COMPARING THE GEOPHYSICAL SIGNALS BETWEEN THE UNCONTAMINATED AND CONTAMINATED ZONES CONSIDERING THE PRESENCE OF MAGNETITE AT AN OIL SPILL SITE IN BEMIDJI, MINNESOTA

Biogeophysics is a sub-discipline of geophysics that is used to examine how microbial interactions with geologic materials affect the geophysical signatures within the subsurface. At the National Crude Oil Spill Fate and Natural Attenuation Research Site in Bemidji, MN, biogeophysics is being used to study the role of biodegraded hydrocarbons on geophysical signatures. Over time, the microbes are breaking down the hydrocarbons and developing various byproducts via a process called biodegradation. By utilizing geophysical field and laboratory methods, we aim to examine the resistivity and induced polarization response from both a contaminated and an uncontaminated location in Bemidji, MN. This will demonstrate that relatively simple geophysical methods can be used to monitor long term biodegradation of a crude oil spill.

Previous research has shown that geophysical signatures within a contaminant plume where biodegradation has taken place are associated with lower resistivities when compared with areas without contamination. Through the biodegradation process, microbes are consuming the crude oil and are producing biomass, metabolic byproduct and microbial remediated processes which all in turn can increase the electrolytic conductivities of the pore fluid. When the electrolytic conductivities are increased, the resistivities decrease due to the inverse relationship between these two geophysical signatures. Preliminary analysis of 2013 data from the National Crude Oil Spill Fate and Natural Attenuation Research Site in Bemidji, MN is consistent with these findings.