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} CRYSTAL CREAMERY STOCKTON <br /> WKA No. 1628.10 <br /> February 5, 2000 <br /> Page 8 <br /> The submersible pump was cleaned with a solution of Liqui-nox® and water prior to purging <br /> each well to minimize the potential for cross-contamination. In addition, the wells were sampled <br /> in order of increasing concentration based on previous sampling results. All water removed <br /> during sampling and purging operations was placed in sealed and labeled 55-gallon drums and <br /> stored on site. <br /> Analysis of water samples MW2, and MW6 revealed no detectable concentrations of TPH as <br /> gasoline, BTEX, or oxygenates. <br /> Concentrations of TPH as gasoline were detected in the water samples obtained from wells <br /> MWI., MW4 and MW5 at concentrations of 430 pg/l, 1,200 µg11, and 19,000 gg/l, respectively. <br /> Benzene was detected in MW4 and MW5 at concentrations of 69 µg11 and 3,300 gg/1, <br /> respectively. Review of historic data reveals no specific trend with regard to TPH as gasoline <br /> = concentrations in wells MW4 and MW5. Concentrations of TPH as gasoline in well MW1 have <br /> decreased dramatically from historic levels but remain sporadic since 1999. <br /> MTBE was only detected in wells MWl (2.2 µg/1),MW3 (1.6 gg/1) and MW4 (0.68). Tert- <br /> Butanol was additionally reported in MWl at a concentration of 7.8 ug/L. And finally, 1,2 <br /> Dichloroethane was reported for the first time at this site in wells MW 1 (2.2 ug/L), MW5 (44 <br /> ug/L) and MW7 (0.74 ug/L)..The origin of this compound is not known. Laboratory data is <br /> summarized on Tables 2 and 3 with complete laboratory results and chain of custody documents <br /> are included as Appendix C. <br /> Conclusions <br /> Vapor extraction pilot test data indicate an effective radius of influence of at least 23 feet may be <br /> achieved at the site using a vacuum pressure of at Ieast(36-in ches H2O d a flow rate oI_)__ <br /> scfi:n beneath the site. Maximum observed vacuum pressure drawdown in the observation wells <br /> ranged from 1.4 to 2.5 inches of water. Our experience has demonstrated that an observed <br /> vacuum pressure of at least 0.4 inches of water column in the observation wells indicates that the <br /> well is within the zone of influence of the vacuum applied at the vapor extraction well. <br /> INK <br /> WALLACE 1WHI, <br /> R"dJp„�, @fklti.�Sf�CIA7F=� IIdC;.. <br />