Groundwater characterization and monitoring at a complex industrial waste site using electrical resistivity imaging
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PAPER
Groundwater characterization and monitoring at a complex industrial waste site using electrical resistivity imaging M. L. Rockhold 1 & J. L. Robinson 1 & K. Parajuli 1 & X. Song 1 & Z. F. Zhang 1 & T. C. Johnson 1 Received: 28 October 2019 / Accepted: 18 April 2020 # The Author(s) 2020
Abstract 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. Keywords Vadose zone . Contaminant transport . Perched aquifer . Electrical resistivity . USA
Introduction 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). The problem is often worse for sites located in arid and semi-arid regions where the unsaturated zone is relatively thick and the water table is deep (Cassiani
* M. L. Rockhold [email protected] 1
Pacific Northwest National Laboratory, P.O. Box 999, MS K9-36, 902 Battelle Boulevard, Richland, WA 99352, USA
and Binley 2005; Oostrom et al. 2013; Wellman et al. 2013). Characterization of subsurface features a
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