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I ' "d 20062 Quarter Groundwater Report ' Frontier Transportation, Inc. August 2,2006 Page 3 10' bgs in MW-15 using EPA Method 8260B No other oxygenates or lead scavengers were detected The maximum TPH-gas detected was 1 7 mg/kg at 10' bgs in MW-15 using EPA ' Method 8015M No detectable BTEX was identified in the soil column for MW-15 through MW-18 See Figure 2 for well locations ' In August 2005, BEA installed three shallow groundwater wells Momtoring wells MW- 6H-'D 19, MW-20 and MW-21 were advanced to 20' bgs and screened from 5' bgs to 20' bgs See St/ll 4zod/6 Figure 2 for well locations `'t-h jr 3.0) SITE GEOLOGY/HYDROGEOLOGY The site is located on the boundary of the Sacramento Valley and the San Joaquin Valley Y 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 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 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 \mw4-jnw5') mwt,�yn First subsurface water was encountered at depths from 1-1'to.1-2'bgs during tank removal and monitoring well installation at this site in 1?�� an21296 Since then, first subsurface water has been encountered beneath the site between-6'-and tu'bgs The groundwater flow is generally S h v w a western direction beneath the site (See Figure 3, Groundwater Gradient MapJ Historic first Vo subsurface groundwater data identified a west or southwest flow beneath the site Groundwater was also encountered at approximately 35' bgs during installation of deep monitoring wells MW- 12 through MW-16 and MW-18 The potentiometric 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 (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_ During the recent sampling event, groundwater depths were measured between 10 65' And 12 04' from the top of the casing