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COMPARISON OF PCR, MICROCOSMS, AND ETHENE FOR INITIAL SITE EVALUATION

Margaret.Findlay Ph.D., Samuel Fogel Ph.D., Donna Smoler, Scott Douglas,(Bioremediation Consulting Inc).
S.Fam, (Innovative Engineering Solutions Inc.), Anthony Pirelli, George Sylvester, Michael Gaudette (Univar, USA)

The initial evaluation of the remediation potential of twenty 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 concentration in groundwater samples, (2) the presence of DNA from D.ethenogenes 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 1,1,1-TCA (trichloroethane) and their daughter products, as well as chlorinated methanes and benzenes.

Results for the first several sites 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. 

For sites for which the microcosm tests are complete, eight PCR-negative wells have tested microcosm-negative, and three have tested microcosm-positive. 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. 

Complete data on at least 20 sites is expected to be compiled within 6 months.

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