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dispensers and drained the product lines in July 1998 On July 31, 1998, LTT tripled rinse the product lines and the UST's, removed the rinseate from the UST's and placed the rinseate in the ConVault for air stripping Prior to discharging this water to sewer a sample was obtained on August 16, 1998 and showed that the treated water met the City of Stockton Sewer Discharge Requirements, see Appendix C Since that time there has been no product in the product dispensing and storage system at this site Update of groundwater contaminant plume migration controls Groundwater plume containment is being provided by vapor extraction of MW 1, MW2, MW3 and MW10, by oxygenation of the groundwater by air sparging MW2 and MW 13 and by weekly purging and venting of MW8 and MW12 by Lawrence Tank Testing MWS and MW12 are purged of approximately 40 and 70 gallons per week respectively This purged groundwater is stored on site in the 1000 gallon ConVault and is air stripped prior to discharge to the City of Stockton's sewer system under permit, see Sewer Discharge Reports—Appendix C Vapor extraction has reduced the contaminant levels in the soil and groundwater and air sparging of MW2 and MW13 have enhanced biodegradation and reduced concentrations in wells MW2, MW8 and M W 12 Update of Vapor Extraction System Operation The vapor extraction system continued to work through the months September, October, November and December 1998 Shutdowns occurred for quarterly monitoring (November 12 - 18, 1998) The system has operated a total of 21884 hours (912 days as of December 10, 1998) Vapor extraction total removed hydrocarbons, as gasoline using activated carbon as a control was 223 pounds and direct *venting to atmosphere of 19 pounds For this quarter (October - December 1998) the VES averaged 0 01 pounds per day removal at an average concentration of 0 001 mg/L, and an average flow rate of 67 cubic feet per minute (cfm), see Table 2 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 offgas from the vapor recovery system was vented directly to the atmosphere, see Appendix D — Field notes and Chromatograms Previous vapor extraction removals ,A ere 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 19 pounds Total Removal 75,091 pounds or approximately 12,014 5 gallons 6 R603 Update#54/CLOSURE 3 12198