Induced-polarization detection and mapping of contaminant plumes

Abstract

Several laboratory and scaled model investigations suggest that organic contaminants affect the surface electrical properties of exposed soils/rocks and therefore produce measurable induced polarization (IP) signatures. However, there is little field evidence of an IP methodology for contaminant mapping. A 2D time-domain IP method is developed for mapping the FS-12 contaminant plume at the Massachusetts Military Reservation (MMR) located in Cape Cod, Massachusetts. The FS-12 plume consists of approximately [Formula: see text] of fuel that erupted from a broken underground pipeline in the early 1970s. Benzene and ethylene dibromide (EDB) are the primary contaminants at FS-12, with concentrations exceeding the allowed maximum concentration levels (MCL), while other constituents of the plume did not exceed their MCL. Therefore, the contaminants of interest are benzene and EDB, partly because of their health risk and partly because they present the highest concentrations (2400 and [Formula: see text], respectively) among the plume constituents and are therefore more likely to be related to the polarization source. IP data were acquired along a survey line that partially transects the plume extending over contaminated and uncontaminated zones and were inverted to give 2D resistivity and chargeability plots to [Formula: see text] depth and a horizontal extent of [Formula: see text]. By separately inverting IP data derived from time windows located at short and long decay times, a time-domain gross (spectral) chargeability difference is produced. Both the chargeability and gross spectral chargeability difference show good agreement with the known location of the plume from monitoring wells, with the IP chargeability section suggesting contaminant distribution detail that cannot otherwise be inferred from the sparse borehole distribution.