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i 16 February 1999 AGE-NC Project No 97-0290 Page 9 of 11 4 3 GROUND WATER GRADIENT AND FLOW DIRECTION Ground water was encountered at a depth of approximately 47 feet bsg during the installation of MW-1 During the December 1998 monitoring, the depths to ground water ranged from 44 38 feet to 46 12 feet below the tops of the well casings The elevation of ground water in each well was calculated by subtracting the depth to ground water from the surveyed casing elevations Ground water elevations ranged from 2 36 to 2 80 feet above mean sea level(MSL) Depths-to-ground water during the January 1999 monitoring ranged from 43 36 feet to 45 28 feet Ground water elevations at the site ranged from 3 52 to 4 18 feet MSL Ground water rose approximately 1 5 feet between I04 December 1998 and 26 January 1999 Ground water data is summarized on Table 7 Ground water elevation contours based upon the data for the January 1999 monitoring event is Iillustrated on Figure 3 The ground water flow direction was south with a gradient of 0 0015 ft/ft Historical depth to ground water at the site has ranged from approximately 35 feet bsg in 1971 to 55 feet bsg in 1993 and 1996, based upon ground water reaps prepared by the San Joaquin County Flood Control and Water Conservation District between 1971 and 1996 44 ANALYTICAL RESULTS OF WATER SAMPLES TPH-g was detected at concentrations as high as 45,000 parts per billion (ppb, reported as micrograms per liter, MW-2) TPH-d was detected at concentrations as high as 4,900 ppb However, ' samples collected from MW-1 through MW-5 were not analyzed for TPH-d BTEX compounds were detected at concentrations as high as 5,000 ppb, 5,400 ppb, 1,200 ppb and 5,700 ppb, respectively (MW-2) Only toluene was detected in the samples collected from MW3 and MW5 at concentrations I of 12 ppb and 22 ppb, respectively TPH-d, the only analyte detected in the sample collected from B5, was present at a concentration of 100 ppb Petroleum hydrocarbons were not detected in the samples collected from MW6 and MW7 ' DIPE was detected in the samples collected from P2 and P3 at concentrations of 3 7 b and 7 1 b p pp pp I respectively Tertiary butanol was detected in the sample from P2 at a concentration of 23 ppb Oxygenated compounds were not detected in remaining samples collected from the site Analytical results of all water samples collected at the site are summarized on Tables 5 and 6 The laboratory report(MAI Sample Nos 96898-96899, 01889-01892, 99689-99693 and 02460-02461), chain-of- custody forms and QA/QC are included In Appendix D ' Advanced GeoEnsironmental,Inc