ARCHIVED REPORTS_XR0007460 CASE 1

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RE!2n= FOR SITE CLOSURE General Mills Factltty 2000 Wesc Turner Road Lodi Cnluorrua Delta Project No 40-92-708 Page a for xylenes 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 tank removal in October 1991 and the 1 soil boring investigation In May 1992 ' The following site data were used in the analyses average annual rainfall in Low, Californua, depth to ground water in site motutoring wells, and soil chemical analyses data. The average annual rainfall ' 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 a feet (Table 3) Sample T5-M, collected from the base of the tank excavation at a depth of 15 feet, had the highest concentrations of toluene (0 006 ppm), xyienes (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 indicate that acceptable concentrations of toluene, xyienes, and ethyibenzene at the base of the tank excavation (15 feet) are 8, 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 opimon that petroleum constituents have not migrated vertically beneath the tank excavation. ' Subjective analyses of soul samples collected between 15 and 30 feet from the sod boring for monitoring well MW-3, advanced through the former tank basin, did not detect the presence of petroleum ' hydrocarbons. Also, laboratory analysis of the sample collected at 35 feet dad 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, in an effort to determine what the acceptable concentrations of toluene, xylenes, and ethyibenzene 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 iia 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 in the base of the tank excavation These theoretical analyses are presented in Appendix B ' RpTC176 TA