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Impacts of an ethanol-blended fuel release on groundwater and fate of produced methane: Simulation of field observations
Citation:
Rasa, E., B. Bekins, D. Mackay, N. de Sieyes, J. Wilson, K. Feris, I. Wood, AND K. Scow. Impacts of an ethanol-blended fuel release on groundwater and fate of produced methane: Simulation of field observations. WATER RESOURCES RESEARCH. American Geophysical Union, Washington, DC, 49(8):4907-4926, (2013).
Impact/Purpose:
Submission to Journal of Water Resources Research
Description:
In a field experiment at Vandenberg Air Force Base (VAFB) designed to mimic the impact of a small-volume release of E10, two plumes were created by injecting extracted groundwater spiked with benzene, toluene, and o-xylene, abbreviated BToX (No-Ethanol Lane) and BToX plus ethanol (With-Ethanol Lane) for 283 days. We developed a reactive transport model to understand processes controlling the fate of ethanol and BToX. The model was calibrated to the extensive field dataset and accounted for concentrations of sulfate, iron, acetate, and methane along with iron-reducing Bacteria, sulfate-reducing Bacteria, fermentative Bacteria, and methanogenic Archaea. A number of important processes needed to be incorporated in the model to achieve a match between simulations and the observations. The benzene plume was about 4.5 times longer in the With-Ethanol Lane than No-Ethanol Lane. Matching this different behavior in the two lanes required inhibiting benzene degradation in the presence of ethanol. Inclusion of iron reduction with negligible growth of iron-reducers was required to reproduce the observed constant degradation rate of benzene. Modeling suggested that vertical dispersion and diffusion of sulfate from an adjacent aquitard were important sources of sulfate in the aquifer. Matching of methane data required incorporating initial fermentation of ethanol to acetate, methane loss by outgassing, and methane oxidation coupled to sulfate and iron reduction. Simulation of microbial growth using dual Monod kinetics, and including inhibition by more favorable electron acceptors, resulted in reasonable yields for microbial growth of 0.01-0.05.
