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lei Case Closure Report Former Tosco(Unocal) SS No 5421, Stockton,California July 8, 1998 •} Analytical results of vapor piping trench samples indicated non-detectable levels of TPH as gasoline for sample VI and 4 2 ppm of TPH as gasoline for sample V2, with non- detectable levels of EDB in each sample The waste oil tank bottom soil sample (WO1) and the waste oil remote fill piping sample (WP 1) both showed non-detectable levels of TEPH and all EPA Method 8010, 8020, and 8030 constituents Analytical results of the water sample collected from a on-site water well indicated 160 parts per billion (ppb) of TPH as gasoline, with non-detectable concentrations of all other analytes The analytical results and location of the samples collected from the old and new fuel tank pits, the product pipe trench, the vapor pipe trench the waste oil tank bottom and the remote fill piping soil samples are presented in Appendix A Table IA, Figure 2A The analytical results for the water sample is also presented in Appendix A Table 3A To comply with the requirements of the regulatory agencies and based on the analytical results, KEI proposed the installation of four monitoring wells Results of the soil samples from the tank excavation are summarized in KEI's report (KEI-P89-1104 RI) dated January 8, 1990 Phase I Site Assessment Activities On October 10 an 11, 1990, four two-inch diameter monitoring wells (designated as MW- 1, MW-2, MW-3, and MW-4) on the attached Figure 2 were installed at the site The monitoring wells were drilled and completed to total depths ranging from 69 to 74 feet below grade Groundwater was encountered at depths ranging from 58 5 to 59 5 feet below ground surface (bgs) during drilling Well elevations were surveyed by a licensed land surveyor to Mean Sea Level (MSL) and to a vertical accuracy of 0 01 feet The wells were developed on October 18, 1990, and were initially sampled on October 26, 1990 Selected soil samples and all water samples were analyzed for TPH as gasoline and BTEX In addition, the samples collected from MW-1 (adjacent to the waste oil tank pit) were analyzed for TPH as diesel, total oil and grease (TOG), and EPA Method 8010 constituents Analytical results of soil samples collected from the borings for monitoring wells MW-i through MW-4 indicated non-detectable levels of TPH as gasoline and benzene in all soil samples, except for sample MW-3 at 30 5 feet bgs, which showed 0 088 ppm of benzene In MW-1, TPH as diesel, TOG, and all EPA Method 8010 compounds were non- detectable in all soil samples, except for sample MW-1 at 10 feet bgs, which contained 76 ppm of TOG • 140162 03 4