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i ' 2005 1"Quarter Groundwater Report • Frontier Transportation April 28, 2005 Page 3 3.0) SITE GEOLOGY/HYDROGEOLOGY IThe site is located on the boundary of the Sacramento Valley and the San Joaquin Valley within the west-central portion of the Great Valley Geomorphic province of California The IGreat 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 turn, 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 Resort, 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 M-2 ��aa" First subsurface water was encountered at depths from lYto 1z' 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 2005 ' identified the flow of groundwater bearing N25°W in the northwestern corner, S60°W along the south and N15°E along the eastern side of the site The groundwater flow is generally a western direction beneath the site (See Figure 3, Groundwater Gradient Map) Historic first subsurface ' groundwater data identified a vest or southwest flow beneath the site Groundwater was also encountered at approximately335' bgs during installation of deep monitoring wells MW-12 through MW-16 and MW-18 The potentiometric groundwater levels to 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 (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 This spring the water levels seemed to be lower than expected, which could be the result of a dry summer season in 2004 ' 4.0) QUARTERLY GROUNDWATER SAMPLE RESULTS BEA contracted Del-Tech to collect groundwater samples from 9 of the monitoring wells ' at the site on March 16, 2005 for laboratory analysis Monitoring wells sampled were MW-1, MW-3R, MW-9, and MW-13 through MW-18 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-g and BTEX using EPA methods 8015 and r8020 and for MTBE, tertiary butyl alcohol (TBA), di-isopropyl ether (DIPE), ethyl tertiary butyl