Vadose Zone Monitoring System (VMS) and cross-hole geophysics. The VMS allows continuous measurements of water content and temperature at different depths of the Vadose Zone. In addition, it provides the possibility of pore water sampling at different depths. The system is formed by a flexible sleeve containing monitoring units along its depth which is installed in a slanted borehole. The flexible sleeve contains three types of monitoring units in the Vadose Zone: Time Domain Transmissometry (TDT), which allows water content measurements; Vadose Sampling Ports (VSP), used for collecting water samples coming from the matrix; the Fracture Samplers (FS), which are used for retrieving water samples from the fractures. Cross-hole geophysics techniques consist in the injection of an electrical current using electrodes installed in vertical boreholes. From measured potential differences, detailed spatial patterns about electrical properties of the subsurface can be inferred. Such spatial patterns are related with subsurface heterogeneities, water content and solute concentrations. Two VMS were installed in two slanted boreholes on site, together with four vertical boreholes containing electrodes for geophysical measurements. Currently the site is being monitored under natural recharge conditions. Initial results show the reaction of the Vadose Zone to rainfall events, as well as chemical evolution of soil water with depth.
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Water percolation through a clayey Vadose Zone
Journal of Hydrology, 2012Co-Authors: S Baram, Daniel Kurtzman, Ofer DahanAbstract:Summary Heavy clay soils are regarded as less permeable due to their low saturated hydraulic conductivities, and are perceived as safe for the construction of unlined or soil-lined waste lagoons. Water percolation dynamics through a smectite-dominated clayey Vadose Zone underlying a dairy waste lagoon, waste channel and their margins was investigated using three independent Vadose-Zone monitoring systems. The monitoring systems, hosting 22 TDR sensors, were used for continuous measurements of the temporal variation in Vadose Zone water-content profiles. Results from 4 years of continuous measurements showed quick rises in sediment water content following rain events and temporal wastewater overflows. The percolation pattern indicated dominance of preferential flow through a desiccation-crack network crossing the entire clay sediment layer (depth of 12 m). High water-propagation velocities (0.4–23.6 m h −1 ) were observed, indicating that the desiccation-crack network remains open and serves as a preferential flow pathway year-round, even at high sediment water content (∼0.50 m 3 m −3 ). The natural formation of desiccation-crack networks at the margins of waste lagoons induces rapid infiltration of raw waste to deep sections of the Vadose Zone, bypassing the sediment’s most biogeochemically active parts, and jeopardizing groundwater quality.
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Solute transport in the Vadose Zone and groundwater during flash floods
Water Resources Research, 2011Co-Authors: Yanai Amiaz, Shaul Sorek, Yehouda Enzel, Ofer DahanAbstract:events were investigated in the lower reach of the Kuiseb River, Namibia, and in controlled column experiments. Simultaneous measurements of water level and electrical conductivity of the ood water in the stream channel and in the groundwater together with variations in the Vadose Zone water content, temperature, and pressure proles allowed a detailed analysis of the various mechanisms governing solute transport in the subsurface during ash oods. The results indicated that on the land surface, ash oods emit, at their wetting fronts, instantaneous compression waves that propagate downward through the unsaturated Zone to the water table. These compression waves generate abrupt solute-displacement events in the groundwater immediately after the arrival of the ood on the land surface, long before deep percolation and groundwater recharge begin. Each ood event launches into the Vadose Zone a wetting front that propagates down through the Vadose Zone and recharges the groundwater upon arrival at the water table. Therst wetting front of each ood season leaches out soluble salts that have accumulated in the Vadose Zone during the dry season. However, water percolation through the unsaturated Zone does not leach out the entire soluble salt capacity of the sediment, even if percolation takes place under high water-head ooding conditions for long periods. The incomplete leaching of the unsaturated Zone by the percolating water releases soluble salts into the groundwater during every recharge event as a result of the rise of the water table into the Vadose Zone; this process results in a temporal increase of the groundwater electrical conductivity (EC).
Anderson L. Ward - One of the best experts on this subject based on the ideXlab platform.
