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Abstract
ABSTRACT An 8-year bioremediation field study was conducted in a trichloroethene (TCE)-contaminated, highly indurated (i.e., hard), recharge-limited (i.e., contains little water) conglomerate where common remediation strategies, such as groundwater recirculation and direct push installation of a large well network, could not be used. A tracer test using isotopically distinct water from the Hetch Hetchy Reservoir indicated that remediation fluids mainly flowed through fractures and sand lenses in the conglomerate. This was confirmed during in situ bioremediation of the site, in which Dehalococcoides (from a bioaugmentation culture) and volatile fatty acids (from injection of lactate) were the most accurate indicators of transport between wells. Some contaminants were also displaced out of the area due to injection of tracer water. Despite these difficulties, dissolved contaminant mass decreased by an estimated 80% by the end of the test, reaching the lowest values ever recorded at this site. Furthermore, the persistence of ethene 4 years after bioaugmentation suggests that the dechlorinating capacity of the remaining microbial community is comparable to the matrix diffusion of TCE into the dissolved phase.
ACKNOWLEDGMENTS
Robert Devany provided an invaluable technical review of the manuscript. Bill Clark and Kian Atkinson assisted in the field operations associated with this project. Gail Eaton assisted in the isotopic analysis of groundwater samples. The support of Leslie Ferry, Site 300 Project Manager, is greatly appreciated.
FUNDING
This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory Contract DE-AC52-07NA27344.