Deep Vadose Zone Contaminant Flux Evaluation at the Hanford BY-Cribs Site Using Forward and Imposed Concentration Modeling Approaches

Oostrom, Martinus; Truex, Michael J.; Rockhold, Mark; Johnson, Timothy C.

doi:10.1007/s40710-017-0272-5

Cited by 7 publications

(7 citation statements)

References 28 publications

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“…Physical and hydraulic properties that were assigned to these units for flow and transport modeling are listed in Table 1. These parameters were based on prior modeling efforts and site characterization data (Oostrom et al 2013(Oostrom et al , 2017Rockhold et al 2018a, b). The parameters K sxx , K syy , and K szz are the saturated hydraulic conductivities in the x-, y-, and zdirections, respectively.…”

Section: Site Descriptionmentioning

confidence: 99%

“…Contamination of unsaturated sediments and underlying aquifer systems is a problem at many industrial waste sites (Oostrom et al 2017;Kuras et al 2016). The interactions between biophysical and geochemical processes that occur within the highly heterogeneous vadose zone are difficult to visualize, which limits our understanding of how subsurface features and processes affect contaminant transport and fate (Binley et al 2015).…”

Section: Introductionmentioning

confidence: 99%

“…Both vertical and horizontal flow through a PA may be affected by the adjacent low-permeability layers, which may cause increased lateral flow. Sparsity of well data may also make it difficult to delineate the extent of a PA, and to monitor remediation efforts (Carroll et al 2009;Oostrom et al 2017).…”

Section: Introductionmentioning

confidence: 99%

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Groundwater characterization and monitoring at a complex industrial waste site using electrical resistivity imaging

et al. 2020

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A contaminated industrial waste site in Washington State (USA) containing buried, metallic-waste storage tanks, pipes, and wells, was evaluated to determine the feasibility of monitoring groundwater remediation activities associated with an underlying perched aquifer system using electrical resistivity tomography. The perched aquifer, located ~65 m below ground surface and ~10 m above the regional water table, contains high concentrations of nitrate, uranium, and other contaminants of concern from past tank leaks and intentional releases of wastes to surface disposal sites. The extent of the perched water aquifer is not well known, and the effectiveness of groundwater extraction for contaminant removal is uncertain, so supplemental characterization and monitoring technologies are being evaluated. Numerical simulations of subsurface flow and contaminant transport were performed with a highly resolved model of the hydrogeologic system and waste site infrastructure, and these simulations were used as the physical basis for electrical resistivity tomography modeling. The modeling explicitly accounted for metallic infrastructure at the site. The effectiveness of using surface electrodes versus surface and horizontal subsurface electrodes, for imaging groundwater extraction from the perched water aquifer, was investigated. Although directional drilling is a mature technology, its use for electrode emplacement in the deep subsurface under a complex industrial waste site via horizontal wells has not yet been demonstrated. Results from this study indicate that using horizontal subsurface electrode arrays could significantly improve the ability of electrical resistivity tomography to image deep subsurface features and monitor remediation activities under complex industrial waste sites.

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Section: Site Descriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Groundwater characterization and monitoring at a complex industrial waste site using electrical resistivity imaging

et al. 2020

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“…For the time‐lapse simulations, the inverse modeling only solved for changes within the saturated zone. Assuming annual recharge remains relatively constant (Oostrom et al ), it is justified at this scale that the spatial delineation and precipitation inputs affecting bulk conductivity within the saturated zone also remain constant. To further constrain the time‐lapse inversion, decreases in conductivity within the saturated zone were penalized, subject to data fit, owing to the simulation‐based assumption that conductivity remains constant or increases over time within the ERI monitoring zone below the water table, and over the monitoring period.…”

