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13 December 1999 <br /> !_ AGE-NC Project No. 98-0433 <br /> Page 11 of 13 <br /> concentrations ranging from 58 �ig/l (MW-7)to 5,000 4g/1 (MW-1). TPH-d was detected'in <br />' six of the well samples analyzed at concentrations ranging from 55 4g1l (MW-5) to 24,000 <br /> 1,ig11 (MW-2). <br /> ' Benzene was detected in one of the ground water well samples. Well MW-1 near the former <br /> UST excavation contained benzene at a concentration of 690 ,ug/l. Other'volatile organic <br /> compounds were detected at concentrations up to 570,ug/1 (xylene)., <br /> • MTBE was detected in three of the water samples analyzed by EPA method 8020 and four <br /> of the samples analyzed by EPA method 8260. MTBE was detected in wells MW-1, MW-2, <br /> MW-3 and MW-4 at concentrations ranging from 1.1 µg11 to 3,306 Mcgli.(EPA 8260) DIPS. <br /> ' was also detected in one of the water samples analyzed at a concentrations of 4.1 kig/1•(MW- <br /> 8). <br /> Figure 4 depicts an approximate areal distribution of impacted ground water containing TPH-g,. <br /> TPH-d, benzene and MTBE. <br /> Analytical results from ground water samples are summarized.in Table 5. The laboratory report <br /> (MAI Lab ID Numbers 17999 through 18010),QA /QC and chain-of-custody are included in <br /> Appendix G. <br /> ' 4.5. GROUND WATER ELEVATION, FLOW DIRECTION AND GRADIENT <br /> A California state-licensed survey engineer from Baumbach&Piazza Inc. surveyed a reference point <br /> on the top of each ground water monitoring well casing at the site to the nearest 0.01.-foot relative <br /> to the San Joaquin County Bench Mark Datum 4 BM3M-37. The results of the monitoring,well <br /> survey are contained in Table 6. The surveying report (Baumbach & Piazza)-. is presented in <br /> ' Appendix H. - <br /> Depth to ground water at the site ranged from 16.95 to 18.70 feet below well casing top. The ground <br /> water elevation in each well were calculated from these data. The ground water elevations at the site <br /> ranged from 40.13 feet to 40.27 feet above mean sea level (msl). <br /> ' The groundwater flow direction and gradient were calculated from the well elevation data. The <br /> ground'water flow was directed toward the northwest away from the former UST area, however the <br /> ground water flow direction appear to be' directed, somewhat southwest toward the truck wash area from well MW-6 and MW-7. Figure 5 illustrates te contoured ground water elevations as measured <br /> on 29 August 1999. <br /> Advanced GeoEnvironmental,Inc. <br /> t <br />