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+' 4.0 CONCLUSIONS The groundwater samples collected from monitoring well MW-1 contained 14 parts per billion (ppb) methyl-tertiary-butyl ether (MTBE). The groundwater samples collected from monitoring well MW-2 contained 7,600 ppb TPH-G, 390 ppb benzene, 360 ppb toluene, 340 ppb ethyl benzene, 1,100 ppb total xylenes, 3,700 ppb MTBE, 14 ppb tert-amyl- methyl-ether (TAME), and 370 ppb tert-butonal (TBA). Groundwater samples collected from monitoring well MW-4 contained 290 ppb TPH-G, 25 ppb benzene, 540 ppb MTBE, and 25 ppb TAME. Groundwater samples collected from monitoring well MW-5 contained 130 ppb TPH-G, 14 p p b MTBE and 10 ppb TBA. No other hydrocarbons were detected above laboratory reporting limits in any of the groundwater samples collected. There appears to be a decreasing trend in hydrocarbon and oxygenate concentrations detected in the groundwater samples collected from monitoring wells MW-1 and MW-5. Concentrations of all compounds detected in groundwater samples collected from all other monitoring wells are consistent with previous results. All the compounds analyzed in monitoring wells MW-3 and MW-6 were below laboratory detection limits. The only compound detected in monitoring well MW-1 was MTBE. 5.0 RECOMMENDATIONS ASE recommends the subject site remain on a quarterly sampling schedule. The next scheduled sampling is scheduled for July 2002. ASE is currently scheduling the work outlined in the Remedial Action Plan (RAP) dated March 26, 2002 which will be performed during the next quarter. 6.0 REPORT LIMITATIONS The results presented in this report represent the conditions at the time of the groundwater sampling, at the specific locations where the groundwater samples were collected, and for the specific parameters analyzed by the laboratory. It does not fully characterize the site for contamination resulting from sources other than the former underground storage tanks and associated plumbing at the site, or for parameters not analyzed by the laboratory. All of the laboratory work cited in this report was prepared under the direction of independent CAL-EPA certified laboratory. The independent laboratory is solely responsible for the contents and conclusions of the chemical analysis data. Singh's Unocal Service Station Quarterly Report - April 2002 Sampling -3-