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1 17 April 2000 AGE-NC Project No. 95-0100 ' Page 6 of 6 .' 3.4. GROUND WATER ELEVATION, FLOW DIRECTION AND GRADIENT A California state-licensed survey engineer from Baumbach&Piazza Inc. surveyed a reference point ' on the top of each ground water monitoring well casing at the site to the nearest 0.01-foot relative to the San Joaquin County Bench Mark Datum # BM3M-37. The results of the monitoring well survey are contained in Table 3. The surveying report (Baumbach & Piazza) is presented in ' Appendix C. Depth to ground water at the site ranged from 42.35 to 43.68 feet below well casing tops on the two ' occasions that depth to water was measured. The ground water elevation in each well were calculated from these data. The ground water elevations at the site ranged from 72.00 feet to 74.11 feet above mean sea level (msl). The ground water flow direction and gradient were calculated from the well ' elevation data collected on two separate occasions. Contours of the ground water elevation data suggest that the ground water flow was directed toward ' the north away from the former on area, shifting in the down-gradient direction toward the northwest. Ground water gradient was calculated to be 0.06 away the former UST area. Figure 3 lie illustrates the contoured ground water elevations as measured on various dates. ' 3.5. DOMESTIC WELL SAMPLE ANALYSIS ' A water sample was collected from two of the domestic drinking water wells on the site (well 1 and well 2). The well pump was operated for one minute. A sample was collected from the dedicated sample tap on the well head; the sample was collected in three 40-m1 EPA-approved volatile organic ' analysis (VOA) vials. The sample was stored in a chilled container and transported under chain-of-custody to a DHS- certified laboratory. The sample was analyzed for constituents listed in Section 2.6. Petroleum hydrocarbons and fuel oxygenates were not detected above the reporting limits in the ' sample collected From the domestic wells on the site (Appendix F). _ 4.0.,=._SUMMARY„AND.CONCLUSIONS_.._:— The following conclusions were drawn from the results of this investigation: • The ground water flow direction inferred from measurements taken on two occasions at the site is generally northward. • MTBE was detected in one well on the site at a concentration of 97 4gll by Method 8260 ' Advanced Geol nvironmental,Inc.