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LABORATORY AND FIELD RESULTS LINKING HIGH CONDUCTIVITIES TO THE MICROBIAL DEGRADATION OF PETROLEUM HYDROCARBONS
Citation:
Werkema, D, E. Atekwana, E. A. Atekwana, J. W. Duris, S. Rossbach, J. Allen, L. Smart, AND W. Sauck. LABORATORY AND FIELD RESULTS LINKING HIGH CONDUCTIVITIES TO THE MICROBIAL DEGRADATION OF PETROLEUM HYDROCARBONS. Presented at 2004 Symposium on the Application of Geophysics to Environmental & Engineering Problems, Colorado, Springs, CO, February 22-26, 2004.
Impact/Purpose:
Research is being conducted to improve and evaluate the resolution of the CR, EM, seismic, and GPR methods over complex geological formations (such as fractured geologies) and to evaluate the capability of these geophysical methods to delineate subsurface organic contaminants.
Description:
The results of a field and laboratory investigation of unconsolidated sediments contaminated by petroleum hydrocarbons and undergoing natural biodegradation are presented. Fundamental to geophysical investigations of hydrocarbon impacted sediments is the assessment of how microbial degradational processes affect their geoelectrical response. Therefore, the primary goal of this study was to understand how microbially mediated processes in hydrocarbon impacted sediments influence the geoelectrical response of this impacted zone. The field and laboratory results showed higher bulk conductivity in sediments impacted by petroleum hydrocarbons. The impacted sediments also showed increased populations of alkane degrading microbes and elevated dissolved cations ( e.g. Ca2+). The elevated cations in the contaminated sediments relative to uncontaminated sediments suggest enhanced mineral dissolution related to the microbial degradation of the hydrocarbon. Both the laboratory and field data showed the highest bulk conductivities occurring within zones impacted with the free-phase and residual phase hydrocarbon and not within the water saturated zone. A model using a simplified form of Archie's Law suggests highly elevated estimated pore water conductivities within this conductive zone ( ~4-6 times background bulk conductivity) for both the laboratory and field data. The similar results for hydrocarbon contaminated sediments in laboratory experiments and field settings suggest that the mechanism for the high bulk conductivity in the contaminated zone is related to the microbial metabolism of the hydrocarbon and the resulting geochemical alterations within the contaminated zone. This study demonstrates that the higher bulk conductivity measured by geoelectrical methods at hydrocarbon impacted sites may be in part related to the microbial mineralization of the hydrocarbon.