A pilot test for in situ vitamin B_(12)-catalyzed reductive dechlorination of chlorinated solvents was conducted for 14 weeks in 1999 at Graces Quarters, Aberdeen Proving Ground, Maryland. Groundwater at the site is contaminated with 1,1,2,2-tetrachloroethane (TeCA), carbon tetrachloride (CT), trichloroethene (TCE), tetrachloroethene (PCE), and chloroform (CF). Although analytical groundwater data from the pilot test showed favorable results, biological fouling of the chemical injection/recirculation well and the near-by formation halted pilot test operations. After successful redevelopment of the injection/recirculation well, and several modifications to the chemical treatment mix and injection strategy (aimed at preventing future biofouling) the pilot test was resumed. Modifications included the use of a non-oxidizing biocide, Tolcide~R, containing tetrakis(hydroxymethyl)phosphonium sulfate (THPS) as the active ingredient. The data show that daily application of Tolcide~R at a 150 mg/L active concentration for 4 hours prevented biological fouling of the area surrounding the well. The inhibitory effects of Tolcide~R were limited to the anaerobic treatment zone. Microbial activity was resumed in the aquifer as Tolcide~R concentrations decreased. A laboratory microcosm study confirmed the inhibitory effects of Tolcide~R on the site bacteria.
展开▼
