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+l <br /> ATTACHMENT B <br /> SUMMARY OF PREVIOUS INVESTIGATIONS (CONTINUED) <br /> Chevron Service Station 9-2033, 508 West Charter Way, Stockton, California <br /> Groundwater analytical results for water samples collected from SB-2 suggest increasing <br /> concentrations of TPHg from 790 gg/L at 46 5 feet bgs to 3,100 gg/L at 54 feet bgs Results <br /> for groundwater at 82 feet suggest no TPHg was present Similar trends were noted for <br /> BTEX and TBA Groundwater analytical results for water samples collected from SB-2 <br /> suggest a decrease of TPHg, BTEX and fuel oxygenate concentrations throughout the profile <br /> Concentrations of MtBE were typical of this trend 46,000 gg/L at 35-feet bgs, 160 gg/L at <br /> 62 5-feet bgs and 6 0 gg/L at 86 5-feet bgs Groundwater analytical results for water samples <br /> collected from SB-4/CPT-02 suggest an increase of TPHg from 840 gg/L at 44-feet bgs to <br /> 1,200 gg/L at 54-feet bgs Benzene concentrations at these same depths increased from 22 <br /> gg/L to 84 gg/L Ethylbenzene and xylene concentrations were approximately equal at these <br /> depths and MtBE and TBA decreased with depth No analytes were detected in the 83-foot <br /> sample from SB-4 <br /> Quarterly sampling of monitoring wells MW-1 through MW-3 has been performed since <br /> May 1995 Dissolved concentrations of TPHg in MW-1 increased from 340 to 5,900 <br /> micrograms per Liter (µg/L) during this period Dissolved benzene concentrations in MW-1 <br /> have also increased from 67 gg/L in May 1995 to 1,100 jig/Lin August 1997 Review of <br /> MW-1 analytical results also suggests an increasing trend in 1,2 dichloroethane (DCA) <br /> Analytical results for MW-2 have consistently indicated no detectable concentrations of <br /> TPHg, BTEX, and MtBE Review of analytical results for MW-3 suggests a decreasing <br /> trend of hydrocarbon concentrations between May 1995 and August 1997, from 44,000 lig/L <br /> to 7,100 µg/L TPHg, and 2,900 µg/L to 800 µg/L benzene respectively <br /> The most recent groundwater monitoring results for the site, from fourth quarter 2000, <br /> reported groundwater levels approximately 20 to 21 feet bgs calculated to flow east to <br /> northeast under a hydraulic gradient of 0 007 feet/foot <br /> 2 <br />