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Vadose Zone Transport Field Study: Summary Report
2006Co-Authors: Anderson L. Ward, Glendon W. Gee, Mark E. Conrad, William Daily, J Fink, Vicky L. Freedman, Gary M. Hoversten, Jason M. Keller, Ernest L. Majer, Christopher J. MurrayAbstract:From FY 2000 through FY 2003, a series of Vadose Zone transport field experiments were conducted as part of the U.S. Department of Energy’s Groundwater/Vadose Zone Integration Project Science and Technology Project, now known as the Remediation and Closure Science Project, and managed by the Pacific Northwest National Laboratory (PNNL). The series of experiments included two major field campaigns, one at a 299-E24-11 injection test site near PUREX and a second at a clastic dike site off Army Loop Road. The goals of these experiments were to improve our understanding of Vadose Zone transport processes; to develop data sets to validate and calibrate Vadose Zone flow and transport models; and to identify advanced monitoring techniques useful for evaluating flow-and-transport mechanisms and delineating contaminant plumes in the Vadose Zone at the Hanford Site. This report summarizes the key findings from the field studies and demonstrates how data collected from these studies are being used to improve conceptual models and develop numerical models of flow and transport in Hanford’s Vadose Zone. Results of these tests have led to a better understanding of the Vadose Zone. Fine-scale geologic heterogeneities, including grain fabric and lamination, were observed to have a strong effect on the large-scale behavior of contaminant plumes, primarily through increased lateral spreading resulting from anisotropy. Conceptual models have been updated to include lateral spreading and numerical models of unsaturated flow and transport have revised accordingly. A new robust model based on the concept of a connectivity tensor was developed to describe saturation-dependent anisotropy in strongly heterogeneous soils and has been incorporated into PNNL’s Subsurface Transport Over Multiple Phases (STOMP) simulator. Application to field-scale transport problems have led to a better understanding plume behavior at a number of sites where lateral spreading may have dominated waste migration (e.g. BC Cribs and Trenches). The improved models have been also coupled with inverse models and newly-developed parameter scaling techniques to allow estimation of field-scale and effective transport parameters for the Vadose Zone. The development and utility of pedotransfer functions for describing fine-scale hydrogeochemical heterogeneity and for incorporating this heterogeneity into reactive transport models was explored. An approach based on grain-size statistics appears feasible and has been used to describe heterogeneity in hydraulic properties and sorption properties, such as the cation exchange capacity and the specific surface area of Hanford sediments. This work has also led to the development of inverse modeling capabilities for time-dependent, subsurface, reactive transport with transient flow fields using an automated optimization algorithm. In addition, a number of geophysical techniques investigated for their potential to provide detailed information on the subtle changes in lithology and bedding surfaces; plume delineation, leak detection. High-resolution resistivity is now being used for detecting saline plumes at several waste sites at Hanford, including tank farms. Results from the field studies and associated analysis have appeared in more than 46 publications generated over the past 4 years. These publications include test plans and status reports, in addition to numerous technical notes and peer reviewed papers.
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Vadose Zone Transport Field Study: Status Report
2001Co-Authors: Glendon W. Gee, Anderson L. WardAbstract:Studies were initiated at the Hanford Site to evaluate the process controlling the transport of fluids in the Vadose Zone and to develop a reliable database upon which Vadose-Zone transport models can be calibrated. These models are needed to evaluate contaminant migration through the Vadose Zone to underlying groundwaters at Hanford. A study site that had previously been extensively characterized using geophysical monitoring techniques was selected in the 200 E Area. Techniques used previously included neutron probe for water content, spectral gamma logging for radionuclide tracers, and gamma scattering for wet bulk density. Building on the characterization efforts of the past 20 years, the site was instrumented to facilitate the comparison of nine Vadose-Zone characterization methods: advanced tensiometers, neutron probe, electrical resistance tomography (ERT), high-resolution resistivity (HRR), electromagnetic induction imaging (EMI), cross-borehole radar, and cross-borehole seismic.
