Ground water at Picatinny Arsenal, New Jersey, has been contaminated with chlorinated solvents released from the waste water-treatment system of a metal-plating shop and from overflow from a degreasing vat. Trichloroethylene is the major contaminant, but 1,1,1-trichloroethane and tetrachloroethylene are also present. Cis-1,2-dichloroethylene and vinyl chloride were not original contaminants, but their accumulation in the ground water indicates reductive dechlorination of the trichloroethylene and tetrachloroethylene released to the aquifer. Laboratory microcosms were used to estimate the kinetics of reductive dechlorination at field scale. The microcosms were constructed with aquifer material collected from locations along the longitudinal extent of the plume and from outside the area of contamination. To determine whether supplementary electron donors would enhance reductive dechlorination, three suites of electron donors were added to aquifer material: (1) butyrate, propionate, toluene, and p-cresol; (2) butyrate, propionate, formate, methanol, toluene, and p-cresol; or (3) formate and methanol.