Relationship between Dehalococcoides DNA in ground water and rates of reductive dechlorination at field scale

Certain strains of Dehalococcoides bacteria can dechlorinate chlorinated ethylenes to harmless products. This study was conducted to determine if there is a valid association between the density of Dehalococcoides DNA in ground water and the observed rates of reductive dechlorination at field scale. Dehalococcoides DNA in water from monitoring wells was determined using the quantitative real time polymerase chain reaction (q-PCR) with DNA primer set specific for Dehalococcoides organisms. Dechlorination rate constants were extracted from field data using the BIOCHLOR software. Of the six conventional plumes surveyed, “generally useful” rates of dechlorination (greater than or equal to 0.3 per year) of cis-dichloroethylene (cis-DCE) and vinyl chloride (VC) along the flow path were observed at three sites where Dehalococcoides DNA was detected, and little attenuation of cis-DCE and VC occurred at two sites where Dehalococcoides DNA was not detected. At the two sites where there was no net direction of ground water flow, the relationship between the density of Dehalococcoides DNA in ground water and the trend in concentrations of chlorinated ethylenes over time in monitoring wells was not so consistent as that observed for the conventional plumes. A comparison of our study to a field study performed by Lendvay and his coworker indicated that monitoring wells did not efficiently sample the Dehalococcoides organisms in the aquifer.