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2.0 SITE CONDITIONS <br /> 2.1 GEOLOGY <br /> The site is located within the Great Valley geomorphic province. The Great Valley is a <br /> northwest trending structural trough, which borders the Sierra Nevada to the east and <br /> the Coast Ranges to the west. It is underlain by a thick sequence of sedimentary units, <br /> including Quaternary alluvial deposits. Subsurface soils beneath the site consist of both <br /> fine-grained soils (clays and silts) and coarse-grained soils (sands and silty sands) of <br /> varying thicknesses to the total explored depth of 100 feet below grade (fbg). <br /> Cross-sections are provided as Appendix B. <br /> 2.2 HYDROGEOLOGY <br /> Current depth to water in the site wells ranges from approximately 33.8 to 36.2 fbg. <br /> Initially,when groundwater monitoring began in 1990, groundwater was nearly as deep <br /> as 60 fbg. Groundwater rose until the years 2000 and 2001, when groundwater depths <br /> were approximately 31 fbg. Groundwater flow is consistently towards the east. The <br /> groundwater gradient is relatively flat, typically ranging from 0.002 to 0.004 ft/ft. <br /> Figure 2 depicts groundwater contours and flow direction based on first quarter 2009 <br /> groundwater monitoring data. A contour depicts a slight depression effect around well <br /> MW-4. Historical monitoring well data is provided as Appendix C. <br /> 2.3 DISTRIBUTION OF HYDROCARBONS IN SOIL <br /> Soil sample results indicate the highest hydrocarbon concentrations were located near <br /> the former UST complex at depths ranging from 15 to 50 fbg. March 1990 soil samples <br /> from boring.B-3 contained up to 17,000 parts per million (ppm) TPHg and 400 ppm <br /> benzene at 15 fbg. Based on the soil analytical data, total petroleum hydrocarbons as <br /> gasoline (TPHg) is defined laterally in unsaturated soil in all directions by well borings <br /> MW-1 through MW-4 and borings B-2, B-6, B-7, Geo-3, and SB-1. Benzene is defined <br /> laterally in unsaturated soil in all directions by well borings MW-1 through MW-5 and <br /> borings B-6,Geo-3,and SB-1. <br /> Shell installed one soil vapor extraction (SVE) well (VEW-6) and four dual-phase <br /> extraction (DPE) wells (VEW-3, VEW-4, VEW-5, and VEW-7) in January 2006. Soil <br /> results indicated that petroleum hydrocarbons, methyl tertiary-butyl ether (MTBE), <br /> tertiary-butyl alcohol (TBA), 1,2-dicholoroethane (1,2-DCA), and ethylene dibromide <br /> XXXXx(xxJ 2 CONESTOGA-ROVERS&ASSOCIATES <br />