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• 2004 Yd Quarter Groundwater Report <br />' Frontier Transportation <br /> January 10,2005 <br /> Page 3 <br /> 3.0) SITE GEOLOGYMIYDROGEOLOGY <br /> The site is located on the boundary of the Sacramento Valley and the San Joaquin Valley <br />' within the west-central portion of the Great Valley Geomorphic province of California- The <br /> Great Valley has been filled with a sequence of older to younger alluvium of Pliocene to <br /> Holocene age which overlay sedimentary rocks of Cretaceous to Tertiary age These sedunentary <br /> units, in turn, overlay a crystalline basement of Paleozoic and Mesozoic metamorphic and <br /> igneous rocks. The shallow subsurface geology in the site vicinity is a heterogeneous mix of <br /> gravel, sand, silt, and clay (Reference Site Characterization Report, Twining Laboratories, <br /> October 16, 1996) BEH encountered predominantly clays with traces of interbedded sands from <br /> 0' to 25' bgs during well advancement in January of 1998 <br /> 5 I31 r�s/po <br /> First subsurface water was encountered at depths from kY`to k`bgs during tank removal <br /> and monitoring well installation at this site in 1995 and 1996 Since then, first subsurface water <br /> has been encountered beneath the site between 6' and 10' bgs Data collected in September of <br /> 2004 identified the flow of groundwater in a western direction beneath the site (See Figure 3, <br /> Groundwater Gradient Map) Historic first subsurface groundwater data identified a vySqt or <br /> southwest flow beneath the site Groundwater was also encountered at approximately"35' bgs <br /> 10 during installation of deep monitoring wells MW-12 through MW-16 and MW-18. The <br /> potentiometnc groundwater levels in these deep wells, however,were similar to the first <br /> subsurface water levels <br /> Hydrographs are presented as Figures 4 and 5 for shallow groundwater monitoring wells <br />' (up to 25-feet bgs) and deep groundwater monitoring wells (40-feet bgs). Groundwater levels <br /> beneath the site appear to be affected by seasonal recharge In general, the groundwater is at its <br /> yearly low in the winter and yearly high in the spnng <br />' 4.0 QUARTERLY GROUNDWATER SAMPLE RESULTS <br />' BEII contracted Del-Tech to collect groundwater samples from monitoring wells MW-1 it 3 R,9, <br /> -thFeugh-MW--Aon September 30, 2004 for laboratory analysis Groundwater parameters (pH, <br />' temperature, and conductivity)were measured before, during, and after well purging (See <br /> Appendix A for Monitoring Well Field Logs) Groundwater samples were analyzed for T �i <br /> TPH-g, T -m and BTEX using EPA methods , 8015 modified for ) 1 <br /> gasoline, 8 and 8020 for BTEX, respectively In addition, E <br />' groundwater samples were analyzed for MTBE, tertiary butyl alcohol (TBA), di-isopropyl ether <br /> (RIPE), ethyl tertiary butyl ether(ETBE),tertiary amyl methyl ether (TAME), 1, <br /> (4;2=D" anusing EPA method 8260 Laboratory analysis results <br /> for all monitoring episodes are presented in Table 1 Recent laboratory analytical reports are <br /> 0 <br /> I <br />