Investigating the geoelectrical response of hydrocarbon contamination undergoing biodegradation

A newly proposed geoelectrical model for hydrocarbon contaminated sites predicts high conductivities coincident with the contaminated zone as opposed to the traditionally accepted low conductivity. The model attributes the high conductivities to mineral weathering resulting from byproducts of microbial redox processes. To evaluate this conductive model, in situ vertical conductivity measurements were acquired from a light non-aqueous phase liquid (LNAPL) contaminated site. The results showed high conductivities coincident with the zone of contamination and within the smear zone influenced by seasonal water table fluctuations. We infer this zone as an active zone of biodegradation and suggest significant microbial degradation under partially water saturated conditions. A simple Archie's Law analysis shows large pore water conductivities necessary to reproduce the bulk conductivity measured at the contaminated location. This study supports the conductive layer model and demonstrates the potential of geoelectrical investigations for assessing microbial degradation of LNAPL impacted soils.