Field-Scale Evaluation of Bioaugmentation Dosage for Treating Chlorinated Ethenes

A field demonstration was performed to evaluate the impacts of bioaugmentation dosage for treatment of chlorinated ethenes in a sandy-to-silty shallow aquifer. Specifically, bioaugmentation using a commercially available Dehalococcoides (DHC)-containing culture was performed in three separate groundwater recirculation loops, with one loop bioaugmented with 3.9 x 10¹¹ DHC, the second loop bioaugmented with 3.9 x 10¹² DHC, and the third loop bioaugmented with 3.9 x 10¹³ DHC. Groundwater monitoring was performed to evaluate DHC growth and migration, dechlorination rates, and aquifer geochemistry. The loop inoculated with 3.9 x 10¹² DHC showed slower dechlorination rates and DHC migration/growth compared with the other loops. This relatively poor performance was attributed to low pH conditions. Results for the loops inoculated with 3.9 x 10¹¹ and 3.9 x 10¹³ DHC showed similar timeframes for dechlorination, as evaluated at a monitoring well approximately 10 feet downgradient of the DHC injection well. Application of a recently developed one-dimensional bioaugmentation fate and transport screening model provided a reasonable prediction of the data in these two loops. Overall, these results suggest that increasing bioaugmentation dosage does not necessarily result in decreased dechlorination timeframes in the field. The ability to predict results suggests that modeling potentially can serve as an effective tool for determining bioaugmentation dosage and predicting overall remedial timeframes.