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SECTION 3.0 SUMMARY OF PREVIOUS INVESTIGATIONS <br /> mg/L, 8,100 ptg/L, 5,600 µg/L, 290 µg/L, 6,500 pg/L, and 60 µg/L, respectively by EPA <br /> Method 8020 The maximum BTEX concentration was detected in a groundwater sample <br /> collected from well MW-1 on July 2, 1996 In the groundwater sample collected from well <br /> MW-1, TPH-g, TPH-d, BTEX, and MTBE concentrations were detected at concentrations of <br /> 51 mg/L, 2 6 mg/L, 10,100 pg/L, 7,200 µg/L, 1,100 �Lg/L, 6,600 µg/L, and 38 µg/L, <br /> respectively Graphic depictions of historical groundwater concentrations of contaminants <br /> versus time are presented in Figure 5-7 <br /> • Based on the review of Ninyo & Moore's Third Quarter 1999 groundwater data and report <br /> (Ninyo & Moore, 1999), groundwater elevations have decreased more than 2 feet since June <br /> 1999 The maximum TPH-g, BTEX, and MTBE concentrations were detected at well VW-2 <br /> as follows 4,300 gg/L, 1,270 pg/L, 98 µg/L, 399 pg/L, 869 pg/L, and 32 pg/L, respectively <br /> In summary, 12 groundwater monitoring wells and two vapor monitoring wells were installed at <br /> the Stockton Yard site between 1992 and 1996 The groundwater and vapor monitoring wells are <br /> located onsite and are included in the current groundwater monitoring program, including routine <br /> groundwater monitoring and analysis for TPH-g and TPH-d using EPA Method 8015 modified, <br /> BTEX using EPA Method 8020, and MTBE using EPA Method 8260 None of the groundwater <br /> momtonng wells have been abandoned at the Stockton Yard site <br /> URS Greiner Woodward ClydeS 1FROJ441040f00041SYY4RDIMAINTYAROSA.DOC j-, <br />