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REQUEST FOR SITE CLOSURE <br /> Genera! 1Aii.13 Facility <br /> 2000 West Turner Road <br /> Lodi Caldorma <br /> Delta Project No 40-92 7 08 <br /> Page 5 <br /> for xvienes Of course, an analysis using benzene was not performed because benzene has not been <br /> de an soil sample collected at the site both during the tank removal in October 1991 and the <br /> detected in y p , <br /> soil boring investigation in May 1992 <br />' Tine following site data were used in the analyses average annual rainfall in Lodi, California, depth to <br /> ground water in site monitoring wells, and soil chemical analyses data. The average annual rainfall <br />' according to the City of Lodi Chamber of Commerce is 16 62 inches The smallest recorded distance <br /> from the surface to ground water in monitoring wells at the site is 39 4 feet (Table 3) Sample T5-M, <br /> collected trom the base of the tank excavation at a depth of 15 feet, had the highest concentrations of <br />' toluene (0 006 ppm), xylenes (0 045 ppm), ethyibenzene (0 01 ppm), and TPH as diesel (820 ppm) <br /> Our General Risk Appraisal Analyses are presented in Appendix A. The results indicate that acceptable <br /> concentrations of toluene, xylenes, and ethyibenzene at the base of the tank excavation (15 feet) are 8, <br /> 30, and 40 ppm, respectively As can be seen, these concentrations are well above the concentrations <br /> detected in the base of the tank excavation <br /> It is Delta's opinion that petroleum constituents have not migrated vertically beneath the tank excavation. <br /> Subjective analyses of soil samples collected between 15 and 30 feet from the soil boring for monitoring <br /> well MW-3, advanced through the tormer tank basin, did not detect the presence of petroleum <br />' hydrocarbons. Also, laboratory analysis of the sample collected at 35 feet did not detect the presence <br /> of these constituents. However, it has been suggested by the County that subjective analyses of soil <br />' samples were not adequate Therefore, in an effort to determine what the acceptable concentrations of <br /> toluene, xylenes, and ethylbenzene would be if these constituents have migrated vertically between 15 <br />' and 30 feet, Delta performed additional General Risk Appraisal Analyses For these analyses we assumed <br /> a worst case: toluene, xylenes, and ethylbenzene have migrated vertically at the same concentrations as <br />' detected m the soil sample collected at 15 feet. Although we do not believe that this has occurred, we <br /> find that if it had, the acceptable concentrations at 20, 25, and 30 feet are still well above the <br /> concentrations detected in the base of the tank excavation. These theoretical analyses are presented in <br /> Appendix B <br />' PJgW6 TA <br />