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Vadose Zone Transport Field Study: Status Report
2001Co-Authors: Glendon W. Gee, Anderson L. WardAbstract:Studies were initiated at the Hanford Site to evaluate the process controlling the transport of fluids in the Vadose Zone and to develop a reliable database upon which Vadose-Zone transport models can be calibrated. These models are needed to evaluate contaminant migration through the Vadose Zone to underlying groundwaters at Hanford. A study site that had previously been extensively characterized using geophysical monitoring techniques was selected in the 200 E Area. Techniques used previously included neutron probe for water content, spectral gamma logging for radionuclide tracers, and gamma scattering for wet bulk density. Building on the characterization efforts of the past 20 years, the site was instrumented to facilitate the comparison of nine Vadose-Zone characterization methods: advanced tensiometers, neutron probe, electrical resistance tomography (ERT), high-resolution resistivity (HRR), electromagnetic induction imaging (EMI), cross-borehole radar (XBR), and cross-borehole seismic (XBS). Soil coring was used to obtain soil samples for analyzing ionic and isotopic tracers
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Vadose Zone Transport Field Study: FY 2002 Test Plan
2001Co-Authors: Anderson L. Ward, Glendon W. GeeAbstract:The primary objective of the Vadose Zone Transport Field Study is to obtain hydrologic, geophysical, and geochemical data from controlled field studies to reduce the uncertainty in Vadose-Zone conceptual models and to facilitate the calibration of numerical models for water flow and contaminant transport through Hanford's heterogeneous Vadose Zone. A secondary objective is to evaluate advanced, cost-effective characterization methods with the potential to assess changing conditions in the Vadose Zone, particularly as surrogates of currently undetectable high-risk contaminants. The study is designed to assure the measurement of flow-and-transport properties in the same soil volume, a pre-requisite for developing techniques for extrapolating parameters derived from investigations at clean representative sites to contaminated sites with minimal characterization.
Glendon W. Gee - One of the best experts on this subject based on the ideXlab platform.
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Vadose Zone Transport Field Study: Summary Report
2006Co-Authors: Anderson L. Ward, Glendon W. Gee, Mark E. Conrad, William Daily, J Fink, Vicky L. Freedman, Gary M. Hoversten, Jason M. Keller, Ernest L. Majer, Christopher J. MurrayAbstract:From FY 2000 through FY 2003, a series of Vadose Zone transport field experiments were conducted as part of the U.S. Department of Energy’s Groundwater/Vadose Zone Integration Project Science and Technology Project, now known as the Remediation and Closure Science Project, and managed by the Pacific Northwest National Laboratory (PNNL). The series of experiments included two major field campaigns, one at a 299-E24-11 injection test site near PUREX and a second at a clastic dike site off Army Loop Road. The goals of these experiments were to improve our understanding of Vadose Zone transport processes; to develop data sets to validate and calibrate Vadose Zone flow and transport models; and to identify advanced monitoring techniques useful for evaluating flow-and-transport mechanisms and delineating contaminant plumes in the Vadose Zone at the Hanford Site. This report summarizes the key findings from the field studies and demonstrates how data collected from these studies are being used to improve conceptual models and develop numerical models of flow and transport in Hanford’s Vadose Zone. Results of these tests have led to a better understanding of the Vadose Zone. Fine-scale geologic heterogeneities, including grain fabric and lamination, were observed to have a strong effect on the large-scale behavior of contaminant plumes, primarily through increased lateral spreading resulting from anisotropy. Conceptual models have been updated to include lateral spreading and numerical models of unsaturated flow and transport have revised accordingly. A new robust model based on the concept of a connectivity tensor was developed to describe saturation-dependent anisotropy in strongly heterogeneous soils and has been incorporated into PNNL’s Subsurface Transport Over Multiple Phases (STOMP) simulator. Application to field-scale transport problems have led to a better understanding plume behavior at a number of sites where lateral spreading may have dominated waste migration (e.g. BC Cribs and Trenches). The improved models have been also coupled with inverse models and newly-developed parameter scaling techniques to allow estimation of field-scale and effective transport parameters for the Vadose Zone. The development and utility of pedotransfer functions for describing fine-scale hydrogeochemical heterogeneity and for incorporating this heterogeneity into reactive transport models was explored. An approach based on grain-size statistics appears feasible and has been used to describe heterogeneity in hydraulic properties and sorption properties, such as the cation exchange capacity and the specific surface area of Hanford sediments. This work has also led to the development of inverse modeling capabilities for time-dependent, subsurface, reactive transport with transient flow fields using an automated optimization algorithm. In addition, a number of geophysical techniques investigated for their potential to provide detailed information on the subtle changes in lithology and bedding surfaces; plume delineation, leak detection. High-resolution resistivity is now being used for detecting saline plumes at several waste sites at Hanford, including tank farms. Results from the field studies and associated analysis have appeared in more than 46 publications generated over the past 4 years. These publications include test plans and status reports, in addition to numerous technical notes and peer reviewed papers.
