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contained detectable levels of benzene or MTBE The extent of contaminants in ground water to <br /> the northwest of the site has been delineated by Well MW-7 <br /> In general, it appears that petroleum hydrocarbons are present primarily in the vicinity of the <br /> former USTs and the southwest corner of the site Off-site migration of petroleum hydrocarbons to <br /> ground water has been minimal <br /> Deep Monitoring Wells <br /> Two deep ground water monitoring wells were installed on-site to evaluate vertical migration of <br /> contaminants into the deeper water bearing zone Ground water samples collected from MW-12 and <br /> MW-13 did not contain detectable levels of TPPH, benzene or MTBE Well MW-12 contained <br /> ethanol at a concentration of 38,000 ppb This appears to be an anomalous finding as none of the <br /> other wells on-site have contained detectable concentrations of ethanol <br /> Xylenes were detected in Well MW-13 at a concentration of 2 6 ppb, which is also an anomalous <br /> finding Although this is a very low concentration of xylene, and is more than 600 times below the <br /> State of California Maximum Contaminant Limit for drinking water, it is atypical for a petroleum <br /> hydrocarbon release Typically, MTBE or benzene are the first compounds to be detected as these <br /> two compounds tend to be at the leading edge of the plume Further monitoring of these two wells <br /> will be performed to evaluate the validity of these findings <br /> TPPH, benzene and oxygenate compounds were not detected in Well MW-14, located at 2452 <br /> Country Club Boulevard Xylenes were detected in this well at 0 63 ppb, slightly over the detection <br /> limit for this compound As with Well MW-13, this is an atypical occurrence of xylenes, which are <br /> not typically found in a well without benzene and/or MTBE appearing first Additional monitoring <br /> of this well will be performed to determine the validity of this finding <br /> The Caltrans Irrigation Well <br /> Ground water samples collected from the Caltrans well on two different sampling events have <br /> contained concentrations of toluene, but no detectable levels of benzene, MTBE, or other <br /> oxygenates Ground water samples from the first sampling event on September 5, 1997 contained <br /> 280 ppb TPPH and 160 ppb toluene Ground water samples from this event were also analyzed for <br /> VOCs and found to contain only toluene Ground water samples from the second sampling event <br /> performed on December 2, 1997 did not contain detectable levels of TPPH, and only 1 0 ppb <br /> toluene <br /> 240-0783 18 <br />