Aromatic and chlorinated hydrocarbons are hazardous organics which persist in groundwater impacted by landfill leachate. Recent studies have indicated that the aromatics biodegrade readily under aerobic conditions. Similarly, methane-oxidizers are reported to metabolize trichloroethylene. This study investigates an in-situ biorestoration scheme involving stimulating aerobic biodegradation in a contaminated anaerobic, methane-saturated groundwater using hydrogen peroxide as an oxygen source. Batch biodegradation experiments were conducted with groundwater and core obtained from the Gloucester Landfill, Ottawa, Canada. Hydrogen peroxide, added at a non-toxic level, provided oxygen which promoted the rapid biodegradation of benzene, toluene, ethyl benzene, o-, m-, and p-xylene. Morphologically different methane-oxidizing cultures were obtained from Gloucester groundwater and a surface sediment. Both cultures degraded trichloroethylene in microcosms containing a mineral media and Gloucester core. Degradation was not observed when the mineral madia was replaced with Gloucester groundwater, or when other chlorinated hydrocarbons were added. Additional research is required to identify and overcome this inhibition to trichloroethylene biodegradation, before this remedial strategy can be employed.