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Vadose Zone Transport Field Study: Status Report
2001Co-Authors: Glendon W. Gee, Anderson L. WardAbstract:Studies were initiated at the Hanford Site to evaluate the process controlling the transport of fluids in the Vadose Zone and to develop a reliable database upon which Vadose-Zone transport models can be calibrated. These models are needed to evaluate contaminant migration through the Vadose Zone to underlying groundwaters at Hanford. A study site that had previously been extensively characterized using geophysical monitoring techniques was selected in the 200 E Area. Techniques used previously included neutron probe for water content, spectral gamma logging for radionuclide tracers, and gamma scattering for wet bulk density. Building on the characterization efforts of the past 20 years, the site was instrumented to facilitate the comparison of nine Vadose-Zone characterization methods: advanced tensiometers, neutron probe, electrical resistance tomography (ERT), high-resolution resistivity (HRR), electromagnetic induction imaging (EMI), cross-borehole radar, and cross-borehole seismic.
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Vadose Zone Transport Field Study: Status Report
2001Co-Authors: Glendon W. Gee, Anderson L. WardAbstract:Studies were initiated at the Hanford Site to evaluate the process controlling the transport of fluids in the Vadose Zone and to develop a reliable database upon which Vadose-Zone transport models can be calibrated. These models are needed to evaluate contaminant migration through the Vadose Zone to underlying groundwaters at Hanford. A study site that had previously been extensively characterized using geophysical monitoring techniques was selected in the 200 E Area. Techniques used previously included neutron probe for water content, spectral gamma logging for radionuclide tracers, and gamma scattering for wet bulk density. Building on the characterization efforts of the past 20 years, the site was instrumented to facilitate the comparison of nine Vadose-Zone characterization methods: advanced tensiometers, neutron probe, electrical resistance tomography (ERT), high-resolution resistivity (HRR), electromagnetic induction imaging (EMI), cross-borehole radar (XBR), and cross-borehole seismic (XBS). Soil coring was used to obtain soil samples for analyzing ionic and isotopic tracers
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Vadose Zone Transport Field Study: FY 2002 Test Plan
2001Co-Authors: Anderson L. Ward, Glendon W. GeeAbstract:The primary objective of the Vadose Zone Transport Field Study is to obtain hydrologic, geophysical, and geochemical data from controlled field studies to reduce the uncertainty in Vadose-Zone conceptual models and to facilitate the calibration of numerical models for water flow and contaminant transport through Hanford's heterogeneous Vadose Zone. A secondary objective is to evaluate advanced, cost-effective characterization methods with the potential to assess changing conditions in the Vadose Zone, particularly as surrogates of currently undetectable high-risk contaminants. The study is designed to assure the measurement of flow-and-transport properties in the same soil volume, a pre-requisite for developing techniques for extrapolating parameters derived from investigations at clean representative sites to contaminated sites with minimal characterization.
Thomas L. Kieft - One of the best experts on this subject based on the ideXlab platform.
