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6.0 CONCLUSIONS AND RECOMMENDATIONS This study was successful in determining that no detectable amount of TCE is i present in groundwater at locations sampled. Despite the presence of petroleum hydrocarbons . ' present in shallow groundwater, low detection limits for VOCs were achieved in the laboratory. Benzene and cis-1,2-dichloroethene were detected at levels just above their respective reporting ® limits. This is consistent with previous studies, which found no VOCs (with high detection limits)and high concentrations of total petroleum hydrocarbons. Although TCE was detected in the soil during a previous investigation (Geological Technics, 1996),TCE has not migrated into groundwater. Cis-1,2-Dichloroethene was detected in one shallow groundwater sample. The presence of this compound may indicate that TCE in the subsurface is undergoing biodegradation. Alone chlorinated solvents biodegrade slowly; however, in the presence of a carbon source such as petroleum hydrocarbons,TCE is known to be dechlorinated by microorganisms. The most common intermediate breakdown product of TCE is cis-1,2-dichloroethene (Wiedemeier et al., 1996). i Although previous studies indicate TCE is present in the soil, it has not migrated to groundwater at detectable concentrations. In addition, there is evidence that TCE at this site is undergoing biodegradation. Data collected during this investigation do not indicate that TCE and other chlorinated hydrocarbons have migrated into the groundwater from releases from the condensate outlet pipe. Cis-1,2-Dichloroethene was the only chlorinated hydrocarbon detected in the groundwater samples; its concentration was less than its maximum contaminant level (MCL). The presence of cis-1,2-Dichloroethene indicates that biodegradation of TCE and chlorinated hydrocarbons is probably occurring in the subsurface at the site. It is probable that TCE concentrations in soil will decrease with time, 35275 Welty Road,Vernalis 16 March 1997