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Ms.Lori Duncan C A M B R I A September 9,2005 Site Geology The site is located within the Great Valley geomorphic province. The Great Valley is a northwest trending structural trough, which borders the Sierra Nevada to the east and the Coast Ranges to the west. It is underlain by a thick sequence of sedimentary units, including Quaternary alluvial deposits. Subsurface soils beneath the site consist of both fine-grained soils (clays and silts) and coarse- grained soils (sands and silty sands) of varying thicknesses to the total explored depth of 100 fbg. Boring logs and cross sections are provided as Attachment B. © Hydrogeology Current depth to water in the site wells ranges from approximately 35 to 37 fbg. Initially, when groundwater monitoring began in 1990, groundwater was nearly as deep as 60 fbg. Groundwater rose until the years 2000 and 2001, when groundwater depths were approximately 31 fbg. Since then, groundwater depths have dropped to current levels. Groundwater flow is consistently towards the east. The groundwater gradient is relatively flat, typically ranging from 0.002 to 0.004 ft/ft. Figure 3 depicts groundwater contours and flow direction based on second quarter 2005 groundwater monitoring data. Distribution of Petroleum Hydrocarbons Distribution of Petroleum Hydrocarbons in Soil: Soil sample results indicate the highest hydrocarbon concentrations are located near the former UST complex at depths ranging from 15 to 50 fbg. Soil samples from boring B-3 contained up to 17,000 ppm TPHg and 400 ppm benzene at 15 fbg. Based on the soil analytical data,TPHg is defined laterally in unsaturated soil in all directions by well borings MW-1 through MW-4 and borings B-2, B-6, B-7, Geo-3, and SB-1. Benzene is defined laterally in unsaturated soil in all directions by well borings MW-1 through MW-5 and borings B-6,Geo-3, and SB-1. Distribution of Petroleum Hydrocarbons in Groundwater: Quarterly groundwater monitoring began at the site in the third quarter 1990. The highest current TPHg and BTEX concentrations detected in on-site wells are from well VEW-2. Petroleum hydrocarbons are defined in groundwater to the north by wells MW-1 and MW-2 and to the west by well MW-5. Benzene is also defined in groundwater east of the site by well MW-12. TPHg is defined below 200 ppb south of the site by well MW-3 and to the east by MW-12. Benzene is defined below 1 ppb in well MW-3. Well MW-7, located cross-gradient of the site, also contains TPHg and benzene. Cambria notes that concentrations in MW-7 are higher than those in wells MW-3 and MW-6, which are located between the former on-site USTs and MW-7. 5