--> --> Abstract: Natural Attenuation of Petroleum Hydrocarbons in a Prolific Outwash Sand and Gravel Aquifer, by J. A. Mundell, J. A. Berndt, and J. Arnold; #90926 (1999)

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MUNDELL, JOHN A., and JAMES A. BERNDT, Mundell & Associates, Indianapolis, IN; and JOSEPH ARNOLD, Indianapolis Department of Public Works, Indianapolis, IN

Abstract: Natural Attenuation of Petroleum Hydrocarbons in a Prolific Outwash Sand and Gravel Aquifer

The Indianapolis Department of Transportation's West Street Maintenance Facility is located within 400 ft of the White River near downtown Indianapolis. Beneath the facility, extensive sand and gravel outwash deposits are present which allow rapid groundwater movement and subsequent discharge to the River. Detection of a release of petroleum hydrocarbons from five underground storage tanks in 1990 prompted a multiphase investigation of the release and documentation of the full extent of the groundwater plume with a comprehensive monitoring well network. Since the detection of the release, eight years of groundwater monitoring data have shown the extent of the plume has stabilized and never reached the river despite significant groundwater velocities. In addition, plume concentrations of benzene, toluene, ethylbenzene and xylene have decreased over time without active remediation occurring other than the initial storage tank and associated soil removal, and limited free-product removal from monitoring well bailing activity. As part of a Corrective Action Plan (CAP) submittal to the Indiana Department of Environmental Management, a comprehensive area groundwater flow model coupled with two-dimensional chemical transport modeling were used to evaluate chemical degradation rates and to predict the expected concentration declines as a result of the original source removal and biodegradation. The modeling results suggested that an additional 2 to 3 years of monitoring data would confirm that natural attenuation was stabilizing and reducing the plume size. This evaluation supported a "no action/monitoring only" corrective action plan that continues to document the effectiveness of natural attenuation as the remediation alternative of choice.

AAPG Search and Discovery Article #90926©1999 AAPG Eastern Section Meeting, Indianapolis, Indiana