ARCHIVED REPORTS_XR0007462 CASE 1

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REQ[TEST FOR SITE CLOSURE Gcneral Mills FacLry :000 wesi Turner Road • i.adx irrua FJGiCB ProjPR7JCCL NO 40-92-7,08 Page 5 for xvienes Ot course, an analysis using benzene was not performed because benzene has not been detected in any soil sample collected at the site, both during the tanic removal in October 1991 and the soil boring investigation ui May 1992 The following site data were used in the analyses average annual rainrall in Loai, California, depth to ground water in site monitoring wells, and sod cherrucal analyses data. The average annual rainrall according to the City of Lodi Chamber of Commerce is 16 62 inches The smallest recorded distance from the surface to ground water m monitoring wells at the site is 39 -' feet (Table 3) Sample T5-M, collected from the case of the tank excavation at a depth of 15 feet, had the highest concentrations of toluene (0 006 ppm), xylenes (0 045 ppm), ethylbenzene (0 01 ppm), and TPH as diesel (820 ppm) Our General Risk Appraisal Analyses are presented in Appendix A. The results inaicate that acceptable concentrations of toluene, xylenes, and ethylbenzene at the base of the tank excavation (15 feet) are S. 30, and 40 ppm, respectively As can be seen, these concentrations are well above the concentrations detected in the base of the tank excavation. It is Delta's opinion that petroleum constituents have not migrated vertically beneath the tank excavation. Subjective analyses of soil samples collected between I5 and 30 feet from the sou oarmg for monitoring well 1dzN-3, advanced through the tormer tank basin, did not detect the presence of petroleum hydrocarbons. Also, Iaboratory analysis of the sample collected at 35 feet did not detect the presence of these constituents. However, it has been suggested by the County that subjective analyses of soil samples were not adequate. 'Therefore, m an effort to determine what the acceptable concentrations of toluene, xylenes, and ethylbenzene would be if these constituents have migrated vertically between 15 and 30 feet, Delta performed additional General Risk Appraisal Analyses For these analyses we assumed a worst case: toluene, xylenes, and ethylbenzene have migrated vertically at the same concentrations as detected in the soil sample collected at 15 feet. Although we do not believe that this has occurred, we find that if it had, the acceptable concentrations at 20, 25, and 30 feet are still well above the concentrations detected m the base of the tank excavation. These theoretical analyses are presented cn . Appendix B gp'r076 TA