Bioaugmentation and Biostimulation to Remediate Contaminated Ground Water
Silicon Valley, California
Ground water at an industrial site in California has been affected by unintended releases of chlorinated and aromatic volatile organic compounds (VOCs). Contaminants consist primarily of trichloroethene (TCE), degradation products cis-1,2-dichloroethene (cis-1,2-DCE), and vinyl chloride, as well as ethylbenzene, xylenes, and toluene. Weiss Associates conducted a feasibility study and concluded that in-situ bioremediation and bioaugmentation would hasten progress towards cleanup of the site. The remediation work was conducted in two phases where emulsified soybean oil was injected as an electron donor to reductively dechlorinate VOCs. The concentrated oil-in-water emulsion was diluted to approximately 2 percent oil by volume with ground water extracted from the Site. During Phase I of the project, approximately 26,000 gallons of 2 percent emulsified oil were simultaneously injected through nine temporary injection wells. During Phase II of the project, a total of forty temporary injection points were installed and approximately 91,000 gallons of 2 percent emulsified oil were injected into the subsurface. To reduce the likelihood of partial dechlorination and increase the rate of reductive dechlorination, 20 injection points were also bioaugmented with Dehalococcoides ethenogenes culture KB-1.
Performance monitoring indicated a rapid decrease in TCE concentrations. Sampling after six and nine months indicated that TCE in many wells was near or below the analytical reporting limits and more than 99 percent of the TCE had been converted to cis-1,2-DCE, vinyl chloride and ethene. Polymerase chain reaction analysis of ground water samples collected after three months confirmed the presence of dechlorinating organism Dehalococcoides ethenogenes 30 feet downgradient of the injection zone.
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