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A Tracer Test to Characterize Treatment of TCE in a Permeable Reactive Barrier
Citation:
SHEN, H., J. T. WILSON, AND X. LU. A Tracer Test to Characterize Treatment of TCE in a Permeable Reactive Barrier. GROUNDWATER MONITORING AND REMEDIATION. National Ground Water Association, Westerville, OH, 32(4):32-41, (2012).
Impact/Purpose:
Journal article for Ground Water Monitoring & Remediation
Description:
A tracer test was conducted to characterize the flow of ground water surrounding a permeable reactive barrier constructed with plant mulch (a biowall) at the OU-1 site on Altus Air Force Base, Oklahoma. This biowall is intended to intercept and treat ground water contaminated by trichloroethylene (TCE) in a shallow aquifer. The biowall is 139-meter (m) long, 7.3-m deep and 0.5-m wide. Bromide was injected from an upgradient well into the ground water as a conservative tracer, and was subsequently observed breaking through in monitoring wells within and downgradient of the biowall. The bromide breakthrough data demonstrate that ground water entering the biowall migrated across it, following the slope of the local ground-water surface. The average seepage velocity of ground water was approximately 0.06 m per day. Based on the Darcy velocity of ground water and geometry of the biowall, the average residence time of ground water in the biowall was estimated at 10 days. Assuming all TCE removal occurred in the biowall, the reduction in TCE concentrations in ground water across the biowall corresponds to a first-order rate constant in the range of 0.38 to 0.15 per day. As an independent estimate of the rate constant, STANMOD software was used to fit curves through data on the breakthrough of bromide and TCE in selected wells down gradient of the injection wells. Best fits to the data required a first order rate constant for TCE removal in the range of 0.13 to 0.17 per day. The approach used in this study provides an objective evaluation of the remedial performance of the biowall that can provide a basis for design of other biowalls that are intended to remediate TCE-contaminated ground water.
