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Publications > Slater and others, 2010.

Investigation of biogeophysical signatures at a mature crude-oil contaminated site, Bemidji, Minnesota

L.D. Slater (lslater@andromeda.rutgers.edu)
Rutgers-Newark, Newark, NJ, USA

E.A. Atekwana (estella.atekwana@okstate.edu)
Oklahoma State University, Stillwater, OK, USA

A. Revil (arevil@mines.edu)
Colorado School of Mines, Golden, CO, USA

M. Skold (mskold@mines.edu)
Colorado School of Mines, Golden, CO, USA

D. Ntarlagiannis (dimntar@andromeda.rutgers.edu)
Rutgers-Newark, Newark, NJ, USA

Y. Gorby (ygorby@jcvi.org)
Craig Venter Institute, San Diego, CA, USA

F. Mewafy (farag.mewafy@okstate.edu)
Oklahoma State University, Stillwater, OK, USA

F.D. Day-Lewis (daylewis@usgs.gov)
U.S. Geological Survey, Storrs, CT, USA

D.D. Werkema (werkema.d@epa.gov)
U.S. Environmental Protection Agency, Las Vegas, NV, USA

J. Trost (jtrost@usgs.gov)
U.S. Geological Survey MN Water Science Center, Mounds View, MN, USA

G.N. Delin (delin@usgs.gov)
U.S. Geological Survey MN Water Science Center, Denver, CO, USA

W.N. Herkelrath (wnherkel@usgs.gov)
U.S. Geological Survey MN Water Science Center, Menlo Park, CA, USA

Abstract

Recent biogeophysical research suggests that microbial processes and resulting redox conditions at mature, hydrocarbon-contaminated sites undergoing biodegradation generate distinct electrical geophysical signatures. Improved understanding of these geophysical signatures could permit the development of geophysical imaging technologies for long-term, minimally invasive, and sustainable monitoring of natural biodegradation at such sites. The National Crude Oil Spill Fate and Natural Attenuation Research Site, Bemidji, Minnesota, is a unique field laboratory for investigating the geophysical signatures of a mature oil-spill where natural attenuation is well documented at the field-scale. Our attention focused on identifying two proposed source mechanisms for generating biogeophysical signatures: (1) self potential (SP) signals due to current sources (geobatteries) generated at the sharp redox front presented by the water table if/when long-range electron transport between reduced and oxidized zones occurs; and (2) complex resistivity (CR) signals due to enhanced electrochemical storage of charge accompanying microbial growth and biofilm development. We performed SP, CR, and time-domain induced polarization (IP) measurements from the surface, down boreholes, and in the laboratory on cores extracted from the site. Two-dimensional (2D) CR imaging was performed on a transect that intercepted a pool of oil where free product at the water table is ~0.4 m thick (South Pool). Surface SP profiles and 2D IP imaging were conducted on multiple transects, including lines that intercepted the most extensive pool (North Pool) where free product is up to 1 m thick. Self-potential and IP measurements were recorded down a borehole drilled in the North Pool where free product is thickest as well as down a near-identical well at a known uncontaminated site. Surface SP measurements at the North Pool were excessively contaminated by AC power lines that service the facility. However SP measurements at the South Pool, and down boreholes in the North Pool did not exhibit the large (+100 mV) anomalies indicative of a geobattery source current mechanism. It is instead likely that the ~20 mV anomalies observed at this site are driven by electro-diffusion potentials associated with the gradients in the chemical potential of the charge carriers, locally enhanced by reducing conditions driven by biodegradation. Preliminary analysis of the CR measurements conducted on cores extracted from the boreholes show evidence of low frequency polarization enhancement associated with the zone of contamination and the smear zone around the water table.

Final copy as submitted to the American Geophysical Union for publication as: Slater, L., Atekwana, E., Revil, A., Skold, M., Ntartlagiannis, D., Gorby, Y., Mewafy, F., Day-Lewis, F.D., Werkema, D.D., and Trost, J., 2010, Investigation of biogeophysical signatures at a mature crude-oil contaminated site, Bemidji, Minnesota [abs.], in 2010 Fall Meeting, San Francisco, California, 13-17 December 2010, proceedings: American Geophysical Union, Washington, D.C., abstract NS31B-1397.