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07 December 1998 AGE-NC Project No 95-0105 Page 3 of 5 ' 3 1 GROUND WATER GRADIENT AND FLOW DIRECTION The elevation of ground water in each well was calculated by subtracting the ground water depth from the surveyed casing elevation(Table 1) The casing elevation of each well had been previously surveyed relative to a City of Tracy bench mark Ground water elevations at the site ranged from ' 23 14 to 2199 feet above mean sea level Between January and June 1998, ground water elevation decreased an average of 0 33 feet at the site ' The ground water flow direction in June 1998 was directed generally toward the northwest on the southern portion of the site and Is southwesterly towards well MW-4 from well MW-6 located across Grant Line Road The flow direction observed(depression at well MW-4)may be due to a differing ' well depth construction and llthology amongst the wells The total depth of well MW-4 was nine feet bsg,while the other wells are completed to depths of 14 to 26 feet bsg MW-4 is completed primarily ' in shallow silt and clay, while the deeper completion depths of MW-1, MW-2 and MW-3 are screened across sand intervals Ground water level may lag in MW-4 due to the lower permeability of the fine-grained soil Figure 3 depicts the ground water elevation contours at the site 1• 3 2 PETROLEUM HYDROCARBON-IMPACTED GROUND WATER None of the analytes of interest were detected in the ground water samples collected from wells MW-1,MW-2,MW-5 and MW-6,all or some of the analytes of interest were detected in the ground ' water sample collected from MW-4 and MW-3 j I TPH-g and TPH-d were detected in monitoring well MW-4 at concentrations of 10,000 parts per ' billion (ppb, reported as micrograms per Inter) and 1,900 ppb, respectively Benzene, toluene, ethylbenzene and xylenes were detected to monitoring well MW4 at concentrations of 270 ppb, 840 ppb, 660 ppb and 1,800 ppb, respectively TPH-g was detected in well MW-3 at a concentration of ' 65 ppb, benzene and total xylenes were also detected at concentrations of 8 2 ppb and 0 61 ppb, respectively ' Oxygenated volatile organics were not detected in any of the samples analyzed by EPA Method 8260m ' The analytical results for the ground water samples are summarized in Table 2 and Table 3 The laboratory report (MAI Sample Nos 90067 to 90072), quality assurance and quality control data ' (QA/QC) and chain-of-custody form are included in Appendix B ' Advanced GeoEnvtronmental,Inc j I i