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IN SITU BIOREMEDIATION OF A DNAPL SOURCE AND PLUME: 8 YEARS OF PERFORMANCE DATA
Jacob, C.L. Geological Society of America, Abstracts with Programs 49(6):Paper 69-32(2017)

Full-scale treatment of a TCE source zone and 12-acre plume began in 2005 beneath an active manufacturing building near Portland, Oregon, using food-grade vegetable oil (VO). Contamination occurs within a shallow alluvial aquifer at 10-30 ft, underlain by a competent aquitard. DNAPL was observed, and the maximum baseline TCE concentration in groundwater was 1,170,000 µg/L. Baseline monitoring documented TCE and cDCE predominance in the source and plume, respectively, with low levels of VC and end products ethene and ethane. Effective treatment was achieved at a low cost and with minimal disruption to manufacturing operations using a 2-yr injection frequency. A coarse emulsion of VO and potable water was injected to 18 source wells on 10- to 20-ft centers. About 20,000 gal of 23% VO emulsion was injected during each event. Source zone VO injection resulted in active bioremediation in the source and up to 800 ft downgradient, and in decreased total chlorinated ethene molar mass in the source and throughout the downgradient plume. Increased TOC and methanogenic aquifer redox conditions characterize the active bioremediation zone. Source wells have transitioned from TCE to cDCE predominance with substantial VC and some ethane/ethane also detected. Detection of acetylene in source zone groundwater indicates concurrent abiotic mass destruction. Downgradient wells have transitioned from cDCE to ethane/ethane predominance and total chlorinated ethenes have decreased by 99% throughout the downgradient plume.



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