ARCHIVED REPORTS XR0006515 - Laserfiche WebLink

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MW 10, which contained free product until November 1992, has not exceeded therima MCLs for P rY Benzene since December 1996, for Toluene since March 1994, for Ethylbenzene since March 1993 and for Xylenes since March 1995 The secondary MCLS for Toluene and Ethylbenzene have not been exceeded since December 1994 and September 1995 respectively MW12, which is downgradient of MW8, has not exceeded the primary MCLS for Toluene since March 1996 and for Ethylbenzene since December 1996 MTBE has only been found and confirmed in the offsite wells MW8, MW11 and MW12 Confirmations of the MTBE using EPA Method 8260 indicate that concentrations are below 45 ug/L MTBE was the only Oxygenant found in the December 1997 sampling and only in MW11, at 3 0 ug/L Update of groundwater contaminant plume migration controls Groundwater plume containment is being provided by vapor extraction of MWl, MW2, MW3 and MW10, by oxygenation of the groundwater by sparging MW2 and MW13 and by weekly purging and venting of MW8 and MW12 by Lawrence Tank Testing, see Appendix D MW8 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 Table 3 Vapor extraction has reduced the contaminant levels in the soil and groundwater Fluctuating groundwater elevations most likely influence fluctuations in groundwater contaminant concentration levels Update of Vapor Extraction System Operation The vapor extraction system continued to work through the months of December 1997, January, February, and March 1998 A brief shut down occurred for quarterly monitoring (March 10 - 11, 1998) The system has operated a total of 17612 hours (734 days as of March 23, 1998) Vapor extraction total removed hydrocarbons, as gasoline using activated carbon as a control was 223 pounds and direct venting to atmosphere of 9 8 pounds For this quarter (January-March, 1998) the VES averaged 0 03 pounds per day removal at an average concentration of 0 003 mg/L, and an average How rale of 65 cubic feet per minute (cfin) 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 4 and Appendix C -- Field notes/Chromatograms Previous vapor extraction removals were controlled by Thermal Oxidation and removed 74,849 pounds of gasoline range hydrocarbons 4 R603 Update#51 5198