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30 October 1996 AGE-NC Project No. 95-0105 Page 2 of 4 6w 2.2. COLLECTION OF GROUND WATER SAMPLES Water samples were collected from each well using a new disposable plastic bailer. Each water sample was collected in two 40-nil VOA vials and one 1-liter amber bottle. After collection, the samples were properly labeled, placed in a chilled container and transported under chain-of-custody to MAI laboratory. Each sample was analyzed for total petroleum hydrocarbons quantified as gasoline and as diesel (TPH-g and TPH-d), and for volatile aromatic compounds (benzene, toluene, ethyl-benzene and total xylene: BTE&X) with methyl-tert-butyl ether: MTBE) in accordance with EPA methods 5030/8015m, 5030/8015m and 602, respectively. 3.0. FINDINGS `W 3.1. GROUND WATER GRADIENT AND FLOW DIRECTION The relative elevation of ground water in each well was calculated by subtracting the ground water depth from the surveyed casing elevation(Table 1). The casing elevations of each well was surveyed relative to a City of Tracy bench mark. Ground water elevations at the site ranged from 21.04 feet in MW-6 to 21.65 feet in MW-1. Between May and August 1996, ground water elevation decreased an average of 1.i feet at the site. The ground water gradient appears to follow the regional and documented historic gradient to the north. �.,. 3.2. PETROLEUM HYDROCARBON-IMPACTED GROUND WATER TPH-g was only detected in monitoring well MW-4, at a concentration of 13,000 micrograms per +� liter(µg/l, approximately equivalent to parts per billion, ppb). Benzene, toluene, ethyl benzene and xylenes were detected in well MW-4 at concentrations of 88 ppb, 250 ppb, 570 and 1,900 ppb, respectively. Benzene was also detected in the sample from well MW-3 at a concentration of 1.4 ppb. MTBE was only detected in well MW-4 at 59 ppb;the analyte was confirmed by GCMS. TPH- , d was detected in wells MW-1, MW-2, MW-3, MW-4 and MW-5 at concentrations of 83, 96, 120, 4,900 and 120 ppb, respectively. Petroleum hydrocarbons were'not detected in the sample collected from the down gradient well MW-6. The analytical results for the ground water samples are summarized in Table 2. The laboratory report(MAI Laboratory Nos. 68712 to 68717) and chain-of- custody are included in Appendix B. +r.