A simple batch microcosm had previously been developed to simulate the behavior of volatile organic compounds in unconsolidated subsurface material. The microcosm was evaluated by comparing the behavior of tetrachloroethylene, bromoform, carbon tetrachloride, 1,2-dichlorobenzene, and hexachloroethane in (1) the microcosm, (2) the microcosm constructed with autoclaved material, and (3) an experimental plume constructed in a joint field study conducted by Stanford University and the University of Waterloo at a site on Canadian Forces Base, Borden, Ontario. The microcosm study adequately simulated nonbiological removal of these compounds from solution in the experimental plume. However, it failed to detect biotransformation of 1,2-dichlorobenzene despite extensive degradation of this compound in the field. One of the samples of aquifer material used to construct the microcosms had a much greater capacity to biotransform bromoform and carbon tetrachloride than did the other samples of aquifer material, or the aquifer in general. As a result, the microcosm study overestimated biotransformation of bromoform and carbon tetrachloride. The microcosm accurately simulated the behavior of tetrachloroethylene and hexachloroethane.