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1 <br />' 20061 `Quarter Groundwater Report <br /> • Frontier Transportation, Inc. <br />' April 28, 2006 <br /> Page 3 <br />' 10' bgs in MW-15 using EPA Method 8260B No other oxygenates or lead scavengers were <br /> detected The maximum TPH-gas detected was 1 7 mg/kg at 10' bgs in MW-15 using EPA <br />' Method 8015M No detectable BTEX was identified in the soil column for MW-15 through <br /> MW-18 See Figure 2 for well locations <br />' In August 2005, BEA installed three shallow groundwater wells Monitoring wells MW- 1 ,� <br /> 19, MW-20 and MW-21 were advanced to 20' bgs and screened from 5' bgs to 20' bgs See <br /> Figure 2 for well locations <br /> 3.0) SITE GEOLOGYIHYDROGEOLOGY <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 Holocene <br /> age which overlay sedimentary rocks of Cretaceous to Tertiary age These sedimentary units, in <br /> turn, overlay a crystalline basement of Paleozoic and Mesozoic metamorphic and igneous rocks <br />' • The shallow subsurface geology in the site vicinity is a heterogeneous mix of gravel, sand, silt, and <br /> clay(Reference Site Characterization,Report, Twining Laboratories, October 16, 1996) BEH <br /> encountered predommantly clays with traces of interbedded sands from 0' to 25' bgs during well <br />' advancement in January of 1998 <br /> 8S � r J <br /> Fust subsurface water was encountered at depths from 1T to 1-2' 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 The groundwater flow is generally <br /> a western direction beneath the site (See Figure 3, Groundwater Gradient Map) Historic first <br /> subsurface groundwater data identified a west or southwest flow beneath the site Groundwater <br /> was also encountered at approxirnately�5' bgs during installation of deep monitoring wells MW- <br /> 12 through MW-16 and MW-18 The potentiometric groundwater levels in these deep wells, <br /> however, were similar to the first 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 wmter and yearly high in the spring <br /> I <br /> i <br /> I <br />