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1117 Lone Palm Avenue, Suite <br /> Modesto, CA 953511 <br /> (V <br /> www.atcassociates.com <br /> 209-579-2221 <br /> ASS o c t ATE s i N c . Fax 209-579-2225 <br /> Environmental, Geotechnical and Materials Engineers <br /> 3 .0 SUBSURFACE CONDITIONS <br /> 3_1 Geology <br /> The drill cuttings logged from off-site monitoring well MW13 generally consisted of clay to <br /> approximately 20 feet bgs and sandy clay from 20 to 60 feet bgs. Soil consisting primarily of silt <br /> and silty clay was encountered in the borehole of MW14 from the surface to approximately 40 <br /> feet bgs and was underlain by sandy silt and sandy clay to approximately 58 feet bgs. Silty sand <br /> was encountered from approximately 58 feet to 61 . 5 feet bgs. <br /> As previously indicated in Section 2 . 1 , the lithology previously logged for MW6 is assumed to <br /> be similar for MW15 to approximately 85 feet bgs and generally consisted of clays from the <br /> surface to approximately 15 feet bgs . Soil consisting primarily of silty and clayey sands was <br /> encountered between approximately 15 to 35 feet. Soil encountered between approximately 35 <br /> to 60 feet bgs consisted of clays and silts. Soils consisting of sands with increasing silt and clay <br /> fractions with depth were encountered from approximately 60 feet to approximately 80 feet bgs. <br /> Sandy clay was encountered from approximately 80 to 86 feet bgs . While drilling the borehole <br /> for MW15 , sand was encountered from approximately 85 to 136 feet bgs and was underlain by <br /> clay from approximately 136 to 141 feet bgs. Sand was encountered from approximately 141 to <br /> 154 feet bgs. Soil boring logs with detailed descriptions of soil types are contained in Appendix <br /> A. <br /> 3.2 Hydrogeoloey <br /> Water levels were measured in monitoring wells MWl through MW10, MW11R, and MW12 <br /> through MW15 December 7, 2006. Water levels in the shallow zone (MW1, MW2, MW3, <br /> MW8, MW9, MW10, MW11R, MW13 , and MW14) ranged from 43 . 53 to 45 .22 feet below the <br /> tops of the well casing elevations. Water levels in the intermediate zone wells (MW4, MWS, <br /> MW6, and MW12) ranged from 44. 55 to 45 .42 feet below the tops of well casing elevations . <br /> Water levels in the deepest wells, MW7 and MW15 , were 44.58 and 44. 92 feet below the tops of <br /> the respective well casing elevations. The water level data were used to develop groundwater <br /> elevation contour maps (Figures 4 and 5) . Groundwater flow in the shallow zone was variable <br /> with an apparent depression in the center of the site in the vicinity of MW1 and MW8 . <br /> Groundwater flow in the intermediate zone was towards the north. The average hydraulic <br /> gradient in the intermediate zone on December 7 , 2006, was calculated to be 0.0045 ft/ft or <br /> approximately 24 ft/mile. A summary of groundwater monitoring data is presented in Table 2 . <br /> 4.0 ANALYTICAL RESULTS <br /> None of the analytes of interest were detected in the groundwater samples collected from MW7, <br /> MW10, MW11R, MW13 , MW14, and MW15 . BTEX constituents were detected in the <br /> groundwater samples collected from MWI , MWS , MW6, and MW8 . The highest concentrations <br /> S:\Env iromental\28349kepoi ts\sum.doc 5 ATC Associates Inc. <br />