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are included as Appendix B An isoconcentration contour map of methyl- <br /> tertiary butyl ether (MTBE) concentrations is presented as Figure 3 <br /> 4.0 CONCLUSIONS <br /> • The groundwater sample collected from monitoring well MW- 1 <br /> contained 59 ppb MTBE <br /> • The groundwater samples collected from monitoring well MW-2 <br /> contained 39 ppb benzene, 076 ppb toluene, 12 ppb ethyl benzene, 29 <br /> ppb total xylenes, 280 ppb MTBE, 14 ppb tert-amyl methyl ether <br /> (TAME), 170 ppb tert-butanol (TBA), and 270 ppb TPH-G <br /> • The groundwater samples collected from monitoring well MW-4 <br /> contained 23 ppb MTBE <br /> • The groundwater samples collected from monitoring well MW-5 <br /> contained 49 ppb MTBE and 6 8 ppb TBA <br /> • No other hydrocarbons were detected above the laboratory method <br /> reporting limits in any of the groundwater samples collected <br /> The benzene and MTBE concentrations in the groundwater sample collected <br /> from monitoring well MW-2 exceeded the California Department of Health <br /> Services (DHS) Maximum Contaminant Levels (MCLs) for drinking water <br /> No other compound concentrations exceeded MCLs Hydrocarbon <br /> concentrations decreased slightly in monitoring wells MW-1, MW-4, MW-5, <br /> and MW-6, with MTBE concentrations in all of these wells reaching historic <br /> lows The TPH-G and ethylbenzene concentrations in monitoring well <br /> MW-2 decreased slightly, while the benzene, total xylenes, TAME, and TBA <br /> increased slightly <br /> 5.0 RECOMMENDATIONS <br /> ASE recommends continued quarterly groundwater monitoring The next <br /> sampling is scheduled for September 2004 <br /> Singh's Unocal Service Station Quarterly Report — July 2004 Sampling <br /> -3- <br />