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THIRD QUARTER,2002 GROUNDWATER MONITORING REPORT • USA STATION#110,STOCKTON SEPTEMBER 2002 3.1 Groundwater Flow and Gradient On July 29, 2002,groundwater data collected at the site indicated that depths to groundwater ranged from 60 11-feet below ground surface(bgs)in MW-1 to 61 20-feet bgs in MW-2P. The groundwater elevations ranged from-34.50-feet below mean sea level(MSL) in MW-1 to -35 55-feet below MSL in MW-2P Elevation data from MW-1 was not used because this well is constructed much shallower than the other wells on-site and GHH feels this may not be representative Groundwater elevation measurements indicate groundwater was flowing to the southeast at a hydraulic gradient of approximately 0 002-foot/foot Groundwater elevations and gradient are shown on Figure 4. A review of the historical field data suggests that the groundwater generally flows between southeast and northeast Historical groundwater elevation data can be found in Appendix C, it includes data before 1999 3.2 Groundwater Analytical Results For July 29,2002, all petroleum compounds were non-detect(ND) at the method detection limit m MW-1P, MW-5P,MW-6P and MW-2 TPH G was reported in samples from monitoring wells MW-2P and MW-1 at 780 micrograms per liter 14g11, and 780 µg11, respectively Benzene was detected in samples from MW-21?at 2.3 µg11. Toluene, ethyl-benzene, and xylenes were ND in all monitoring wells Using EPA Method 8260B,MTBE was reported in samples from MW-2P,MW-3P,and MW-1 at 200µg11,22,ug/l and 28µg/1,respectively DIPE was reported in samples from MW-1P, MW-2P, MW-3P, MW-51?and MW--6P at 57µg/1, 2 8µg11, 67 1.1g11, 190µg11 and 64µg11, respectively TBA was reported in samples from MW-2P,MW-3P, MW-5P, and MW-6P at 180 ug/l, 20 ug/l, 7.6 ug/l, and 7.6 ug/l,respectively. All other oxygenates were ND at the method detection limit for this sampling event 1,2-DCA was reported in samples from MW-1, MW-1P, MW-2P,MW-3P,MW-5P and MW-6P at concentrations ranging from 13 µg11 in MW-1 to 21 µg/1 inMW-5P The groundwater analytical results for this sampling event are summarized in Tables 2 and 3, and shown on Figures 5 and 6 A Copy of the laboratory report with COC documentation is included in Appendix B. Appendix D provides historical groundwater analytical data from before 1999 4.0 SCHEDULE The fourth quarter sampling event for 2002 will be conducted in October 2002 and the monitoring report will be submitted within 30 days of the end of the quarter 3