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1 Third Quarter 2004 Thrifty#172 October 13, 2004 ' Page 2 In a letter dated September 1, 2004, the San Joaquin County Environmental Health Department ' (SJCEHD) requested that Thrifty add 1,2-DCA, EDB, and soluble lead to the analyses of all wells Since the samples were analyzed by EPA Method 8260B, Thrifty was able to report 1,2- DCA and EDB, but due to the fact that sampling was previously conducted on August 11, 2004, ' soluble lead was not added for the third quarter 2004 event TPHg, BTEX, and MTBE concentrations appear in Table 1, while historical oxygenate and ' alcohol results are presented in Table 2 Copies of groundwater laboratory reports and cham-of- custody documents are included in Appendix B TPHg, benzene, and MTBE isoconcentration maps are presented as Figures 3, 4, and 5, respectively The highest concentrations of TPHg, 1 benzene, and MTBE in groundwater were found in monitoring well MW-11 (193,000 ug/L, 24,200 ug/L, and 941 ug/L, respectively) The remaining site wells have very low to non- detectable constituent concentrations During the current quarter, TPHg (959 ug/L),benzene (141 ug/L), and MTBE (344 ug/L) concentrations were detected m offs1te, upgradient well MW-9 for the first time since quarterly sampling was initiated in February 1996 EMC re-sampled wells MW-9 and MW-11 on September 30, 2004, to confirm the presence of dissolved hydrocarbon constituents in well MW- ' 9 and to confirm the decline in MTBE concentration ion well MW-11 The results of the September 30, 2004, confirm the reduction of MTBE concentration in well MW-11 and the presence of TPHg (394 ug/L),benzene (40 ug/L), and MTBE (156 ug/L) in well MW-9 The low ' to ND concentrations in the onsite well MW-10 located upgradient between the source and the offsite well MW-9, as well as the benzene + toluene/ ethylbenzene +xylenes ratio indicates that this is a recent release The source of the release is uncertain EMC field sampling forms for the ' September 30, 2004, sampling event are provided in Appendix A and laboratory reports are provided in Appendix B ' Since the third quarter of 1997, Thrifty has analyzed for oxygenates di-isopropyl ether(DIPE), ethyl-tert butyl ether (ETBE), tert-amyl methyl ether(TAME), and tert-butanol (TBA), and MTBE by method 8260B The alcohols (ethanol and methanol) were analyzed by ASTM ' standard D285 The SJCEHD requested these analyses Laboratory results indicate no alcohols or oxygenates (besides MTBE) were detected above the laboratory detection limit, with the exception of TAME (35 2 ug/L) and TBA (100 ug/L) in well MW-9 The detections limits for ' TAME and TBA were significantly elevated in well MW-11 It has been over three years without detecting the alcohol constituents in groundwater samples. Therefore, Thrifty respectfully repeats its request for cessation of the requirement for methanol and ethanol ' analysis at this site. ��