PNNL

Abstract

A contaminated industrial waste site 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 water aquifer (PWA) system using electrical resistivity tomography (ERT). The PWA, 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 PWA 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 were used as the physical basis for ERT modeling. The effectiveness of using surface electrodes, versus surface and horizontal subsurface electrodes, for imaging groundwater extraction from the PWA was investigated. Although directional drilling is a mature technology, electrode emplacement via horizontal wells has not yet been demonstrated. Results from this study indicate that using horizontal subsurface electrodes could significantly improve the ability of ERT to image deep subsurface features and monitor remediation activities in a complex field setting.