Section: Simulation Detailsmentioning

confidence: 99%

“…We use a similar coupling of E4D with a flow and transport simulator to determine the feasibility of contaminant and remedial monitoring at a legacy nuclear waste facility, the Hanford 200 East Area B‐Complex in southeastern Washington State. Previous field hydrogeological and ERI studies have focused on the spatial distribution and transport of contaminants in the vadose zone, specifically nitrates due to the strong conductivity contrast with the native groundwater (Rucker and Fink ; Johnson and Wellman ; Oostrom et al ). No geophysical imaging field studies to date have focused on monitoring contaminant groundwater migration, owing in part to the water table being relatively deep (∼70 m below‐ground surface), which increases the infrastructure and implementation costs associated with ERI monitoring.…”

Section: Introductionmentioning

confidence: 99%

Feasibility Assessment of Long‐Term Electrical Resistivity Monitoring of a Nitrate Plume

2019

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Long‐term monitoring solutions at contaminated sites are necessary to track plume migration and evaluate the performance of remediation efforts. Electrical resistivity imaging (ERI) can potentially provide information about plume dynamics; however, the feasibility and likelihood of success are seldom evaluated before conducting a field study. Coupling flow and transport models with geoelectrical models provide a powerful way to assess the potential effectiveness of an actual ERI field campaign. We present a coupled approach for evaluating the feasibility of monitoring nitrate migration and remediation using 4D time‐lapse ERI at a legacy nuclear waste facility. This kilometer‐scale study focuses on depths below the water table (∼70 m). A flow and transport model is developed to perform simulations of nitrate migration and removal via a hypothetical pump‐and‐treat system. A tracer injection is also simulated at the leading edge of the nitrate plume to enhance the conductivity contrast between the native subsurface and the groundwater fluids. Images of absolute bulk conductivity provide limited information concerning plume migration while time‐lapse difference images, which remove the static effects of geology, provide more useful information concerning plume dynamics over time. A spatial moment analysis performed on flow and transport and ERI models matches well during the tracer injection; however, inversion regularization smoothing otherwise limits the value in terms of locating the center of mass. We find that the addition of a tracer enables ERI to characterize plume dynamics during pump‐and‐treat operations, and late‐time ERI monitoring provides a conservative estimate of nitrate plume boundaries in this synthetic study.

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Interpretation of large‐scale, long‐term electrical geophysical monitoring guided by a process simulation

Robinson,

Johnson,

Thomle

et al. 2024

Vadose Zone Journal

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Surface electrical resistivity tomography (ERT) was used at a waste site to monitor vadose zone changes in electrical properties as a proxy for contaminant flux over a span of 17 years. The BC Cribs and Trenches (BCCT) site at the Hanford site contains 20 disposal trenches and six disposal cribs. Wastes include a large inventory of technetium‐99 and large masses of nitrate and uranium‐238. ERT data were collected along 41 profiles in 2005 to characterize regions of elevated bulk electrical conductivity (BEC) associated with past liquid waste discharges. Previous analyses performed on samples from four boreholes showed a high correlation between nitrate concentration and BEC. In 2022, ERT data were re‐collected along the same profiles and six additional profiles in an area not previously surveyed. Compared to background uncontaminated areas, BEC was higher in contaminated areas at the waste sites. Given the correlation between nitrate concentration and BEC previously found at this site, ERT images show the spatial distribution and relative ionic concentration of vadose zone contaminants at BCCT. Between 2005 and 2022, ERT difference images showed a decrease in BEC surrounding most waste sites, with exceptions where there were known anthropogenic surface changes. An evaluation of recharge‐driven nitrate migration using synthetic flow and transport simulations showed that downward migration causes a decrease in BEC from the decrease in ionic strength at the trailing end of the plume where contaminants migrated downward. From this, we interpret ERT difference images as showing the predominant regions of downward ion flux.

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Deep Vadose Zone Contaminant Flux Evaluation at the Hanford BY-Cribs Site Using Forward and Imposed Concentration Modeling Approaches

Cited by 7 publications

References 28 publications

Groundwater characterization and monitoring at a complex industrial waste site using electrical resistivity imaging

Groundwater characterization and monitoring at a complex industrial waste site using electrical resistivity imaging

Feasibility Assessment of Long‐Term Electrical Resistivity Monitoring of a Nitrate Plume

Interpretation of large‐scale, long‐term electrical geophysical monitoring guided by a process simulation

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