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SITE CLOSURE RE UEST REPORT Former Exxon Service Station No.7-3330 3128 West Benjamin Holt Drive Stockton,California Delta Project No. D093-810 Page 9 Concentrations of total oil and grease were detected at concentrations of 60 and 77 mg/kg at two locations (WO1 and W02, respectively) at the limits of the excavation of the former used oil tank (Table 5). The areas located along the limits of the excavation of the former product islands reporting TPH as gasoline at concentrations of 25, 210 and 53 mg/kg, appear to be isolated as indicated by soil sample analytical results from soil borings SB-3 through SB-8 (Table 1, Figure 5). Figure 10 illustrates the estimated area of TPH as gasoline impacted soil. Utilizing the inferred lateral and vertical extent of residual hydrocarbons, reported analytical results, and the model illustrated in Figure 11, the total volume of liquid phase hydrocarbons quantified as gasoline is calculated to be 2.58 pounds, which equates to approximately 0.42 gallons remaining in soil. The residual TPH quantification calculations are included in Appendix A. iThe benzene impacted soil along the limits of the product island excavations appear to be isolated in the vicinity of soil samples PL-1, PL-2, and PL-3, as indicated by results from samples collected in soil borings SB-3 through SB-8 (Table 1, Figure 5). The extent of the estimated benzene impacted soil is illustrated in Figure 12. Using the model illustrated in Figure 12, analytical results, and the calculations included in Appendix A, an estimated 0.0136 pounds of benzene, which equates to approximately 0.0019 gallons, remains in soil. During the December 1991 and May 1992 overexcavation of the tank basin and product islands, approximately 1,750 cubic yards of soil was removed and transported off-site. The excavated soil contained approximately 94 pounds of TPH as gasoline and approximately 0.5 pounds of benzene. The total soil volumes and concentrations from the excavation activities are included in Table 6. The calculations for estimated hydrocarbons removed by excavation is included in Appendix B. The estimated pounds of TPH as gasoline remaining in soil is approximately 2.58 pounds, and the estimated pounds of benzene remaining in soil is approximately 0.0136 pounds. The estimated percentage of TPH as gasoline and benzene removed by excavation from the site is 97.4 and 97.3 percent, respectively. The calculations for percentage of hydrocarbons removed is included in Appendix C. RPT001.810