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  • 1
    Electronic Resource
    Electronic Resource
    Two-Well Test Method for Determining Hydraulic Properties of Aquifers (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 35 (1997), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A steady-state test to determine the hydraulic properties of an aquifer is presented. The test uses an injection-extraction well-pair to establish a two-dimensional, steady-state flow field in the tested region. At least one observation well is needed to measure the hydraulic head within the flow field. Depending on the number of observation wells, a single-observation-well method or a distance-head method is used to analyze the head data. Two field examples demonstrate the potential application of the test. The field experiments were done at the U.S. Department of Energy Hanford site near Richland, Washington. The two-well test procedure described in this work provides a useful alternative for characterizing aquifers while deploying in situ ground-water remediation systems. One of the most attractive features of this test, especially at contaminated aquifers, is that there is no water to dispose. The test is simple and economical, and it also avoids several other limitations associated with typical pumping or slug tests.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1997.tb00136.x
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Demonstration of Combined Zero-Valent Iron and Electrical Resistance Heating for In Situ Trichloroethene Remediation (2011)
    American Chemical Society
    Details
    Publication Date: 2011-06-15
    Print ISSN: 0013-936X
    Electronic ISSN: 1520-5851
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Published by American Chemical Society
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  • 3
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    Determination of Water Saturation in Relatively Dry Porous Media Using Gas-Phase Tracer Tests (2011)
    Soil Science Society of America (SSSA)
    Details
    Publication Date: 2011-05-01
    Description: Soil desiccation (drying), induced by dry air injection and moist air extraction, is a potentially robust remediation process to slow migration of inorganic or radionuclide contaminants through the vadose zone. The application of gas-phase partitioning tracer tests has been proposed as a means to estimate initial water volumes and to monitor the progress of the desiccation process at pilot tests and field sites. In this study, tracer tests were conducted in porous medium columns with various water saturations using SF6 as the conservative tracer and trichlorofluoromethane and difluoromethane as the water-partitioning tracers. For porous media with minimal silt or organic matter fractions, tracer tests provided reasonable saturation estimates for saturations close to zero. For sediments with significant silt or organic matter fractions, however, tracer tests only provided satisfactory results when the water saturation was greater than 0.1 to 0.2. For drier conditions, the apparent tracer retardation increased due to air-soil sorption, which is not included in traditional retardation coefficients derived from advection-dispersion equations accounting only for air-water partitioning and water-soil sorption. Based on these results, gas-phase partitioning tracer tests may be used to determine initial water volumes in sediments, provided that the initial water saturations are sufficiently large. Tracer tests are not suitable for quantifying moisture content in relatively dry sediments, however, especially if significant amounts of organic matter or silt are present.
    Electronic ISSN: 1539-1663
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Soil Science Society of America (SSSA)
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  • 4
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    Pore-Water Extraction from Unsaturated Porous Media: Intermediate-Scale Laboratory Experiments and Simulations (2014)
    Soil Science Society of America (SSSA)
    Details
    Publication Date: 2014-08-12
    Description: 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 to recognize the limitations of the technique. Column experiments were designed to investigate the relations between imposed suctions, water saturations, and water extraction. 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 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 condition 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.
    Electronic ISSN: 1539-1663
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Soil Science Society of America (SSSA)
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  • 5
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    Monitoring Vadose Zone Desiccation with Geophysical Methods (2013)
    Soil Science Society of America (SSSA)
    Details
    Publication Date: 2013-05-18
    Description: Soil desiccation was recently field tested as a potential vadose zone remediation technology. Desiccation removes water from the vadose zone and significantly decreases the aqueous-phase permeability of the desiccated zone, thereby decreasing movement of moisture and contaminants. The two- and three-dimensional distribution of moisture content reduction with time provides valuable information for desiccation operations and for determining when treatment goals have been reached. This type of information can be obtained through the use of geophysical methods. Neutron moisture logging, cross-hole electrical resistivity tomography, and cross-hole ground-penetrating radar approaches were evaluated with respect to their ability to provide effective spatial and temporal monitoring of desiccation during a treatability study conducted in the vadose zone of the USDOE Hanford site in the state of Washington.
