Date of Award

12-2002

Degree Name

Doctor of Philosophy

Department

Geosciences

Abstract

The geoelectric stratigraphy at a site impacted with light non-aqueous phase liquids (LNAPLs) is investigated for its link to natural biodegradation, its contribution to the conductive model for aged (i.e. mature) LNAPL contaminated sites, and the relationship to the natural hydrologic regime. The highest conductivities (lowest resistivities) were observed in portions o f soils where LNAPL was in residual and free phase. Corroborating evidence from bacteria enumeration from soil close to the vertical resistivity probe (VRP) installations show orders-of-magnitude increase in both heterotrophic and oil degrading microbes at the depths where the conductivity was at a maximum. The coincidence o f peak microbial populations with zones of high conductivity provides circumstantial evidence linking the anomalous high conductivity to microbial degradation o f LNAPLs. A simple analysis using Archie's Law reveals that large pore water saturation and a large pore water conductivity enhancement is necessary to produce the VRP field results from the contaminated locations. These results support the conductive model at aged LNAPL contaminated sites due to the effects of enhanced mineral dissolution o f the aquifer materials resulting from biodegradation o f the contaminant mass. Further comparison of the temporal conductivity variation and water table fluctuations are also presented. The VRP results suggest that the conductivity response is inversely related to water table elevations at locations o f LNAPL contamination and directly related at the non-contaminated location. Overall, this study demonstrates the potential o f geoelectrical investigations as a tool for assessing the microbial degradation o f LNAPL impacted soils. The results will guide biogeochemical investigations to discrete zones where, physical changes are occurring, and provide the basis for model calibration at sites with mature LNAPL contamination.

Access Setting

Dissertation-Open Access

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