The technical objective of this research was to test whether above-ground, fixed-film bioreactors can biodegrade complex mixtures of chlorinated aromatic compounds in groundwater. Specifically, the project was designed to test the metabolic capabilities of Pseudomonas Strain JS150 in the field. The approach involved a preliminary field study at Robins AFB GA using two above-ground, fixed-film bioreactors, one colonized with Pseudomonas JS150 and one colonized with indigenous groundwater bacteria, to measure degradation of chlorinated aromatic compounds. Independent variables measured included temperature, pH, dissolved oxygen, and fluctuations in microbial populations. Results from the bench-scale column study indicated that the JS150 isolate had the greatest number of desirable qualities and would be the best selection to utilize in a biofilm reactor. Results from the study indicate that both reactors provided substantial chlorobenzene removal (greater than 95%). Data indicate that bioreactor inoculation may be useful for reducing startup time. No degradation intermediates were detected from either the inoculated or uninoculated reactors.