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F, <br /> Treadwell&lNIoKIN <br /> r1k <br /> IN <br /> 3.0 GEOLOGIC AND HYDROGEOLOGIC CONDITIONS . <br /> , 1 <br /> The Site is underlain by silts and clays with some shallower silty sands or sandy silt layers. In the <br /> ti" I . <br /> majority of the soil borings drilled at the Site, a sand layer was encountered at approximately 20 to <br /> 21 feet below ground surface (bgs). , n SB-7, the-deepest_soil_boring, sand extended from 70.5 feet bgs <br /> to the maximum depth explored of/kfeet. Groundwater was generally encountered in wells at the Site <br /> at-?5 to 26 feet below ground surface (bgs) . Based on analytical results and the stratigraphy <br /> 'encountered below the site, there are two apparent water bearing zones within 60-feet of the ground <br /> 5 Pi <br /> surface. The shallow groundwater zone was generally <br /> rencogn ered at 30 feet bgs. In the deeper <br /> ), aquifer, groundwater was generally encountered ats5 foi60 feet. Petroleum hydrocarbon concentrations <br /> detected in groundwater in the shallow and deep zones in the same boring were generally significantly <br /> z <br /> 1 <br /> different, further suggesting the presence of two distinct groundwater zones (SBS, SB6, SB7, Tabled) . <br /> Historically, groundwater has been moving generally east to slightly south-east. Historical analytical <br /> results are discussed in Section 5. 0. Boring logs from the 2004 and 2005 investigations are presented <br /> i <br /> in Appendix A. <br /> _.` Historical groundwater elevation data from nearby wells indicates that from 1994 to approximately 1997 <br /> there was a regional rise in groundwater of at least 10 feet. An additional rise in groundwater elevation <br /> was reported to have occurred prior to 1994 (AGE, 2003a; AGE, 2003b; Treadwell & Rollo, Inc., 2004a; <br /> `l Wallace, Kuhl & Associates, 2003). <br /> ' 1 <br /> 4.0 GROUNDWATER MONITORING WELL SAMPLING <br /> =.i <br /> Four groundwater monitoring wells were sampled ten times since July 2002 (Table 2). Prior to well <br /> abandonment, Treadwell & Rollo had Blaine Tech Services sample the groundwater for the final sampling <br /> i <br /> event in December 2004. Previous sampling events were conducted by Ramage. The following sections <br /> discuss the recent monitoring and sampling procedures. <br /> 1 <br /> ' i 4. 1 Groundwater Monitoring Procedure <br /> The total depth anddAeA to groundwater below the top of the well casing were measured to the nearest <br /> — 0.01-foot with an electronic water probe in each well. Groundwater elevations were calculated by <br /> _ subtracting the measured depth to groundwater from the surveyed elevation of the well casing. <br /> 3 <br /> 25971201 . DGD 6 February 2008 <br />