    Electronic ISSN: 1539-1663
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Soil Science Society of America (SSSA)
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  • 6
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    Determination of Water Saturation Using Gas Phase Partitioning Tracers and Time-Lapse Electrical Conductivity Measurements (2013)
    Soil Science Society of America (SSSA)
    Details
    Publication Date: 2013-05-18
    Description: Water saturation is an important indicator of contaminant distribution and plays a governing role in contaminant transport within the vadose zone. Understanding the water saturation distribution is critical for both remediation and contaminant flux monitoring in unsaturated environments. In this work, we propose and demonstrate a method of remotely determining water saturation levels using gas phase partitioning tracers and time-lapse bulk electrical conductivity measurements. The theoretical development includes the partitioning chemistry for the tracers we demonstrate (ammonia and carbon dioxide), as well as a review of the petrophysical relationship governing how these tracers influence bulk conductivity. We also investigate methods of utilizing secondary information provided by electrical conductivity breakthrough magnitudes induced by the tracers. We test the method on clean, well characterized, intermediate-scale sand columns under controlled conditions. Results demonstrate the capability to accurately monitor gas breakthrough curves along the length of the column according to the corresponding electrical conductivity response, and to adequately determine partitioning coefficients, leading to accurate water saturation estimates. This work is motivated by the need to develop effective characterization and monitoring techniques for contaminated deep vadose zone environments, and provides a proof-of-concept toward uniquely characterizing and monitoring water saturation levels at the field scale and in three-dimensions using electrical resistivity tomography.
    Electronic ISSN: 1539-1663
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Soil Science Society of America (SSSA)
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  • 7
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    Characterization and Remediation of Chlorinated Volatile Organic Contaminants in the Vadose Zone (2013)
    Soil Science Society of America (SSSA)
    Details
    Publication Date: 2013-11-16
    Description: Contamination of vadose-zone systems by chlorinated solvents is widespread and poses significant potential risk to human health through impacts on groundwater quality and vapor intrusion. Soil vapor extraction (SVE) is the presumptive remedy for such contamination and has been used successfully for innumerable sites; however, SVE operations typically exhibit reduced mass-removal effectiveness at some point due to the impact of poorly accessible contaminant mass and associated mass-transfer limitations. Assessment of SVE performance and closure is currently based on characterizing contaminant mass discharge associated with the vadose-zone source and its impact on groundwater or vapor intrusion. These issues are addressed in this overview, with a focus on summarizing recent advances in our understanding of the transport, characterization, and remediation of chlorinated solvents in the vadose zone. The evolution of contaminant distribution with time and the associated impacts on remediation efficiency are discussed, as is potential impact of persistent sources on groundwater quality and vapor intrusion. In addition, alternative methods for site characterization and remediation are addressed.
    Electronic ISSN: 1539-1663
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Soil Science Society of America (SSSA)
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  • 8
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    Geochemical and Geophysical Changes during Ammonia Gas Treatment of Vadose Zone Sediments for Uranium Remediation (2012)
    Soil Science Society of America (SSSA)
    Details
    Publication Date: 2012-11-28
    Description: Low water content sediments were treated with NH 3 gas to evaluate changes in U mobility as a potential field remediation method for vadose zone contamination. Injection of NH 3 gas created high dissolved NH 3 concentrations that followed equilibrium behavior. High NH 3 concentration led to an increase in pH from 8.0 to 11 to 13, depending on the water content and NH 3 concentration. The increase in pore water pH resulted in a large increase in pore water cations and anions from mineral-phase dissolution. Minerals showing the greatest dissolution included montmorillonite, muscovite, and kaolinite. Pore water ion concentrations then decreased with time. Simulations based on initial pore water ion concentrations indicated that quartz, chrysotile, calcite, diaspore, hematite, and Na-boltwoodite (hydrous U silicate) should precipitate. Electrical resistivity and induced polarization tomography (ERT/IP) was able to nonintrusively track these NH 3 partitioning, dissolution, and precipitations processes through changes in conductivity and chargeability. Ammonia treatment significantly decreases the amount of U present as adsorbed and aqueous species in field-contaminated sediments. In contrast, sediments containing a large fraction of U associated with carbonates generally showed little change. Uranium leaching from sediments containing high Na-boltwoodite decreased significantly by NH 3 treatment, but x-ray absorption near-edge structure/extended x-ray absorption fine structure showed no change in the Na-boltwoodite concentration. Therefore, NH 3 treatment of contaminated sediment acts to decrease the highly mobile aqueous and adsorbed U by incorporation into precipitates and appears to decrease mobility of some existing U precipitates (Na-boltwoodite) as a result of mineral coating.
