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CLOSURE REQUEST 5-31-94 <br /> technologies, where large amounts of ground water must be pumped <br /> and treated, vapor extraction produced minor water via <br /> condensation, thus not accelerating the overdraft situation that <br /> is found in the Stockton area water basin. Vapor extraction also <br /> creates an oxygen enhanced environment for the natural <br /> degradation of hydrocarbons and once the VES is terminated <br /> natural oxygen levels will again appear. <br /> VII. REMEDIATION EFFECTIVENESS <br /> a) Are final cleanup levels consistent with the State <br /> Water Resources Control Board Resolution 68-16 <br /> "Statement of Policy with Respect to Maintaining High <br /> Quality of Waters in Califronia"? <br /> MAXIMUM CONTAMINANT LEVELS FOR PRIMARY DRINKING WATER, TITLE 22 <br /> or DHS. <br /> Primary MCL Secondary MCL <br /> (no adverse (aesthetic) <br /> health affects) <br /> BENZENE 1 ug/L <br /> TOLUENE 1000 ug/L 100 ug/L <br /> ETHYLBENZENE 700 ug/L 30 ug/L <br /> Total XYLENES 1750 ug/L 20 ug/L ' <br /> t Vapor extraction has removed most BTEXs from the ground water as <br /> shown by sample results obtained from the monitoring wells . The <br /> primary MCLS have been obtained since September 11, 1992, when <br /> MW1, tested 1. 2 ppb benzene. With this in mind, the "Primary <br /> and Present California Water Quality Goals" have been met for <br /> over 1 year Secondary MCL' s have also been met since September <br /> 15, 1993 , see Table 1 . <br /> b) Verification monitoring program and criteria, <br /> rationale, sampling number, frequency, and duration <br /> As requested by San Jaoquin County Health this site was placed on <br /> a quarterly ground water sampling schedule . Also to confirm the <br /> effects-,. that the VES might have on sample results, the lastest <br /> monitoring was performed with the VES being off for over one <br /> month. As shown on TABLE 1 the Primary MCL' s have been meet and <br /> monitored for over one year. <br /> c) Impact (potential and/or existing) of residual <br /> pollutants on beneficial uses <br /> Utilizing EPA models "VLEACH°' and "BIOPLUME" it was demonstrated y <br /> that no significant impact to ground water exist from the <br /> residual pollutants that remain in the soil at this time . <br /> page25 <br />