We investigated the bulk electrical conductivity and microbial population distribution in sediments at a site contaminated with light nonaqueous-phase liquid (LNAPL). The bulk conductivity was measured using in-situ vertical resistivity probes; the most probable number method was used to characterize the spatial distribution of aerobic heterotrophic and oil-degrading microbial populations. The purpose of this study was to assess if high conductivity observed at aged LNAPL-impacted sites may be related to microbial degradation of LNAPL. The results show higher bulk conductivity coincident with LNAPL-impacted zones, in contrast to geoelectrical models that predict lower conductivity in such zones. The highest bulk conductivity was observed to be associated with zones impacted by residual and free LNAPL. Data from bacteria enumeration from sediments close to the resistivity probes show that oil-degrading microbes make up a larger percentage (5-55%) of the heterotrophic microbial community at depths coincident with the higher conductivity compared to ∼5% at the uncontaminated location. The coincidence of a higher percentage of oil-degrading microbial populations in zones of higher bulk conductivity suggests that the higher conductivity in these zones may result from increased fluid conductivity related to microbial degradation of LNAPL, consistent with geochemical studies that suggest that intrinsic biodegradation is occurring at the site. The findings from this study point to the fact that biogeochemical processes accompanying biodegradation of contaminants can potentially alter geoelectrical properties of the subsurface impacted media.


Geosciences and Geological and Petroleum Engineering


Petroleum Research Fund
National Science Foundation (U.S.)


Funding of PRF #31594-AC2; NSF DUE-9550974

Keywords and Phrases

Soil Pollution; Biochemistry; Contamination; Electrical Conductivity Measurement; Geochemistry; Microorganisms; Sediments; Bacteria; Biodegradation; Electric Conductivity; Hydrocarbons; Microbiology; Impurities; Population Distribution; Population Statistics; Probes; Biochemistry; Electric Conductivity Measurement; Soil Pollution; Microbial Populations; Spatial Distribution; Apparent Conductivity; Biogeochemical Process; Electrical Conductivity; Geoelectrical Properties; Intrinsic Biodegradation; Light Non-aqueous Phase Liquids; Most Probable Number Methods; Electrical Conductivty Measurements; Geophysical Prospecting; Geophysical Technique; Microorganism; Non-aqueous Phase Liquid; Contaminated Land; Nonaqueous Phase Liquid; Pollution Monitoring; Soil Microorganism; Michigan; North America; United States; Bacteria (microorganisms)

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Article - Journal

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