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. are included as Appendix B An isoconcentration contour map of methyl- tertiary butyl ether (MTBE) concentrations is presented as Figure 3 4.0 CONCLUSIONS • The groundwater sample collected from monitoring well MW- 1 contained 42 ppb MTBE • The groundwater samples collected from monitoring well MW-2 contained 14 ppb benzene, 39 ppb ethyl benzene, 21 ppb total xylenes, 120 ppb MTBE, 05 ppb tert-amyl methyl ether (TAME), 62 ppb t e r t- butanol (TBA), and 150 ppb TPH-G • The groundwater samples collected from monitoring well MW-4 contained 54 ppb MTBE • The groundwater samples collected from monitoring well MW-5 contained 52 ppb MTBE • No other hydrocarbons were detected above the laboratory method reporting limits in any of the groundwater samples collected The benzene and MTBE concentrations in the groundwater sample collected from monitoring well MW-2 exceeded the California Department of Health Services (DHS) Maximum Contaminant Levels (MCLs) for drinking water No other compound concentrations exceeded MCLs Hydrocarbon concentrations decreased slightly in monitoring wells MW-1 and MW-2, and the MTBE concentration in MW-1 reached an historic low for the third consecutive quarter The MTBE concentrations in monitoring wells MW-4 and MW-5 increased slightly, while the TBA concentration in MW-5 fell below the laboratory method reporting limit for the first time since monitoring began 5.0 RECOMMENDATIONS ASE recommends continuing operation of the ozone sparging system a n d quarterly groundwater monitoring The next sampling is scheduled for January 2005 Singh's Unocal Service Station Quarterly Report — October 2004 Sampling -3-