POST REMEDIATION CHARACTERIZATION OF LNAPL USING DIRECT PUSH ELECTRICAL RESISTIVITY TOMOGRAPHY

Site characterization of LNAPL plumes continues even after a contaminated site has undergone remediation, since a site must be determined to pose no significant risk to be closed in most states. The standard method is to monitor wells over a period of time and interpret whether a site has been effectively remediated. If the level of LNAPL is still above acceptable levels, the site characterization is often determined to be incomplete due to either a poorly understood geological framework or an unknown source. A study was performed to test the effectiveness of a direct push electrical resistivity tomography (DPERT), in evaluating post remediation LNAPL traces. The site used for the study had previously undergone separate pump-and-treat and surfactant flush remediation. The study utilized direct push techniques to install vertical electrodes at approximately 24 feet in depth. The vertical electrodes were sampled in conjunction with surface electrodes to generate an electrical tomogram of the subsurface electrical properties. The tomograms were correlated with core samples, direct push electrical conductivity logs and chemical analyses. The technique illustrated several locations of remaining LNAPL at the site that existed away from monitoring well locations.