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5.0 DISCUSSION AND RECONIIIIENDATIONS <br />' 5 1 Discussion <br /> The following discussion is based on the data collected to date <br /> 1 • Remediation by excavation and disposal of impacted soil was completed in 1987 <br /> Additional site investigation and two years of ground water monitoring have been <br />' conducted at the site during the period of 1990 through 1993 <br /> The additional investigations in the unsaturated soil zone at the site did not find any <br />' potential source areas for hydrocarbons ESE concludes that the overexcavation <br /> performed adequately removed the impacted soil <br />' • Ground water flow beneath the site is generally to the south - southwest with a gentle <br /> gradient and any contaminants present in the ground water will likely migrate this <br /> direction <br />' • TPH-D, and BTEX were not detected in.the ground water samples from any of the wells <br /> during the third and fourth quarter of 1993 <br />' Ground water monitoringat the site has indicated that sporadic, minor "lits" of TPH-D <br /> P <br /> and BTX that have been reported during a single monitoring event have not been verified <br />' in previous or subsequent events (Table 2) Table 3 - Regulatory Threshold Comparison, <br /> compares the maxunum BTEX results to state and federal MCLs and Taste and Odor <br />' Threshold The comparison reveals that of the detectable concentrations of BTX found, <br /> only benzene, found at a concentration of 1 3 µglL in ground water from MW-2 (a cross <br /> gradient well) during one event exceeds the MCL of 1 µglL The occurrence of benzene <br />' in this well has not been verified in four subsequent quarters of monitoring <br />' 5 2 Recommendations <br /> FSE has the following recommendations <br />' • The site should be closed with no further action required based on the lack of evidence <br /> of an onsite source in the unsaturated soil zone and lack of evidence of petroleum <br />' hydrocarbon constituents in ground water above regulatory thresholds <br /> • Upon receiving site closure, the wells should be properly abandoned in accordance with <br />' State of California Well Standards and County of San Joaquin permit requirements <br /> 1 <br />' F 169351MCLOSUPE RPT 11 Environmental Science&Engineering,Inc <br /> 1 <br />