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.
Highlights
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 objective of the current study is to examine the feasibility of applying electrical resistivity tomography (ERT) for (1) characterization of the spatial extent of a PA underlying a thick vadose zone beneath a large industrial waste disposal complex at the Hanford Site in southeastern Washington State, and (2) monitoring potential remediation efforts associated with subsurface contamination in the deep, variably saturated sediments
While there have been no recent releases of nitrate, slow downward migration of nitrate occurs as a result of simulated natural groundwater recharge, as well as water extraction in the PA
Summary
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 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 and Binley 2005; Oostrom et al 2013; Wellman et al 2013). A perched aquifer is defined as a saturated subsurface region that is above the regional water table, which defines the deep saturated aquifer (Freeze and Cherry 1979). Such perched aquifers (hereafter referred to as PA), may exist as either permanent or temporary features created by a permeable layer overlying a relatively impermeable layer, or in a well-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
