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I ' 22 May 1998 •` AGE-NC Project No 95-0128 ' Page 2 of 4 ' Samples were placed in a chilled container, under Ice and transported under chain-of-custody to McCampbell Analytical, Inc , (MAI) in Pacheco, Califonna Each sample was analyzed as follows ' • By EPA Method 8015 M for total petroleum hydrocarbons quantified as gasoline and diesel (TPH-g and TPH-d), ' • By EPA Method 8020 for volatile aromatic compounds(benzene,toluene,ethyl-benzene and total xylenes BTE&X) and • By EPA Method 8260m for oxygenated fuel additives methyl-tert-butyl ether (MTBE), ' tertiary butyl alcohol (TBA),di-isopropyl ether(DIPE),ethyl tertiary butyl ether(ETBE)and tertiary amyl methyl ether (TAME) 3.0. FINDINGS ' 3 1 GROUND WATER ELEVATION AND GRADIENT • The casing elevation of each well was surveyed relative to a City of Stockton bench mark of known elevation The elevation of ground water in each well was calculated by subtracting the ground water depth from the surveyed casing elevation The depth of ground water, casing elevations and ground ' elevations are tabulated in Table 1 The hydraulic gradient was Inferred by contouring the elevation of ground water in each properly screened well The ground water gradient and flow direction calculations were prepared from data collected from monitoring wells MW-4 through MW-7 and vapor well VW-1 The ground water gradient was calculated to be approximately 0 005 ft/ft directed north in the central western portion of the site and was also calculated to be approximately 0 007 ft/ft west on the north portion of the site The overall ground water flow direction is toward the northwest The ground water elevation contours for the site this quarter are illustrated in Figure 3 - Ground Water Elevation 32 CHEMICAL RESULTS OF GROUND WATER SAMPLES The highest concentrations of dissolved TPH were ere detected in the sample collected from vapor well VW-I TPH-g and TPH-d were detected at 51,000 parts per billion(ppb, reported as micrograms per liter) and 8,200 ppb, respectively The sample also contained BTE&X compounds at concentrations as high as 7,900 ppb (xylene) Benzene was detected at 4,000 ppb TPH-g and TPH-d were detected in monitoring wells MW-4 through MW-7 at concentrations as great as 3,900 ppb (TPH-g in MW-5, located near the northeast corner of the site) BTE&X Advanced GeoEnvlronmental Inc