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24 November 1997 <br /> AGE-NC Project No 95-0104 <br /> Page 3 of 4 <br /> micrograms per liter) <br /> BTEX compounds were detected in ground water samples collected from wells NIW-1, MW-5, MW- <br /> 6 and VW-1 Benzene was detected m these wells at concentrations as high as 110 ppb, toluene was <br /> detected at concentrations as high as 1,400 ppb, ethylbenzene was detected at concentrations up to <br /> 290 ppb,xylenes were detected at concentrations as high as 1,800 ppb MTBE was not detected in <br /> any of the samples by EPA Method 8020 analyses <br /> MTBE was detected from VW-1 at a concentration of 1 1 ppb, TBA was detected from MW-6 and <br /> VW-1 at concentrations of 53 ppb and 31 ppb, respectively DIPE, TAME and ETBE were not <br /> detected in any ground water samples during this quarterly sampling event Analytical results of <br /> selected ground water samples are summarized in Table 2 - Analytical Results of Ground Water <br />' Samples The laboratory report (AAL Batch Number 97-1002-007) and chain-of-custody forms are <br /> presented in Appendix B <br />' 40N L <br /> CO C USIONS AND RECOMMENDATIONS <br /> 41 CONCLUSIONS <br />' Based upon data collected during this investigation, AGE concludes the following <br /> • In September 1997, the gradient was approximately 0 006 ft/ft (approximately 32 feet per <br /> mile) directed toward the north-northeast and south-southwest due to an apparent northwest <br /> to southeast oriented "ridge" of surface ground water elevation <br />' • The ground water elevation at the site continues to be above the slotted screened intervals in <br /> wells MW-2, MW-3 and MW-4 <br /> • Due to elevated concentrations of petroleum hydrocarbons detected in the sample from VW- <br /> 1, it appears that VW-1 is located near the center of the dissolved hydrocarbon plume <br /> • Concentrations of benzene detected in MW-1, MW-5 and VW-1 exceeded the State of <br />' California Maximum Contaminant Levels (MCLs)for drinking water of 1 0 µg11, respectively <br /> • Concentrations of toluene detected in VW-1 exceed the MCLS for drinking water of 150 ,ugll <br /> • Concentrations of xylene detected in VW-1 exceed the MCLs for drinking water of 1,750 <br /> µg11 <br />' Concentrations of MTBE detected in VW-1 during the June 1997 sampling event were below <br /> the Central Valley Regional Water Quality Control Board recommended 35 ppb closure limit <br /> • <br /> Advanced GcoEn�tronntental,Inc- <br /> I <br />