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IMPACT OF ETHANOL ON THE NATURAL ATTENUATION OF BENZENE, TOLUENE, AND O-XYLENE IN A NORMALLY SULFATE-REDUCING AQUIFER
Citation:
MACKAY, D. M., N. R. DE SIEYES, M. D. EINARSON, K. P. FERIS, A. A. PAPPAS, I. A. WOOD, L. JACOBSON, L. G. JUSTICE, M. N. NOSKE, K. M. SCOW, AND J. T. WILSON. IMPACT OF ETHANOL ON THE NATURAL ATTENUATION OF BENZENE, TOLUENE, AND O-XYLENE IN A NORMALLY SULFATE-REDUCING AQUIFER. ENVIRONMENTAL SCIENCE AND TECHNOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 40(19):6123-6130, (2006).
Impact/Purpose:
To verify conclusions of an experiment.
Description:
Two side-by-side field experiments were conducted in a shallow sulfate-reducing aquifer at a former service station site at Vandenberg Air Force Base, CA. On one side, we injected site groundwater amended with 1-3 mg/L benzene, toluene, and o-xylene (B, T, and o-X). On the other side we injected the same flow rate of groundwater amended with the same concentrations of B, T, o-X, as well as ~500 mg/L ethanol. Comparing the “without ethanol” and “with ethanol” lanes, it is clear that natural attenuation of B, T, and o-X was significantly affected by the presence of ethanol at this site. In the first few months, the B, T, and o-X plumes in both lanes extended approximately the same distance in the direction of flow, but thereafter the plumes in the lane without ethanol retracted significantly and remained retracted for the rest of the experiments. These observations suggest an initial acclimation period, during which the B, T, and o-X plumes grew in length in the lane without ethanol, followed by a rapid improvement in efficiency of natural attenuation under sulfate-reducing conditions. In the lane with ethanol, the B, T, and o-X plumes also retracted, but at a much slower rate and not to as great an extent. Results indicate that the preferential degradation of the ethanol rapidly depleted essentially all of the dissolved sulfate, leading to methanogenic and acetogenic conditions in the vicinity and downgradient of the injection wells. Thus, the B, T, and o-X plumes in the lane with ethanol were migrating along a pathway initially devoid of soluble electron acceptors. The B, T, and o-X in the ethanol-impacted lane were attenuated in part within the methanogenic/acetogenic zone, with rates increasing slowly over a many month time frame, and in part within sulfate-reducing zones developing along the plume fringes due to mixing with sulfate-containing groundwater surrounding the plumes caused by dispersion and/or shifts in flow direction. Overall, this research confirms that ethanol may cause significant impacts on the natural attenuation of aromatic fuel components, in both transient and near steady-state conditions.
