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IMPACT OF COSOLVENT FLUSHING ON SUBSURFACE MICROBIAL ECOLOGY AT THE FORMER SAGE'S DRY CLEANER SITE
Citation:
Mravik*, S C., A L. Wood*, H. Shen, R. K. Sillan, AND G. W. Sewell. IMPACT OF COSOLVENT FLUSHING ON SUBSURFACE MICROBIAL ECOLOGY AT THE FORMER SAGE'S DRY CLEANER SITE. Presented at 4th Int'l. Conf. Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 24 - 27, 2004.
Impact/Purpose:
To inform the public.
Description:
The Solvent Extraction Residual Biotreatment (SERB) technology was evaluated at the former Sage's Dry Cleaner site in Jacksonville, FL where an area of tetrachloroethylene (PCE) contamination was identified. The SERB technology is a treatment train approach to complete site restoration, which combines an active in situ dense nonaqueous phase liquid (DNAPL) removal technology, cosolvent extraction, with a passive enhanced in situ bioremediation technology, reductive dechlorination. During the in situ cosolvent extraction test approximately 34 kL of 95% ethanol/5% water (v:v) were flushed through the contaminated zone which removed approximately 60% of the estimated PCE mass. Approximately 2.72 kL of ethanol were left in the subsurface, which provided electron donor for enhancement of biological processes in the source zone and down-gradient areas. Results from ground water monitoring indicate reductive dechlorination transformations of tetrachloroethylene have been enhanced following the introduction of ethanol to the system.
Subsurface samples were collected from several locations prior to and following the cosolvent extraction demonstration to evaluate changes in total biomass and microbial population through phospholipid fatty acid (PLFA) analysis. Total biomass estimates were fairly low in most of the samples, with the majority of samples containing biomarkers representative for gram negative bacteria. When normalized to background samples, total and gram negative biomass was significantly higher (95% C.L.) in the one-year and two-year post-cosolvent flushing samples compared to the pre-treatment samples. PLFA data and comparisons to electron donor/electron acceptor concentrations will be presented. Polymerase chain reaction (PCR) results from ground water collected from the source zone three years following the cosolvent flush were positive for the presence of Dehalococcoides, which are the only organisms shown to completely dechlorinate tetrachloroethylene to ethene.