Field demonstration of in situ vitamin B12-catalyzed reductive dechlorination

Groundwater at Graces Quarters, Aberdeen Proving Ground (APG), Maryland, is contaminated with a complex mixture of chlorinated methanes, ethanes, and ethenes. The total concentration of chlorinated aliphatic hydrocarbons (CAHs) in the source area groundwater monitoring wells ranges from 4,000 to 6,000 micrograms per liter(mug/L). Based on promising laboratory-scale treatability test results, a 6-month field demonstration was conducted in 1999/2000 to evaluate using reduced vitamin B-12 to abiotically dechlorinate the contaminants, followed by biological degradation of the daughter products. Contaminated groundwater from the site was mixed in situ with the vitamin B-12 concentrate using a groundwater recirculation well as an in situ chemical reactor. Remedial effectiveness was evaluated through a comprehensive groundwater sampling and analysis program using a network of multiple-depth piezometers and monitoring wells in the area. The results show that the chlorinated methanes were rapidly degraded with slower degradation of the chlorinated ethanes. The chlorinated ethenes formed as daughter products are undergoing biological degradation.