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SI'Z'E CLOSURE REPORT <br /> General Mills, Inc <br /> 2000 West Turner Road <br /> Lodt, Caltfortna <br /> Delta Project No D092-708 <br /> Page 2 <br /> storage tanks (USTs) as a preemptive measure for possible fuel shortages According to the General <br />' Mills engineer in charge of the tank replacement project, oil-stained soil was observed, however, no <br /> standing oil was present <br />' The three 12,000-gallon USTs were used to store No 6 heating oil The tanks were removed between <br />' October 11, and 17, 1991 After removing the tanks, the excavation of soil was contracted to Stockton <br /> Service Station Equipment Company of Stockton, California. Following the excavation of soil, the tank <br />' excavation was backfilled from 15 feet bsg to approximately 5 feet bsg with well-graded gravel, and the <br /> remaining 5 feet was backfilled with silty sand <br />' On May 12, 1992, Delta observed the drilling of three soil borings to 50 feet bsg These borings were <br /> completed as ground water monitoring wells MW-1, MW-2, and MW-3 The results of this investigation <br /> are presented in Delta's Hydrogeologic Investigation Report, dated June 9, 1992 Ground water <br /> monitoring wells MW-1, MW-2, and MW-3 have been monitored since their installation in May 1992 <br /> Quarterly ground water sampling was conducted at the site for four consecutive quarters (May 1992 <br /> through March 1993), at which time the County, in their letter dated July 27, 1993, agreed to a request <br /> to reduce the monitoring well sampling frequency to semi-annual, provided that no petroleum <br /> hydrocarbons were detected <br /> In a letter dated February 17, 1993, the County requested that additional site assessment be performed <br />' at the site In this letter, the County stated that after evaluating soil with hydrocarbon concentrations <br /> remaining in place using the Leaching Potential Analysis, that additional investigation was required <br /> between 15 feet bsg and the top of ground water Delta responded to the County's request by presenting <br /> a Leaching Potential Analysis, in a letter dated March 18, 1993, utilizing information collected during <br />' the hydrogeologic investigation conducted at the site Delta's analysis indicated that the maximum <br /> allowable total petroleum hydrocarbon (TPH) as diesel No. 6 (heating oil) concentration that could be <br />' left in place without posing a threat to ground water quality at 15 feet bsg (tank basin floor) is 1,000 parts <br /> per million (ppm) <br />' RPT 137 S!s <br />