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Encyclopedia of Environmental Microbiology - Vadose Zone Microbiology
Encyclopedia of Environmental Microbiology, 2003Co-Authors: Fred J. Brockman, S. N. Bradley, Thomas L. KieftAbstract: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 Sylviamore » et al. (1998); whereas the deeper strata of the unsaturated Zone have only recently come under scrutiny for their microbiological properties.« less
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Vadose Zone Microbiology: Science and Applications
2002Co-Authors: Fred J. Brockman, Stephen D. Bradley, Thomas L. KieftAbstract:Brockman FJ, SN Bradley and TL Kieft. 2002. Vadose Zone microbiology. In Encyclopedia of Environmental Microbiology, volume 6, pp. 3236-3246. John Wiley and Sons, New York.
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Microbial Ecology of the Vadose Zone
1999Co-Authors: Thomas L. KieftAbstract:Studies in the last decade have demonstrated the presence of microorganisms in a variety of subsurface terrestrial environments, including the unsaturated layer (Vadose Zone) lying between surface soil and underlying groundwater. Viable microorganisms have been detected in Vadose Zone sediments and rocks. Populations of microorganisms are generally larger in relatively thin unsaturated Zones of mesic environments; Vadose Zones in arid regions can be tens to hundreds of meters thick and generally have very low microbial abundance and activities. Buried soils (paleosols) can have larger microbial populations than sediments that have not undergone soil development. Although Vadose Zone environments are generally moist, the thin water films limit the transport of nutrients. Recharge rates can be as low as a few micrometers per year or less, resulting in minuscule nutrient fluxes. Opportunities for transport of microbes into deep, low-recharge unsaturated layers are minimal; thus, microbes in these environments may be descendants of populations that existed when the sediments or rocks were buried. The thin water films and scattered distribution of microorganisms limit cell-cell interactions, and thus Vadose Zone microbes may not function as true microbial communities. Vadose Zone microbial activities may influence the fate and transport of subsurface contaminants and should be considered in the design and performance of hazardous waste repositories.
Jan W. Hopmans - One of the best experts on this subject based on the ideXlab platform.
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Vadose Zone Journal: A Decade of Multidisciplinary Research
Vadose Zone Journal, 2013Co-Authors: Martinus Th. Van Genuchten, Jan W. HopmansAbstract:Ten years ago we welcomed you to the first issue of Vadose Zone Journal (VZJ). As the first two editors of VZJ, we very much remember the enormous excitement about finally having a dedicated outlet designed to bring much-needed direction to Vadose Zone research ([van Genuchten, 2002][1]; [Hopmans et
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Deep Vadose Zone hydrology demonstrates fate of nitrate in eastern San Joaquin Valley
California Agriculture, 2005Co-Authors: Thomas Harter, Jan W. Hopmans, Yuksel S. Onsoy, Katrin Heeren, Michelle Denton, Gary S. Weissmann, William R. HorwathAbstract:The sustainability of water resources is key to continued prosperity in the San Joaquin Valley and California. The Vadose Zone is an often-ignored layer of wet but unsaturated sediments between the land surface and the water table. It plays an important role in groundwater recharge and in controlling the flux and attenuation of nitrate and other potential groundwater contaminants. In a former orchard at the UC Kearney Research and Extension Center, we investigated the processes that control the movement of water, nitrate and other contaminants through the deep Vadose Zone. These processes were found to be controlled by the alluvial sedimentary geology of the Vadose Zone, which is highly heterogeneous. This heterogeneity should be considered when interpreting soil and deep Vadose Zone monitoring data and assessing of the leaching potential of agricultural chemicals. The transport of contaminants through the Vadose Zone may be significantly faster than previously assumed, while denitrification is likely limited or insignificant in the oxic, alluvial Vadose Zone of the eastern San Joaquin Valley.
