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WATER RESOURCES RESEARCH,
VOL. 41,
W02001,
doi:10.1029/2004WR003433,
2005
Use of dissolved and vapor-phase gases to investigate methanogenic degradation of petroleum hydrocarbon contamination in the
subsurface
Richard T. Amos
Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada
K. Ulrich Mayer
Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada
Barbara A. Bekins
U.S. Geological Survey, Menlo Park, California, USA
Geoffrey N. Delin
U.S. Geological Survey, Mounds View, Minnesota, USA
Randi L. Williams
Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada
Abstract
At many sites contaminated with petroleum hydrocarbons, methanogenesis is a significant degradation pathway. Techniques to
estimate CH4 production, consumption, and transport processes are needed to understand the geochemical system, provide a complete carbon
mass balance, and quantify the hydrocarbon degradation rate. Dissolved and vapor-phase gas data collected at a petroleum hydrocarbon
contaminated site near Bemidji, Minnesota, demonstrate that naturally occurring nonreactive or relatively inert gases such
as Ar and N2 can be effectively used to better understand and quantify physical and chemical processes related to methanogenic activity
in the subsurface. In the vadose zone, regions of Ar and N2 depletion and enrichment are indicative of methanogenic and methanotrophic zones, and concentration gradients between the
regions suggest that reaction-induced advection can be an important gas transport process. In the saturated zone, dissolved
Ar and N2 concentrations are used to quantify degassing driven by methanogenesis and also suggest that attenuation of methane along
the flow path, into the downgradient aquifer, is largely controlled by physical processes. Slight but discernable preferential
depletion of N2 over Ar, in both the saturated and unsaturated zones near the free-phase oil, suggests reactivity of N2 and is consistent with other evidence indicating that nitrogen fixation by microbial activity is taking place at this site.
Received 20
June
2004;
accepted 3
November
2004;
published 2
February
2005.
Keywords: gas advection;
methanogenesis;
nonreactive gases;
petroleum hydrocarbons.
Index Terms: 0432 Biogeosciences: Contaminant and organic biogeochemistry (0792); 1829 Hydrology: Groundwater hydrology; 1831 Hydrology: Groundwater quality; 1832 Hydrology: Groundwater transport; 1875 Hydrology: Vadose zone.
Read Full Article (file size: 749540 bytes) Cited by
Citation: Amos, R. T., K. U. Mayer, B. A. Bekins, G. N. Delin, and R. L. Williams
(2005),
Use of dissolved and vapor-phase gases to investigate methanogenic degradation of petroleum hydrocarbon contamination in the
subsurface,
Water Resour. Res.,
41,
W02001,
doi:10.1029/2004WR003433.
Copyright 2005 by the American Geophysical Union.
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