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k%j KLEINFELRER <br /> To assess the ground water status, Kleinfelder collected quarterly ground water samples <br /> from the eight onsite monitoring wells and submitted them for analysis of total petroleum <br /> hydrocarbons,benzene, toluene, ethylbenzene and xylene. Prior to operation of the vapor <br /> extraction system, benzene was detected in the ground water at concentrations up to 230 <br /> ug/I, toluene at concentrations up to 130 ug/l, ethylbenzene at concentrations up to 15 <br /> ug/l, and xylenes at concentrations up to 1600 ug/1. Total petroleum hydrocarbons were <br /> reported at concentrations up to 1.8 mg/l. After operation of the vapor extraction system, <br /> hydrocarbon concentrations in the ground water appear substantially reduced. Except for <br /> 1.3 ug/l toluene detected in a sample from MW-2,no benzene,toluene, ethylbenzene, or <br /> xylene were detected in the last quarterly sampling round. Low concentrations (less than 1 <br /> mg/1)of an unidentified hydrocarbon mixture were reported in samples from wells located <br /> hydraulically upgradirnt,downgradient,and laterally of the tank excavation. The origin of <br /> this hydrocarbon is unknown. The hydrocarbon could be weathered gasoline, gasoline <br /> constituents, or some other hydrocarbon. The detected concentrations, reported as total <br /> petroleum hydrocarbons,are low and do not appear to be of concern. <br /> Based on the apparent reduction of hydrocarbons and absence of detectable benzene, <br /> toluene,ethylbenzene,and xylene,in the soil aad ground water,the vapor extraction system <br /> appears to have significantly reduced the contaminant concentrations in the vadose zone <br /> and ground water. Therefore, Kleinfelder recommends dismantling the vapor extraction <br /> system and abandoning the eight monitoring wells located at the site. <br /> 113-88-908 . 2 <br />