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R603 UPDATE-12 12/22/92 1 . 0 INTRODUCTION This update, STATUS UPDATE #12, represents data collected at the site from November 17, through December 18, 1992 . During this time, a thermal oxidation unit was operating and vapor extraction for soil and ground water remediation was taking place . The December quarterly ground water samples were also obtained. The permit to dump treated ground water to the sewer was received and presently we are batch dumping the treated water from the "ConVault" monthly This water is collected from the vapor recovery condensate dropouts and the twice weekly purging of monitor wells MW1, MW2, MW3 , MW8 and MW10 by Lawrence Tank Testing (LTT) pumping service Once the ground water recovery - treatment system has been completed, pumping will occur from monitor wells MW1 and MW3 1 . 1 LOCATION The station is located at 6425 Pacific Avenue at the intersection of Douglas Road, in San Joaquin County, Stockton, California The site lies in Section 21, T2N, R6E; MDB&M at approximately 12 feet above mean sea level (MSL) (see Figures 1, 2 , 3) The parcel is # 31 and can be located in Assessor' s Book 97 on page 41 (97-041-31) . On October 2 , 1992, a licensed surveyor with Nolte & Assoc . surveyed all monitoring well locations and top of casing elevations to a known datum, City of Stockton Bench Mark Number 12, elevation 11 74 ' above mean sea level . 1 . 2 PREVIOUS REPORT UPDATE STATUS REPORT 11 OCTOBER- NOVEMBER 1992 UPDATE STATUS REPORT . The following are the conclusions and recommendations of the previously submitted UPDATE STATUS REPORT #11 • DISCUSSION AND CONCLUSIONS As stated in earlier reports, the soil is contaminated with gasoline range hydrocarbons beneath the tank field (MW10) and _ a �-,,,.. along the capillary fringe of tsi._e ground wate , r +�wrr,�1, MW") MW3 and MW10) , see Figure 6 Ground water beneath the site contains the dissolved constituents of gasoline range hydrocarbons and has spread out from beneath the site to the north (MW-6) , to the The south (MW-7) to the west (MW-9) and to the east (MW-8) . in,--St cqrr,,,nei water sampling, September 22, 1992 , has shown- -a decline in the lateral extent of the plume, see Figure 5 (9-22- 92) . Vapor extraction commenced on October 17, 1991 and until November 17i 1992 has operated for 5388 hours out of a possible 8821 . 5 for a 61% run time, destroying 39, 542 pounds of gasoline range hydrocarbons . Since the last status report, October 16 , 1992 , a total of 5176 pounds of gasoline range hydrocarbons have been removed/destroyed in 524 hours of operation (9 . 88 pounds per hour PAGE 1