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Evaluation of the Role of Dehalococcoides Organisms in the Natural Attenuation of Chlorinated Ethylenes in Ground Water (121 pp, 2.22 MB)July 2006

At most hazardous waste sites where monitored natural attenuation (MNA) of chlorinated solvents in ground water is successful as a remedy, the chlorinated solvents are biologically degraded to harmless end products such as ethylene or ethane. Many organisms can degrade chlorinated solvents such as tetrachloroethylene or trichloroethylene, to dichloroethylene and vinyl chloride. This contributes little to risk reduction because vinyl chloride is more toxic and more carcinogenic than tetrachloroethylene or trichloroethylene. The only organisms known to degrade dichloroethylenes and vinyl chloride to ethylene or ethane are members of the Dehalococcoides group. As a result, these organisms have a critical role in the evaluation of MNA at chlorinated solvent sites. In recent years, biochemical assays for the presence of DNA from the organisms have become commercially available. These assays are based on the polymerase chain reaction (PCR) for the amplification of DNA extracted from ground water. They are very sensitive and can be very specific.

This report is designed for technical staff in the EPA Regions and in state agencies that require information on the contribution of Dehalococcoides bacteria to MNA of chlorinated solvents, and information on the proper application and interpretation of the assays in an evaluation of MNA. This report includes sections on the role of biotransformation in evaluation of MNA of chlorinated solvents, the ecology of microorganisms that transform chlorinated solvents, tools to assay microorganisms that transform chlorinated solvents, the relationship between Dehalococcoides DNA in ground water and rates of natural attenuation at field scale, the relationship between geochemical parameters and the occurrence of Dehalococcoides DNA in ground water, and the relationship Dehalococcoides DNA in ground water and behavior of chlorinated solvents in laboratory treatability studies or microcosm studies done with water from the plume.


John T. Wilson


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