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' Fourth Quarter 2004 Groundwater Report 8200 N Highway 99, Stockton, CA Page 5 of 6 ' pounds of MTBE, were removed through the treatment system Groundwater in the shallow aquifer beneath the site generally flowed to the northeast when ' monitored on December 14, 2004, although a pumping depression was evident around the extraction wells (MW 1 and EW2) ' MTBE was detected in downgradient A Zone well MW12 on December 16, 2004 No MTBE was detected in wells MW10 or MW11, located west of well MW12, or in wells MW15 and MW16, which are located downgradient of well MW12 ' MTBE was detected in the C Zone well MW13C, unlike the previous reporting period in September 2004, when MTBE was not detected Well MW13C is located east of the former ' water supply well No MTBE was detected in B Zone well MW14B, which is located within a few feet of the former water supply well ' 5.0 CONCLUSIONS ' Dissolved MTBE in the shallow aquifer beneath the site does not extend to the nearby residences, as evidenced by non-detect results in wells MWI5 and MW16 Groundwater extraction appears to be reducing the concentration of gasoline constituents in well MW1 and nearby monitoring wells MW3 and MW4, which are located approximately 51 feet and 56 feet, respectively, from the extraction well MTBE has been detected at relatively low levels in C Zone monitoring well MW13C, which is completed to a depth of approximately 222 feet bgs, but has not been detected in B Zone well ' MW1413, which is completed to a depth of approximately 124 feet bgs Well MW913, completed to a depth of approximately 110 feet bgs, also contains no petroleum hyrdrocarbons ' Based upon analytical results of influent and effluent samples collected at the site, no carcinogenic PAHs are present in groundwater beneath the site In addition, the inorganic constituents chloride, nitrate, sulfate, total dissolved solids (TDS), specific conductance (EC), Iand pH are within acceptable ranges 6.0 RECOMMENDATIONS ' Based upon consistent non-detect results in B Zone wells MW9B and MW14B, Ground Zero recommends that these wells be destroyed under permit from EHD These wells have demonstrated that the B Zone aquifer beneath the site (approximately 105-125 feet bgs) has not been impacted by the dissolved contaminant plume Based upon results of influent and effluent samples collected since November 2003, Ground 11GZA_FSIVOL_i1PATAIGROUNDZEITULEBURG%Reports\QMR1200414QM2004 doe