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Vadose Zone Hydrology - Emerging Measurement Techniques for Vadose Zone Characterization
Vadose Zone Hydrology, 1999Co-Authors: Jan W. Hopmans, Jan M. H. HendrickxAbstract:Variables and parameters required to characterize soil water flow and solute transport are often measured at different spatial scales from those for which they are needed. This poses a problem since results from field and laboratory measurements at one spatial scale are not necessarily valid for application at another. Herein lies a challenge that Vadose Zone hydrologists are faced with. For example, Vadose Zone studies can include flow at the groundwater-unsaturated Zone as well as at the soil surface-atmosphere interface at either one specific location or representing an entire field or landscape unit. Therefore, Vadose Zone measurements should include techniques that can monitor at large depths and that characterize landsurface processes. On the other end of the space spectrum, microscopic laboratory measurement techniques are needed to better understand fundamental flow and transport mechanisms through observations of pore-scale geometry and fluid flow. The Vadose Zone Hydrology (VZH) Conference made very clear that there is an immediate need for such microscopic information at fluid-fluid and solid-fluid interfaces, as well as for methodologies that yield information at the field/landscape scale. The need for improved instrumentation was discussed at the ASA-sponsored symposium on “Future Directions in Soil Physics” by Hendrickx (1994) and Hopmans (1994). Soil physicists participating in the 1994-1999 Western Regional Research Project W-188 (1994) focused on “improved characterization and quantification of flow and transport processes in soils,” and prioritized the need for development and evaluation of new instrumentation and methods of data anlysis to further improve characterization of water and solute transport. The regional project documents the critical need for quantification of water flow and solute transport in heterogeneous, spatially variable field soils, specifically to address preferential and accelerated contaminant transport. Cassel and Nielsen (1994) describe the contributions in computed tomography (CT) using x-rays or magnetic resonance imaging (MRI) as “an awakening,” and they envision these methodologies to become an integral part of Vadose Zone research programs. The difference in size between measurement and application scales poses a dilemma for the Vadose Zone hydrologist.
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Vadose Zone hydrology cutting across disciplines
1999Co-Authors: Marc B Parlange, Jan W. HopmansAbstract:The Vadose Zone is the region between ground level and the upper limits of soil fully saturated with water. Hydrology in the Zone is complex: nonlinear physical, chemical, and biological interactions all affect the transfer of heat, mass, and momentum between the atmosphere and the water table. This book takes an interdiscipliary approach to Vadose Zone hydrology, bringing together insights from soil science, hydrology, biology, chemistry, physics, and instrumentation design. The chapters present state-of-the-art research, focusing on new frontiers in theory, experiment, and management of soils. The collection addresses the full range of processes, from the pore-scale to field and landscape scales.
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Developments in Vadose Zone soil solution extraction
1997Co-Authors: Jan W. Hopmans, Graham E. Fogg, R. F DenisonAbstract:The study of water migration and contaminant transport in soils is of fundamental importance in hydrologic science. Movement of agrochemicals (nitrates, atrazine) and industrial solvents (TeE, carbontetrachloride) to the groundwater is of great public concern. In order for these chemicals to reach the groundwater, they must pass through the Vadose Zone. Thus, in order to predict travel times of contaminants toward the groundwater or to understand the underlying transport process, we need to characterize and sample the unsaturated Zone. The need for an economical, readily available monitoring system with a broad range of applications is required by the practicing groundwater scientist and Vadose Zone hydrologist, given the growing recognition of the interdependence of the unsaturated Zone and saturated Zone processes. At present, there are few, if any, cost effective and practical field monitoring devices which incorporate the sophisticated sampling and data acquisition array necessary for representative monitoring of the Vadose Zone. As concern for a save environment and groundwater quality increases, the importance of an accurate soil hydraulic description of the combined unsaturated-saturated porous system is increasingly recognized in the fields of environmental engineering and groundwater hydrology. With this wider interest, the spatial scale of interest has shifted to dimensions as large as a watershed, and to depths from the rooting Zone to the groundwater. This trend in increasing larger spatial scales of the Vadose Zone brings along with it the presence of increasing soil heterogeneity within the considered system. Therefore, methodologies need to be developed that allow for a rapid and accurate characterization for the soil hydraulic properties and its spatial variability. The objectives of the WRC-sponsered research was to develop a single sampling unit which can be used to sample soil solution, but at the same time monitors continuously the soil water potential. The second objective was to demonstrate the potential application of this combined tensiometer-soil soluton extraction probe to estimate in situ the soil water retention and unsaturated hydraulic conductivity functions.
