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i MWnIMLY GRIXINUWATER"Mr111111NG REPOU 6131 PaCMC Avenue Stockton CalUorft Groundwater elevations decreased 0 28 foot, 0 26 foot, and 0 16 foot in wells MW-1, IMW-2, and MW-3, respectively, from July to October A groundwater elevation hydrograph is included as Figure 3 On the basis of the October 8, 1991, measurements, the estimated direction of groundwater flow was to the east at an average gradient of 0 001 ft/ft (0 10 percent) Figure 4 is a potentiometric surface map of the shallow water- bearing zone for October 8, 1991 4.2 Groundwater Sampling and Analysis Groundwater samples from monitoring wells MW-1 and MW-2 were collected on October 8, 1991, and delivered under chain-of-custody to NET Pacific, Inc , of Santa Rosa, California, and Eureka Laboratories, Inc , of Sacramento, California, both state- certified analytical laboratories All samples were collected according to the SOP included in Appendix A Monitoring well sampling information is included in Appendix B Well MW-3 was not sampled due to the presence of floating hydrocarbons The samples were analyzed for a) TPH, as gasoline, by GC/FID Method 5030, b) benzene, toluene, ethylbenzene, and total xylenes (BTEX) by EPA Method 602, and c) total and fecal coliform by MMO/MUG The groundwater analytical results are summarized in Table 2 The analytical reports and chain-of-custody forms are included in Appendix C Concentrations of TPH and benzene, reported in Table 2, are also shown on Figure 5 Analysis of samples collected from well MW-1 in October indicated concentrations of 0 16 and 0 0016 ppm for TPH, as gasoline, and benzene, respectively The laboratory reported that the positive response for TPH, as gasoline, was due to the presence of an unknown hydrocarbon, not gasoline Other BTEX compounds were not indicated above i detection limits in MW-1 For MW-2, TPH, as gasoline, was indicated at 10 0 ppm, and analysis for BTEX indicated concentrations ranging from 0.26 (ethylbenzene) to 7 6 ppm (benzene) Both total and fecal coliform were reported at 9 20 MPN in MW-1, and 12.0 iMPN in MW-2 I 1 I i i9"20E RFr -3- i