    Electronic ISSN: 1539-1663
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Soil Science Society of America (SSSA)
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  • 9
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    Field-Scale Assessment of Desiccation Implementation for Deep Vadose Zone Contaminants (2012)
    Soil Science Society of America (SSSA)
    Details
    Publication Date: 2012-11-28
    Description: Desiccation of the vadose zone has the potential to reduce the flux of contaminants to underlying groundwater by removing moisture and decreasing the water relative permeability of the desiccated zone. However, data to evaluate implementation of desiccation are needed before desiccation can be considered as a potential remedy. Implementation of desiccation was field tested by injecting dry nitrogen gas to a target treatment zone and monitoring the spatial and temporal progress of the drying process. Aqueous waste discharges to disposal cribs approximately 50 yr ago distributed water and contaminants, primarily technetium-99 and nitrate, within the 100-m deep vadose zone at the test site. The test was conducted adjacent to one of the former disposal cribs in a contaminated portion of the vadose zone dominated by fine sands with lenses of loamy sand. Desiccation removed over 18,000 kg of water from the test zone within the 151-d active desiccation period and reduced volumetric moisture content over 1300 m 3 of soil with values lower than 0.01 (m 3 m –3 ) in 68 m 3 . The lateral and vertical distribution of drying from the injection well was influenced by the subsurface heterogeneity with initial drying in higher permeability zones. However, over time, desiccation also occurred in the initially wetter, lower permeability lenses.
    Electronic ISSN: 1539-1663
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Soil Science Society of America (SSSA)
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  • 10
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    Effects of Porous Medium Heterogeneity on Vadose Zone Desiccation: Intermediate-Scale Laboratory Experiments and Simulations (2012)
    Soil Science Society of America (SSSA)
    Details
    Publication Date: 2012-11-28
    Description: Soil desiccation (drying), involving water evaporation induced by dry gas injection, is a potentially robust vadose zone remediation process to limit contaminant transport through the vadose zone. A series of four intermediate-scale flow cell experiments was conducted in homogeneous and simple layered heterogeneous porous medium systems to investigate the effects of heterogeneity on desiccation of unsaturated porous media. The permeability ratios of porous medium layers ranged from about 5 to almost 2 orders of magnitude. The insulated flow cell was equipped with 20 humidity and temperature sensors while a dual-energy system was used to determine water saturations at various times. The multiphase code STOMP was used to simulate the desiccation process. For the layered systems, results show that injected dry gas flowed predominantly in the higher permeability layer and delayed water removal from the lower permeability material. For the configurations tested, water vapor diffusion from the lower to the higher permeability zone was considerable over the duration of the experiments, resulting in much larger relative humidity values of the outgoing air than based on permeability ratios alone. Acceptable numerical matches with the experimental data were obtained when an extension of the saturation-capillary pressure relation below the residual water saturation was used. The agreements between numerical and experimental results suggest that the correct physics is implemented in the simulator.
    Electronic ISSN: 1539-1663
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Soil Science Society of America (SSSA)
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