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Using Geophysical Signatures to Investigate Temporal Changes Due to Source Reduction in the Subsurface Contaminated with Hydrocarbons
Citation:
Vukengkeng, C., E. A. Atewanta, E. A. Atekwana, W. A. Sauck, S. Rossbach, J. Nolan, AND D. D. WERKEMA. Using Geophysical Signatures to Investigate Temporal Changes Due to Source Reduction in the Subsurface Contaminated with Hydrocarbons. Presented at AGU Chapman Conference on Biogeophysics, Portland, MA, October 13 - 16, 2008.
Impact/Purpose:
Presentation
Description:
We investigated the geophysical response to subsurface hydrocarbon contamination source removal. Source removal by natural attenuation or by engineered bioremediation is expected to change the biological, chemical, and physical environment associated with the contaminated matrix. Our objective was to determine the effects of contaminant reduction on the contaminant plume as observed by anomalously high bulk electrical conductivity. We compared ground penetrating radar, self potential, and electrical resistivity surveys conducted between 1996 and 2007. In addition, we used groundwater chemistry as part of our evaluation of temporal changes in the chemical conditions in the groundwater. Removal of the contaminant source by soil vapor extraction (SVE) in 2001 caused a decrease in the total petroleum hydrocarbon in groundwater. Geophysical surveys across the contaminated plume showed that attenuated ground penetrating radar reflections became less attenuated, self potential signals became less positive, and electrical resistivity increased over time. We attribute the change in the geophysical properties mainly to removal of hydrocarbon in the free phase. We infer that as long as the free phase contamination does not contribute to microbial degradation, the bulk electrical properties of the subsurface will revert to background conditions. Therefore we conclude that the contaminant mass reduction in the subsurface by natural bioremediation or enhanced remediation can be effectively imaged by integrated geophysical techniques.