Sensitivity Analysis of Contaminant Transport from Vadose Zone Sources to Groundwater

Rockhold, Mark; Song, Xuehang; Tagestad, Jerry; Thorne, Paul D.; Tartakovsky, G.

doi:10.2172/1488866

Cited by 2 publications

(4 citation statements)

References 17 publications

(33 reference statements)

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“…Spatial discretization ranges from 0.1 to 2 m in the vertical direction and 4-10 m in the horizontal direction, with finer discretization used in the vicinity of the tanks, the PA, and the fine-grained H2 units. This discretization is finer than what has been used in earlier three-dimensional (3D) models of the site (Rockhold et al 2018a). Neumann-type flux boundaries are applied to the upper surface for the flow equation to represent natural groundwater recharge rates (Fayer and Keller 2007;Last et al 2006).…”

Section: Subsurface Flow and Transport Modelingmentioning

confidence: 99%

“…No-flow conditions were assumed for both water and solutes at the bottom boundary of the domain, which is in basalt. Source terms representing historical releases of liquid waste from tanks, cribs, and trenches were incorporated in the model from published records (Serne et al 2010;Rockhold et al 2018a). Flow and transport modeling were performed for the time period from year 0 to 2045, with years 0 to 1945 representing a period used to establish a steady-state flow field for a pre-Hanford operational setting.…”

Section: Subsurface Flow and Transport Modelingmentioning

confidence: 99%

“…Flow and transport modeling were performed for the time period from year 0 to 2045, with years 0 to 1945 representing a period used to establish a steady-state flow field for a pre-Hanford operational setting. Simulation of liquid waste and disposal of contaminants of concern (e.g., nitrate, Tc-99, uranium) from 1946 to 1972 was based on historical records (Serne et al 2010;Rockhold et al 2018a). Extraction of contaminated groundwater from the PA at the site began in 2011.…”

Section: Subsurface Flow and Transport Modelingmentioning

confidence: 99%

See 2 more Smart Citations

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: Subsurface Flow and Transport Modelingmentioning

confidence: 99%

Section: Subsurface Flow and Transport Modelingmentioning

confidence: 99%

Section: Subsurface Flow and Transport Modelingmentioning

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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“…So far, LSA/GSA has rarely been applied for contaminant transport in the unsaturated zone (Davis et al, 1994;Gatel et al, 2019;Gribb et al, 2002;Pan et al, 2011;Rockhold, 2018;Ciriello et al, 2017), where most studies have considered a homogenous media. Specifically for benzene, few local sensitivity analyses have indicated the degradation and adsorption coefficients as the most important parameters for benzene transport in the unsaturated zone (Gribb et al, 2002;Zanello et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Identification of parameter importance for benzene transport in the unsaturated zone using global sensitivity analysis

Cohen,

Schwartz,

Rosenzweig

2024

Hydrol. Earth Syst. Sci.

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Abstract. One of the greatest threats to groundwater is contamination from fuel derivatives. Benzene, a highly mobile and toxic fuel derivative, can easily reach groundwater from fuel sources and lead to extensive groundwater contamination and drinking water disqualification. Modelling benzene transport in the unsaturated zone can quantify the risk for groundwater contamination and provide needed remediation strategies. Yet, characterization of the problem is often complicated, due to typical soil heterogeneity, numerous unknown site and solute parameters, and the difficulty of distinguishing important from non-important parameters. Thus, sensitivity analysis (SA) methods, such as global SA (GSA), are applied to reduce uncertainty and detect key parameters for groundwater contamination and remediation. Nevertheless, studies devoted to identifying the parameters that determine transport of fuel derivatives in the unsaturated zone are scarce. In this study, we performed GSA to assess benzene transport in the unsaturated zone. First, a simple GSA (Morris) screening method was used for a homogenous sandy vadose zone. Then, a more computationally demanding (Sobol) variance-based GSA was run on the most influential parameters. Finally, the Morris method was tested for a heterogeneous medium containing clay layers. To overcome model crashes during GSA, several methods were tested for imputation of missing data. The GSA results indicate that benzene degradation rate (λk) is the utmost influential parameter controlling benzene mobility, followed by aquifer depth (z). The adsorption coefficient (Kd) and the van Genuchten n parameter of the sandy soil (n1) were also highly influential. The study emphasizes the significance of λk and the presence of clay layers in predicting aquifer contamination. The study also indicates the importance of heterogenous media representation in the GSA. Though identical parameters control the transport in the different soil types, in the presence of both sand and clay, parameters directly affecting the solute concentration like λk and Kd have increased influence in clay, whereas n is more influential for sand comprising most of the profile. Overall, GSA is demonstrated here as an important tool for the analysis of transport models. The results also show that in higher dimensionality models, the radial basis function (RBF) is an efficient surrogate model for missing data imputation.

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Sensitivity Analysis of Contaminant Transport from Vadose Zone Sources to Groundwater

Cited by 2 publications

References 17 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

Identification of parameter importance for benzene transport in the unsaturated zone using global sensitivity analysis

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