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Wei, Y., N.R. Thomson, R. Aravena, M. Marchesi, J.F. Barker, E.L. Madsen, R. Kolhatkar, et al.
Groundwater Monitoring & Remediation 38(4):73-87(2018)

A surficial infiltration pond overlying a well-characterized shallow aquifer contaminated with petroleum hydrocarbon (PHC) was pilot-tested as a delivery method for sulfate to stimulate PHC bioremediation. The experiment 1) assessed the spatial and temporal distribution of sulfate in groundwater and associated changes in PHC concentrations and 2) augmented conventional groundwater parameters with isotopic and molecular-biological procedures to evaluate enhanced biodegradation of PHCs. A high-resolution monitoring network consisting of multiple transects of depth-discrete sampling points was employed to capture the behavior of the infiltrating sulfate. These data were enhanced with compound-specific isotope analysis (CSIA) and biomarkers. Monitoring data indicated that the sulfate-enriched water mixed with upgradient groundwater as it migrated downward through the residual PHC zone and formed a commingled downgradient plume with the dissolved PHC compounds. The enrichment of δ34S in conjunction with a decrease in sulfate concentration and increased dissolved inorganic carbon concentrations indicated biodegradation of PHCs. Despite fluctuations in benzene, toluene, and o-xylene (BTX) concentrations, CSIA data for BTX showed biodegradation occurred. Biomarker data provided supporting evidence that toluene and o-xylene were undergoing anaerobic biodegradation due to sulfate reduction.

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