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the VES averaged 0.02 pounds per day removal at an average concentration of 0.003 mg/L, and an average flow rate of 60 cubic feet per minute (cfrn). On October 3, 1997, after concurrence with Saul Joaquin Valley Air District, the four 110 gallon vapor scrub units were removed from the treatment system and the offgass from the vapor recovery system was vented directly to the atmosphere, see Appendix D — Tables, Field notes and Chromatograms. Previous vapor extraction removals were controlled by Thermal Oxidation and removed 74,849 pounds of gasoline range hydrocarbons. Totals of gasoline range hydrocarbons removed by the vapor extraction system are as follows: Thermal Oxidation destruction 74,849 pounds Carbon Adsorption 223 pounds Vent to atmosphere 11 pounds Total Removal 75,083 pounds or approximately 12,013 gallons. Weekly bio-venting of MW-8 and MW-12 are being conducted by Lawrence Tank Testing. Currently the groundwater is too high; no slotted casing is exposed above groundwater at MW12 to conduct bio venting. As of June 22, 1998 the 2 hour once a week bio venting of MW-8 has removed a calculated 5.38 pounds of gasoline range hydrocarbons and a total of 506 pounds of hydrocarbons as gasoline and CO2. The average flow rate is 50.8 cfm, with a vapor stream consisting of TPHg of 0.02 mg/L and CO2 at 0.5%, see Table 5 and Appendix E. i Summary SOIL Confirmation soil sample borings S134, S135, S136 and S137 were drilled and sampled (June 1997) near previous sample boring SBI, S132 and S133 (December 1988), see Figure 3. Charts were developed to show the reduction comparisons of the soil sample results, see previous report CONFIRMATION OF THE EFFECTS OF THE VAPOR EXTRACTION SYSTEM, dated July 31, 1997, Table 2 for results. No MTBE was noted in any of the soil samples. The following four comparisons are from the 50 foot depth, which is the depth of the historic highest concentrations. I. S134 compared to SBI showed a 99.7% reduction of gasoline range hydrocarbons (TPHg), complete removal of benzene and toluene, and a 99.8% reduction of the xylenes. 2. S137 compared to MW2 and MW3 respectively showed the following reductions: TPHg at 96.9% and 99%, Benzene and Toluene complete removal, and Xylenes at 90.5% and 99%. 3. S135 compared to MW2 and MW3 respectively showed the following reductions: TPHg at 98.38% and 99.48%, Benzene, Toluene and Ethylbenzene complete removal, and Xylenes at 96.29% and 99.61%. 4. SB6 compared to S133 (highest noted contaminated area) and MW10 respectively, showed the following reductions: TPHg at 99.2% and 96.6%, Benzene, Toluene and Xylenes complete removal. 7 8603 Update#52/CLOSURE RV 7/98