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Environmental Health - Toxic Substances


U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

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Use of Carbon and Hydrogen Stable Isotopes to Investigate the Production and Fate of Methane at a Toxic Waste Site, Bemidji, Minnesota


Kinga Revesz (U.S. Geological Survey, 431 National Center, Reston, VA 22092), Tyler Coplen (U.S. Geological Survey, 431 National Center, Reston, VA 22092), Mary J. Baedecker (U.S. Geological Survey, 431 National Center, Reston, VA 22092), and Marc Hult (U.S. Geological Survey, 2280 Woodale Drive, Mounds View, MN 55112)


Stable carbon and hydrogen isotope ratios of dissolved methane and aqueous carbon dioxide in the saturated zone of a crude oil spill near Bemidji, Minn., support the concept of methane production by acetate fermentation with concomitant increase in bicarbonate concentration as opposed to carbon dioxide reduction (and bicarbonate consumption). Oxidation of dissolved methane along the lateral flow path seems to be minimal because no measurable change in isotopic composition of methane occurs with distance from the oil body. As methane from the ground water diffuses upward through a 5- to 7-meter-thick unsaturated zone, it is partially oxidized to carbon dioxide, increasing the delta13C of the remaining methane, decreasing the delta13C of the carbon dioxide, and increasing the pressure of carbon dioxide in the unsaturated zone.

No increase of concentrations of atmospheric methane was detected at ground level directly above the oil >plume; concentrations were identical to those of a background atmospheric sample.

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