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SITE CLOSURE REQUFSr REPORT Fortner Exxon Service Station No.7-3330 3128 West Benjamin Holt Drive Stockton,California Delta Project No. D093-810 Page 13 first hour of the test. A second sample was collected during the fourth (final) hour of the test. Both samples were analyzed for TPH as gasoline and BTEX. Laboratory analytical results from the initial sample (MW-5A) reported TPH as gasoline and benzene concentrations to be below the laboratory's detection limits. Analytical results from the final sample (MW-5B) reported TPH as gasoline at 4.3 parts per million by volume (ppmv), and benzene at 0.024 ppmv. The results of the laboratory analyses are summarized in Table 7, and a copy of the laboratory analytical report is included in Appendix G. The following field data was recorded during the four hour SVE pilot test: SVE flow velocity, soil vapor hydrocarbon concentrations as measured by a flame ionization detector (FID), and vacuum influence in two surrounding observation (monitoring) wells. Vacuum influence data measured in the observation wells during each test is summarized in Table 8. A copy of the field data sheet is included in Appendix H. Measurable vacuum influence was not detected during the SVE pilot test in either nearby observation wells (MW-4 and MW-C). Calculations to estimate the soil vapor flow rate and hydrocarbon extraction rate from the test well during the pilot test are included in Appendix I. The mass flow rate, along with the induced test well vacuum is summarized in Table 9. The test well vacuum was approximately 9.0 inches of water column. This low vacuum was used to control the level of the ground water and prevent the ground water from covering the well screen. Due to the well screen interval, depth to ground water, low permeability of the soil (predominately clays in the upper soil horizon), the lack of vacuum influence in the surrounding wells, and the vapor concentrations of 4.3 ppmv as gasoline from the SVE test, the test indicates that SVE was not a technically effective or cost effective remediation technology in reducing the limited areas of impacted petroleum hydrocarbons underlying the site. 6.0 BIODEGRADATION Natural attenuation and passive bioremediation are remedial processes that utilize natural processes to dissipate and degrade petroleum constituents in soil and ground water. Some of the processes involved RPT001.810