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SITE CLOSURE REQUEST REPORT Former Exxon Service Station No. 7-3330 3128 West Benjamin Holt Drive Stockton,California Delta Project No. D093-810 Page 8 Depth to ground water has ranged from 7.11 to 16.48 feet below the top of the well casings. These variations have been associated with seasonal fluctuations. Using the ground water level measurements, ground water contour maps have been prepared. The ground water flow direction has consistently been toward the northeast (Figure 9), with a gradient of less than 0.01. Ground water samples have been collected from the monitoring wells and submitted for laboratory analysis of BTEX and TPH as gasoline using the previously described methods. Cumulative ground water analytical results are summarized in Table 3. 3.0 DISTRIBUTION OF PETROLEUM HYDROCARBONS IN SOIL Based on confirmation soil sample analytical results, soil in the vicinity of the former tank areas containing residual concentrations of petroleum hydrocarbons has been sufficiently excavated and removed from the site. Confirmation samples (S-1 through S-10) collected at the limits of the overexcavation in the area of the former USTs (Figure 5) did not contain detectable concentrations of TPH as gasoline, toluene, or ethylbenzene. Slight concentrations of benzene and total xylenes were reported in two samples. A summary of the analytical results are presented in Table 4. Confirmation soil samples (PI-1 through PI-12) were collected from the limits of the former pump island excavation (Figure 5). Analytical results reported that soil with detectable concentrations of petroleum hydrocarbons had been overexcavated from the dispenser area with the exception of isolated areas. Soil samples PI-1, PI-2, and PI-3 collected along the eastern and southeastern limits of the excavation reported concentrations of TPH as gasoline at 25, 210, and 53 milligrams per kilogram (mg/kg), respectively. Soil sample PI-5 collected along the northwestern corner of the excavation contained concentrations of TPH as gasoline at 26 mg/kg. All other samples collected at the limits of the excavation of the former pump island locations did not contain detectable concentrations of TPH as gasoline. Benzene concentrations in soil samples PI-1, PI-2, and PI-3 were detected at 0.057, 0.9, and 0.33 mg/kg, respectively. All other confirmation samples did not contain detectable concentrations of benzene. ►� i RPT001.810