Bioaugmentation to Treat Chlorinated Solvents in Fractured Bedrock

ABSTRACT: An in situ bioremediation pilot study was performed at a former industrial site in New Jersey where groundwater has been impacted by historical releases of chlorinated solvents. The target area for treatment is a fractured, intermediate bedrock zone. The remedial objective at the Site is to treat the groundwater while minimizing the impact of the remedial system on the re-development of the Site. Bioaugmentation was selected as the remediation technology to be used in field testing. KB-1™, a natural, non-pathogenic microbial consortium containing several strains of Dehalococcoides ethenogenes, was added to the subsurface to treat chlorinated ethenes. Emulsified soybean oil was used as an electron donor to support reductive dehalogenation of the target compounds. The objectives of the pilot study were to evaluate: (1) the removal of chlorinated volatile organic compounds (CVOCs) as a result of bioaugmentation, and (2) the performance of injection strategies. Two methods of donor addition were performed, (a) passive injection, and (b) an injection followed by temporary groundwater pumping to induce a hydraulic gradient and draw the injected materials through the bedrock fractures.

TCE concentrations in groundwater in the vicinity of the passive injection well decreased from over 800 μ,g/L to 69 μ,g/L, but with limited distribution. At the second injection point, TCE concentrations decreased from 120 μ,g/L to less than 2 μ,g/L in the injection well, and similar results were observed in wells 12 and 24 feet away. In addition, cis-DCE and VC concentrations were also reduced as the contaminants were degraded to ethene and other innocuous compounds. While injection followed by temporary groundwater pumping achieved better distribution, it is likely that the hydraulic conductivity of the formation at the individual injection points had a greater impact on the distribution of injected materials than the injection technique.

Historical releases near a former lamp manufacturing facility in New Jersey (the Site) resulted in elevated concentrations of chlorinated solvents in the subsurface. The volatile organic compounds of concern at the Site are primarily chlorinated ethenes: tetrachloroethene (PCE), trichloroethene (TCE), cis-1,2-dichloroethene (cis-DCE), 1,1- dichloroethene (1,1-DCE), and vinyl chloride (VC). Data collected from a number of wells at the Site indicate that native microorganisms in the subsurface have the ability to degrade the target compounds, primarily TCE, in the intermediate bedrock zone. However, the relatively high concentrations of cis-DCE and VC indicate that reductive dehalogenation was not resulting in the complete mineralization of TCE to ethene and simpler compounds.

A field pilot study was conducted at the Site to evaluate the effectiveness of Enhanced In-Situ Bioremediation (EISB) as a potential site-wide remedy for groundwater and to obtain information to develop a full scale design approach for the Site. As groundwater data collected at the Site indicated that complete reductive dehalogenation was not occurring, both a soluble, food-grade substrate and a microbial culture were added to the subsurface. The culture KB-1™, containing several strains of Dehalococcoides ethenogenes, has been demonstrated to completely degrade tetrachloroethene (PCE) and trichloroethene (TCE). An emulsified oil substrate (EOS®) was used as an electron donor to support the reductive dechlorination of the CVOCs by bacteria contained in the KB-1™ culture.

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