ARCHIVED REPORTS_XR0007461 CASE 1

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SITE 2LOSURE REPORT General Mills, Inc 2000 west Turner Road Lodi, California Delta Project No D092-708 Page 3 On April 15, 1993, representatives from the County, Delta, and General Mills discussed appropriate actions for the site It was concluded that the variation between the County's and Delta's Leaching Potential Analyses was based on the depth to ground water The County utilized a minimum depth to ground water from the soil samples containing TPH as diesel No 6 of less than 25 feet resulting in a maximum in place hydrocarbon concentration of 100 ppm Delta utilized a depth to ground water in excess of 25 feet, resulting in a maximum allowable in place hydrocarbon concentration of 1,000 ppm Due to the discrepancy, the County suggested that Delta present its case for leaving soil in place with concentrations of TPH as diesel No 6 over 100 ppm to the Technical Advisory Committee Delta performed a General Risk Appraisal, which is considered by the LUFT manual guidelines to be "more sophisticated than the leaching potential analyses" for evaluating the risk of ground water pollution at an underground fuel tank site for benzene, toluene, ethylbenzene, and xylenes (BTEX) concentrations in soil The Risk Appraisal Analysis conducted for toluene, xylenes, and ethylbenzene indicated that the acceptable concentrations for these constituents at a depth of 15 feet below grade were 8, 30, and 40 ppm, respectively A Risk Appraisal Analysis for benzene was not performed since benzene had not been detected in the soil samples collected at the site Delta also performed a "worst case scenario" Risk Appraisal Analysis which assumed that toluene, xylenes, and ethylbenzene had migrated vertically at the same concentrations detected at 15 feet, these findings indicated that the concentrations detected at 15 feet would still be acceptable at 20, 25, and 30 feet bsg Delta submitted a Request for Site Closure Report, dated September 3, 1993, to the County which summarized Delta's findings, including Leaching Potential Analysis and Risk Appraisal Assessments However, the County did not approve the request for closure and required that additional soil samples be collected to further evaluate the vertical extent of petroleum hydrocarbons in soil immediately beneath the former tank basin In response to this request, Delta submitted a Work Plan for Additional Drilling, dated April 12, 1994, which proposed the installation of three additional soil borings in the vicinity of the former tank basin The County approved the work plan in a letter dated April 28, 1994, in which they stated that "based on site specific conditions, soil type, location and seasonal depth to ground water, • RPT137 S!S