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Atlantic Richfield Company Page 9 ARCO Station No 4932 Stockton Caltfomta August 29 2002 Laboratory analysis of groundwater samples from the newly installed wells detected TPHg, benzene, and ethylbenzene In one of the five samples at concentrations of 90 ug/L(DMW-3), 10 ug/L(DMW-2), and 0 62 ug/L(DMW-2), respectively Toluene was detected In four of the five samples collected at concentrations ranging from 13 ug/L(DMW-3) to 16 ug/L (DMW-2) Total xylenes were detected In four samples at a concentration ranging from 0 52 ug/I,(MW-10) to 0 81 ug/L (MW-11) MtBE was detected in four of the five samples at concentrations ranging from 8 5 ug/L(DMW-2) to 65,000 ug/L (EW-2) Other analytes were not detected above laboratory units Groundwater analytical data is presented In Table 2 and shown on Figure 6 Field and laboratory procedures are presented as Appendix H Well development and groundwater sampling parameters are included on the field sheets in Appendix I The groundwater monitoring wells were surveyed relative to mean sea level by Morrow Surveying, a licensed surveyor Attachment r contains the surveyor's site plan showing the locations and elevations of the wells 3.1.4.1 Groundwater Flow Direction Depth to groundwater at the site ranged from 28 '/2 feet bgs to 301/4 feet bgs and the groundwater flow In the shallow water bearing zone was to the northeast at an approximate gradient of 0 002 ft/ft and In the deep water bearing zone the direction was east-northeast also at a gradient of 0 002 ft/ft The groundwater gradhent and flow direction is presented in Table 3 and groundwater elevation contour maps are included as Figures 4 and 5 3.1.5 Stockpiled Soil and Rinsate Water A total of ten cubic yards of soil were generated during the installation MW-10, MW-11, DMW-2,DMW-3, and EX-2 One composite sample (4 sleeves to 1 sample)was collected from the stockpiled soil and analyzed for TPHg and BTEX by the DHS/LUFT method and total lead by EPA Method 6010B MtBE was detected In the stockpiled soil at a concentration of 0 32 ug/L Other analytes analyzed for were reported as nondetect Analytical data for the stockpiled soil composite sample is included in Table 7 The residual soil was transported by Dillard Trucking, Inc (Dillard) and disposed at Altamont Landfill in Livermore, California A total of three 55-gallon DOT drums of nnsate water were generated during dnlling activities Rinsate water was transported by Dillard Environmental along with water extracted during interim remediation to InStrat In Rio Vista, California, for disposal 3.1.6 Summary of Findings • Soils encountered during the drilling of DMW-2, DMW-3, and EW-2 consisted of clayey silt and silty clay from ground surface to approximately 10 feet bgs and Msilty sand to sand encountered from 10 feet bgs to the total depth of EW-2 (44 feet bgs) The deeper soils encountered in DMW-2 and DMW-3 consisted of silty 1\ARC0149321PAR1PAR doc