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10 November 1999, AGE-NC.Project No. 98-0433 ' . Page 11 of l3 ' Ground Woter Ifonitoring ff'ells • TPH g was detected in five of the monitoring well samples collected from tllc site at concentrations ranging from 58 dig/l to 5,000 4g11 (MW-1). TPH-d was detected in six of the well samples analyzed at concentrations ranging from 55 �zg/l to 24,000 pg/l (MW-2). t Benzene was detected in one of the ground water well samples. Well M WA near tlle•former ; UST excavation contained benzene at a concentration of.690 ug/l. Other volatile organic compounds were detected at concentrations up to 570 µg11 (xylene). y • iti1TBL ,vas detected in three of the water samples analyzed by EPA method 5020 and four of the samples analyzed by 17-IIA method 8260. MTBE was detected in wells 1`4W-1, NI W-2, ' MW-3 and MW-4 at concentrations ranging from 1.1 pg/l to 3;300 r. ()1I (FPA 8260) DiM.'. was also detected in one of the water samples analyzed at a concenlratlons of 4,l,u.g/l (MW- F)gure MW-Figure 4 depicts an approximate areal distribution of ground water containing TPI-I-g, TPII-d, benzene and.M"I-131-?. Analytical results frons ground water samples are summarized in `fable 4. The laboratory report (MAJ Lab ID Numbers" 17999 through 18010),QAIQC and chain-of-custody are Mcluded In Appendix G. ' 4.5. GROUND WATER 1311EVAfION; FLOW DIRFICTION AND GIZAIOIE�N'r A California state-licensed survey engineer from 13aumbach & Piazza Inc, surveyed a refcrenec point ' os1 the top of each ground water monitoring well casing at the site to the nearest 0.01-foot rclativc to the San Joaquin County Bench Mark Datum 9 131\431•4-37. -Flie results of file nionitoring well survey are contained in Table 3. The surveying report (Bawribach & Piazza) is presented in ' Appendix H. Depth to ground tivatcr at the site ranged from 16.95 to 18.70 meet below,well casing top. The ground , ' water elevation in each well`were calculated from these data. 'Flie ground w atcr clevations at the site , ringed fron140.13 feet to 40.27 feet above mean sea level (mss). ' 1"lie graimd }eater flow direction and gradient was calculated from the well elevation data. The ground water Clow was directed toward the slorth a-way from the former UST arca, llovvever the ' ground water flow��.direction appear to be directed wvest toward truck €wvash -ons wvell M'� -6 and (MW-7. Figure 5 illustrates the contoured ground water elevations as measured on 29 August 1999. fivaneed G'mEnvironnien(it I,lite.