This paper describes an on-going, full-scale anaerobic dechlorination program in Texas, that includes electron donor addition and bioaugmentation of the site groundwater by an ethene-producing D. ethenogenes culture obtained from another project site in New Jersey and acclimated to the Texas project site groundwater. Laboratory-grown bioaugmentation culture is obtained in 20-Liter quantities, and further cultured in an on-site 200-gallon reactor. A portion of this culture is periodically metered into the site groundwater. This project is likely one of the largest full-scale anaerobic dechlorination / bioaugmentation systems in the US. The remedial measures involve extraction of impacted groundwater from a network of 18 extraction wells (14 onsite and 4 off site; 8-acre total area). Electron donors and bioaugmentation water are added to the subsurface via a network of 20 amendment wells located within the source area, as well as near-and faroffsite .
The initial biogeochemical investigation which found several hundred ppm of TCA and PCE in the main source area) showed that biodegradation has occurred at the site, but that electron donor deficiencies are limitingthe complete transformation of PCE and 1,1,1 TCA. Microcosm studies further indicated that dechlorination past cis-dichloroethene was not possible due to the lack of etheneogens at the site, even though vinyl chloride (VC) was detected in the site groundwater at low concentrations (ppb range). The data were interpreted to mean that the VC generation was limited to small localized areas (which were not tested). The site groundwater contains approximately 1,800 ppm of sulfate, which imparts a high electron donor demand to the remedial efforts. Laboratory scale bioaugmentation was successful in acclimating “NJ” D. ethenogenes culture from another project site in New Jersey.
In addition to bioenhncement, the site remediation program includes groundwater extraction (to distribute the bioenhancement amendments),as well as vapor extraction and off-gas treatment using on-site steam-regenerable carbon. The fullscale bioenhancement system has been operating for 4 months and has already improved site conditions by over 70% at some of the site boundary monitoring wells. In one well in particular, MW-38, VC now represents 14.5% of the total chlorinated VOCs in the groundwater, whereas prior to start-up VC was only 0.1% of the total chlorinated VOCs. PCR results for this well are expected to be positive.