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I ' 2004 1" Quarter Groundwater Report • Frontier Transportation ' May 20, 2004 Page 3 within the west-central portion of the Great Valley Geomorphic province of California The Great Valley has been filled with a sequence of older to younger alluvium of Pliocene to Holocene age which overlay sedimentary rocks of Cretaceous to Tertiary age These sedimentary ' units, in tum, overlay a crystalline basement of Paleozoic and Mesozoic metamorphic and igneous rocks The shallow subsurface geology in the site vicinity is a heterogeneous mix of gravel, sand, silt, and clay(Reference Site Characterization Report, Twining Laboratories, October 16, 1996) BEII encountered predominantly clays with traces of interbedded sands from 0' to 25' bgs during well advancement in January of 1998 FB,Sr 3r First subsurface water was encountered at depths fromXl' to '"bgs during tank removal and monitoring well installation at this site in 1995 and 1996 Since then, first subsurface water has been encountered beneath the site between 6' and 10'bgs Data collected in March of 2004 identified the flow of groundwater in a generally western direction beneath the site (See Figure 3, Groundwater Gradient Map) Historic first subsurface groundwater data identified a wet or southwest flow beneath the site Groundwater was also encountered at approximately�9' bgs ' during installation of deep monitoring wells MW-12 through MW-16 and MW-18 The potentiometnc groundwater levels in these deep wells, however, were similar to the first subsurface water levels ' • Hydrographs are presented as Figures 4 and 5 for shallow groundwater monitoring wells i (up to 25-feet bgs) and deep groundwater monitoring wells (40-feet bgs) Groundwater levels beneath the site appear to be affected by seasonal recharge In general, the groundwater is at its yearly low in the winter and yearly high in the spring ' 4.0) QUARTERLY GROUNDWATER SAMPLE RESULTS ' BEH contracted Del-Tech to collect groundwater samples from monitoring wells MW-1 through MW-18 on March 24, 2004 for laboratory analysis Groundwater parameters (pH, temperature, and conductivity) were measured before, during, and after well purging (See ' Appendix A for Monitoring Well Field Logs) Groundwater samples were analyzed for TPH-d, TPH-g, TPH-m and BTEX using EPA methods 8015 modified for diesel, 8015 modified for gasoline, 8015 modified for motor oil and 8020 for BTEX, respectively In addition, groundwater samples were analyzed for MTBE, tertiary butyl alcohol (TBA), di-isopropyl ether (DIPS), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME), 1,2-dichloroethane (1,2-DCA) and 1,2-dibromoethane (EDB) using EPA method 8260 Laboratory analysis results for all monitoring episodes are presented in Table 1 Recent laboratory analytical reports are included as Appendix B ' Historical groundwater data has identified dissolved TPH-m in monitoring well MW-3 • 1