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IMPORTANCE OF UNUSUAL DICHLOROETHYLENE ISOMER RATIOS AND SEWER LEAKAGE TO AN IN SITU REMEDIATION
Studer, J.E.
CleanUp 2017: Proceedings, 7th International Contaminated Site Remediation Conference, 10-14 September, Melbourne, Australia. p 261-262, 2017

Outcomes from a field pilot test of Biogeochemical Reductive Dechlorination (BiRD) for in situ groundwater treatment strayed significantly from general expectations. The subject site is located in a congested urban area on the Gulf Coast of Florida, overlying a freshwater chlorinated VOCs plume that affects 1.5 hectares of variably weathered limestone bedrock to a depth of over 40 m below grade. The goal was to reduce, at the lowest practical cost, the summed groundwater concentration of TCE and the transformation product isomers of DCE plus VC from ~5,000 µg/L to < 90 µg/L. Subsequent careful review of pilot performance data and insights obtained from a bench-scale study led to identification of previously unsuspected features that would have indicated the incompatibility of the technology with the remedial goal. First, natural biotransformation of TCE to DCE isomers occurs with the documented groundwater concentration ratio of trans-1,2 DCE to cis-1,2 DCE often exceeding 1 and occasionally approaching 4.5. These values deviated significantly from the typical value of ~0.1 and suggest the presence of special partial dechlorinators. Second, unsuspected sewer leakage introduced nitrogen to the alluvium, resulting in maximum detected NO3 of 120 mg/L in shallow bedrock. Following discovery and repair of the sewer break, in-depth analysis aided by bench study insights suggested that BiRD can be a good match for the bedrock if an improved reagent distribution process is implemented. http://www.cleanupconference.com/wp-content/uploads/2017/09/CleanUp_2017_Proceedings_Low-Res.pdf



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