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. The vapor extraction system continued to work through the months of October, November and December 1997 with a brief shut down in December for quarterly monitoring. The system has operated a total of 15,449 hours (644 days as of December 22, 1997). Vapor extraction total removed hydrocarbons as gasoline using activated carbon as a control was 223 pounds, averaging 0.39 pounds per day at an average concentration of 0.208 mg/L, and an average flow rate of 67 cubic feet per minute (cfm). On October 3, 1997, after concurrence with San 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 Table 2 and Appendix C — Field notes/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 5 pounds Total Removal 75,077 pounds or approximately 11,585 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 MW 12 to conduct bio venting. As of December 30, 1997 the 2 hour once a week bio venting of MW-8 has removed a calculated 5.06 pounds of gasoline range hydrocarbons and a total of 462 pounds of hydrocarbons as gasoline and CO2. The average flow rate is 50.8 cfm, with a vapor stream consisting of TPHg of 0.001 mg/L and CO2 at 1.5%, see Table 4 and Appendix D. Summary SOIL Confirmation soil sample borings SB4, SB5, SB6 and SB7 were drilled and sampled (June 1997) near previous sample boring SBI, SB2 and SB3 (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 Tesults. No MTBE was noted in any of the soil samples. Comparing the historic highest contaminated depth, fifty feet below ground surface (bgs), the following reductions in contaminants are noted and are representative of the overall site conditions: S134 compared to SB I showed a 99.7% reduction of gasoline range hydrocarbons (TPHg), complete removal of benzene and toluene, and a 99.8% reduction of the xylenes. 5 8603 Update#50 12/97