title: Impacts of an ethanol-blended fuel release on groundwater and fate of produced methane: Simulation of field observations.
abstract: In a field experiment at Vandenberg Air Force Base (VAFB) designed to mimic the impact of a small-volume release of E10 (10% ethanol and 90% conventional gasoline), two plumes were created by injecting extracted groundwater spiked with benzene, toluene, ando-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. The benzene plume was about 4.5 times longer in the With-Ethanol Lane than in the 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, generally resulted in reasonable yields for microbial growth of 0.01-0.05.
authors.affiliation: Department of Civil and Environmental Engineering, University of California-Davis, One shield Avenue, Davis, California, 95616, USA. erasa@ucdavis.edu.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Rasa
authors.affiliation: U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, California, 94025, USA. babekins@usgs.gov.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Bekins
authors.affiliation: Department of Land, Air, and Water Resources, University of California-Davis, One shield Avenue, Davis, California, 95616, USA. dmmackay@ucdavis.edu.
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Mackay
authors.affiliation: Department of Land, Air, and Water Resources, University of California-Davis, One shield Avenue, Davis, California, 95616, USA. nrdesieyes@ucdavis.edu.
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: de Sieyes
authors.affiliation: U. S. Environmental Protection Agency, Ada, Oklahoma 74820, USA. Wilson.JohnT@epamail.epa.gov.
authors.forename: John T
authors.initials: JT
authors.lastname: Wilson
authors.affiliation: Department of Biology, Boise State University, Boise, Idaho 83725, USA. kevinferis@boisestate.edu.
authors.forename: Kevin P
authors.initials: KP
authors.lastname: Feris
authors.affiliation: CH2M-Hill consultants, 150 Spear Street, Suite 750, San Francisco, CA, 94105, USA. isaac.wood@ch2m.com.
authors.forename: Isaac A
authors.initials: IA
authors.lastname: Wood
authors.affiliation: Department of Land, Air, and Water Resources, University of California-Davis, One shield Avenue, Davis, California, 95616, USA. kmscow@ucdavis.edu.
authors.forename: Kate M
authors.initials: KM
authors.lastname: Scow
keywords: BTEX; Ethanol; anaerobic; methanogenic; reactive transport