A field-scale in situ bioremediation test was conducted at a chlorinated solvent (mainly 1,1,2,2-tetrachloroethane) contaminated aquifer to evaluate the feasibility of source-zone treatment through anaerobic reductive dechlorination. Contaminated groundwater was extracted at the bottom of the testing zone, amended/ mixed with an electron donor (lactate) solution, and reinjected at the head of the testing zone. Both forced groundwater recirculation and lactate injection resulted in significant mobilization of chlorinated contaminants from the source zone, probably through enhanced dissolution of DNAPL (dense nonaqueous phase liquid) pools. The addition of lactate stimulated the establishment of anaerobic conditions in the aquifer and the onset of microbial reductive dechlorination processes. Dechlorination of 1,1,2,2-tetrachloroethane led to the formation of predominantly 1,1,2-trichloroethane and cis-dichloroethene. Noticeably, dechlorination occurred at aqueous 1, 1,2,2-tetrachloroethane concentrations as high as 90 mg L-1, indicating than in situ bioremediation is a feasible source-treatment strategy for chlorinated solvents such as chloroethanes.