Initial Site Assessment for Dehalococcoides using PCR and Ethene Concentrations: Comparison with Microcosm Results

Samuel Fogel, Ph.D, Margaret Findlay Ph.D., Donna Smoler (Bioremediation Consulting Inc., Watertown Massachusetts)

The initial evaluation of the bioremediation potential of thirty sites contaminated with chlorinated ethenes and ethanes are being conducted by evaluating the results (for several wells from each site) for three sources of information; (1) the ethene and chloroethane concentration in groundwater samples, (2) the presence of DNA from Dehalococcoides ethenogenes and Dehalobacter by genetic testing using PCR, and (3) microcosm tests with added electron donor, conducted to measure dechlorination of the site contaminants in site groundwater. The sites tested were contaminated by historic releases of industrial chemicals including PCE (tetrachloroethene) and its daughter products, as well as other chlorinated compounds such as 1,1,1-TCA.

Results indicate a strong, but not absolute, correlation between negative PCR results for a well and lack of ethene in the groundwater from that well. For 25 PCR-negative wells from 13 sites, 23 had ethene concentrations less than 0.3 ppb, and 2 had ethene between 6 and 18 ppb. In cases which may arise in which PCR results are positive and microcosm results are negative, it would be concluded that the PCR test is reporting non-viable DNA, indicating that the organisms were previously active, but that changing site conditions have reduced their viability.

For sites having some locations without native dechlorinators, and other locations with native dechlorinators, additional microcosm tests have been useful in designing strategies for intra-site bioaugmentation. For those sites having all wells negative for both microcosm and PCR, additional detailed microcosm tests have been employed to design the strategy for site modification and bioaugmentation with laboratory-grown dechlorinating cultures.