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Geologkaf rechnics ta. Page 5 Groundwater Monitoring Report Project No.750.2 April 1,2005 2.3 Site-specific Hydrogeology 2.3.1 Lithology and Soil Characteristics • Top two feet of the site appears to be backfill materials comprised of gravel and sand • Brown, poorly sorted, sand from 5 to 10 feet bgs, which overlies a dry, light brown, silt unit between 10 and 20 feet bgs • The geology from 20 to 30 feet bgs consists of various layers of grey colored silt and sand • The predominant geology between 30 and 45 feet bgs is comprised of a buff color, poorly sorted sand containing some clasts greater than 1 centimeter in size • Grey silt and sandy silt layers were noted between 43.5 and 50 feet bgs • Sand characterizes the 50 to 55 foot interval —buff and well sorted at 50 feet bgs grading down to brown and poorly sorted at 55 feet bgs A site map showing the locations of streets, structures, wells, and other site-related details is attached as Figure 2. 2.3.2 Groundwater Bearing and Gradient The average groundwater elevation measured during the February 16, 2005, groundwater- monitoring event was 55.06 feet AMSL, which is consistent with previously measured groundwater elevations at the site. The groundwater elevation increased approximately 0.98 —"-" feet since the November 26, 2004 monitoring event. Depth-to-water measurements averaged 65.09 feet bgs. Groundwater gradients were calculated for the November 2004, event using MW-1, MW-2 and MW-3. Groundwater was flowing N85°W with a gradient measuring 0.0018 ft/ft. The elevation, gradient and bearing data are summarized in Table 1 of Appendix A. The groundwater gradient is illustrated on Figure 3: Groundwater Gradient Map. Historical groundwater directions and gradients are presented in Figure 4: Rose Diagram, which shows a historically westerly flow direction. As required under AB2886, the depth to groundwater data was submitted electronically to GeoTracker on April 4, 2005, with confirmation number 7843449234. 2.3.3 Vertical Groundwater Gradient For the February 16, 2005, groundwater measurement, the vertical gradient was calculated for the MW-1/MW-101 pair. The vertical gradient was negative (a downward direction). However, it was insignificant due to a near zero head difference between MW-1 and MW- 101. The vertical groundwater gradient is less than the horizontal groundwater gradient. Generally,the magnitude of the vertical gradient has decreased since February 2001. v w