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Relating subsurface temperature changes to microbial activity at a crude oil-contaminated site

October 13, 2015

Crude oil at a spill site near Bemidji, Minnesota has been undergoing aerobic and anaerobic biodegradation for over 30 years, creating a 150–200 m plume of primary and secondary contaminants. Microbial degradation generates heat that should be measurable under the right conditions. To measure this heat, thermistors were installed in wells in the saturated zone and in water-filled monitoring tubes in the unsaturated zone. In the saturated zone, a thermal groundwater plume originates near the residual oil body with temperatures ranging from 2.9 °C above background near the oil to 1.2 °C down gradient. Temperatures in the unsaturated zone above the oil body were up to 2.7 °C more than background temperatures. Previous work at this site has shown that methane produced from biodegradation of the oil migrates upward and is oxidized in a methanotrophic zone midway between the water table and the surface. Enthalpy calculations and observations demonstrate that the temperature increases primarily result from aerobic methane oxidation in the unsaturated zone above the oil. Methane oxidation rates at the site independently estimated from surface CO2 efflux data are comparable to rates estimated from the observed temperature increases. The results indicate that temperature may be useful as a low-cost measure of activity but care is required to account for the correct heat-generating reactions, other heat sources and the effects of focused recharge.

Citation Information

Publication Year 2015
Title Relating subsurface temperature changes to microbial activity at a crude oil-contaminated site
DOI 10.1016/j.jconhyd.2015.09.007
Authors Ean Warren, Barbara A. Bekins
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Contaminant Hydrology
Index ID 70159008
Record Source USGS Publications Warehouse
USGS Organization National Research Program - Western Branch; Toxic Substances Hydrology Program