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1 <br /> 1 <br /> documentation are included as Appendix B. An isoconcentration contour <br /> map of methyl-tertiary butyl ether (MTBE) concentrations is presented as <br /> ' Figure 3 <br /> r <br /> ' 4.0 CONCLUSIONS <br /> • The groundwater sample collected from monitoring well MW-1 <br /> ' contained 140 ppb TPH-G and 4.3 ppb MTBE. <br /> • The groundwater sample collected from monitoring well MW-2 <br /> contained 410 ppb TPH-G, 460 ppb MTBE, 91 ppb tert-butanol (TBA), <br /> ' 2.6 ppb TAME, 2.2 ppb benzene, and 0.68 ppb ethylbenzene. <br /> • The groundwater sample collected from monitoring well MW-4 <br /> contained 97 ppb TPH-G, 18 ppb MTBE, and 1.7 ppb TAME. <br /> • The groundwater samples collected from monitoring well MW-5 <br /> contained 120 ppb TPH-G, 10 ppb MTBE, and 25 ppb TBA. <br /> ' No other hydrocarbons were detected above the laboratory method <br /> reporting limits in any of the groundwater samples collected. <br /> The MTBE concentration in the groundwater sample collected from <br /> monitoring wells MW-2 and MW-4 exceeded the California Department of <br /> Health Services (DHS) Maximum Contaminant Levels (MCLs) for drinking <br /> • water. The benzene concentration in the groundwater sample collected <br /> from monitoring well MW-2 slightly exceeded the DHS MCL for drinking <br /> ' water. No other compound concentrations exceeded MCLs. Hydrocarbon <br /> and oxygenate concentrations generally increased in all monitoring wells <br /> sampled this quarter. <br /> ' 5.0 RECOMMENDATIONS <br /> ASE recommends continuing operation of the ozone spargnng system and <br /> quarterly groundwater monitoring. The next sampling is scheduled for <br /> July 2005. <br /> Singh's Unocal Service Station Quarterly Report - April 2005 Sampling <br /> ,' -3- <br />