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. Four, Five, and Six. The certified analytical report and chain-of-custody documentation 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 110 ppb TPH-G, 5.1 ppb tert-butanol (TBA) and 4 9 ppb MTBE. • The groundwater sample collected from monitoring well MW-2 contained 100 ppb TPH-G, 640 ppb MTBE, 150 ppb TBA, and 3 9 ppb TAME. • The groundwater sample collected from monitoring well MW-3 contained no detectable concentrations of all compounds tested • The groundwater sample collected from monitoring well MW-4 contained 20 ppb MTBE and 1.3 ppb TAME • The groundwater samples collected from monitoring well MW-5 contained 3.2 ppb MTBE and 8.1 ppb TBA. • The groundwater sample collected from monitoring well MW-6 contained no detectable concentrations of all compounds tested • No other hydrocarbons were detected above the laboratory method reporting limits in any of the groundwater samples collected. The MTBE concentration in the groundwater sample collected from monitoring wells MW-2 and MW-4 exceeded the California Department of Health Services (DHS) Maximum Contaminant Levels (MCLS) for drinking water. No other compound concentrations exceeded MCLs Hydrocarbon and oxygenate concentrations were generally consistent with the previous quarter's concentrations. 5.0 RECOMMENDATIONS ASE recommends continuing operation of the ozone sparging system and , quarterly groundwater monitoring The next sampling is scheduled for October 2005 Singh's Unocal Service Station Quarterly Report - August 2005 Sampling -3-