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The most recent groundwater monitoring sampled all wells (MW I through MW 13), except MW4, <br /> which was not accessible These samples were analyzed for Total Petroleum Hydrocarbons as <br /> gasoline (TPHg), Benzene Toluene, Ethylbenzene, Xylenes and Methyl tertiary Butyl Ether <br /> (1\1BTE`Y) using EPA method 8260B and Dissolved Lead using EPA method 200 8 <br /> Water samples from MW1, MW3, MW5, NM16, MW7, MW9, MW1I and NIW12 tested below <br /> laboratory detection limits for BTEX (0 5 ug/L) <br /> Water samples from MW1, MW3, MW5, MW6, MW7, MW9, and MW1 l tested below laboratory <br /> lower detection limits for TPHg (50 ug/L) <br /> All wells tested below laboratory lower detection limits (5 ug/L) for dissolved lead, see Table 1 and <br /> Appendix C <br /> The groundwater plume of dissolved gasoline range hydrocarbons has been reduced in size and <br /> concentrations <br /> Fid^ure 3 represents TPHg, BTEX and MTBE measurements obtained December 12 and 15, 2000 <br /> Table 1 represents groundwater chemical results showing TPHg, MBTEX and DO <br /> . Currently only MW2 exceed the primary MCLs for Benzene in drinking water standards for the <br /> State of Calfironia at 16 ug/L <br /> MTBE was found in the wells MW2 at 1 8 ug/L, MW 10 at 0 69 ug/L, MW I 1 at 38 ug/L and MW 13 <br /> at 25 ug/L MTBE was the only Oxygenant found in the December 1997 sampling and only in <br /> MW1 1 at 30 u(y/L <br /> Update of groundwater contaminant plume migration controls <br /> Groundwater plume containment was being provided by vapor extraction of MW 1, MW2, MW3 and <br /> MW 10, by oxygenation of the groundwater by air sparging MW2 and MW 13 The vapor extraction <br /> system and sparging system was turned off December 19, 1998 Weekly purging and venting of <br /> MW8 and MW 12 by Lawrence Tank Testing was terminated on December 14, 1998 MW8 and <br /> MW12 were purged of approximately 40 and 70 gallons of water per week, respectively Ties <br /> purged groundwater is stored on site in the 1000 gallon ConVault and is air stripped prior to <br /> discharge to the City of Stockton's sewer system under permit, see Sewer Discharge Table 4 <br /> ELECTRON ACCEPTORS <br /> Natural Attenuation is occurring at this site Field groundwater analysis obtained December 16, , <br /> 1997 for Dissolved Oxygen, Nitrate, Sulfate and Ferrous Iron demonstrate that the available oxygen <br /> is being used by microorganisms and a reducing environment has been established at MW2 with the <br /> onset of methogenisis During the January 1999 sampling Dissolved Oxygen, Nitrate, Sulfate, <br /> 2 R603 Update #�6 12/2000 <br />