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• Two dissolved-phase oxygenate constituents (MTBE and 1,2-DCA) have been detected in the groundwater MTBE concentrations were detected in monitoring wells MW-3, 3A, 313, 11, and 13 MTBE concentrations appear to be increasing in monitoring wells MW-3A, 313, and 11 and fluctuating in monitoring wells MW-3 and MW-13 Concentrations of 1,2-DCA have only been detected in monitoring well MW-11, which is located off-site, directly south of monitoring well MW-3 This constituent has not been detected in wells located in the UST release area or immediately dawn-gradient of the release area and may not be related to the release at the Canteen Facility site Concentrations of dissolved-phase hydrocarbons in the groundwater exceed the CAMCLs for benzene, tolueyne etthylbenzene, xylenes, MTBE, and 1,2-DCA TPH-G concentrations have vaned from< 50 to 140,000 4g/]L The majority of the groundwater impacts are centered in and around the MW-3 and MW-13 series wells Concentrations of 1,2-DCA detected in off-site monitoring well MW-11 have exceeded that constituents CAMCL, however, these concentrations do not appear to be related to the UST release Historical groundwater sampling has been conducted at the site since 1995 The last two years of monitoring data indicated the following maximum hydrocarbon concentrations for the various • constituents I CA Dox Maximum MCLs Concentration Sample Sample Constituent (Ag/L) (µg/L) Location Date Benzene 10 27,000 MW-13 05/10/01 Toluene 150 42,000 MW-13 05/10/01 3 Ethylbenzene 700 4,400 MW-13 08/01/02 Xylenes 1,750 25,000 MW-13 05/10/01 MTBE 13 1,900 MW-13 05/10/01 TPH --- 220,000 MW-13 I 05/10/01 1,2-DCA 050 51 MW-11 10/31/02 A complete summary of historical groundwater analytical data is provided in Table 3 Isoconcentration maps showing the horizontal extent of the dissolved-phase hydrocarbons are presented in Appendix B E. REGIONAL WATER USE Water Well Information Il-3