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Geological recknics//u. Page 4 Groundwater Monitoring Report Project No.750.2 November 10,2004 consolidated batholithic and metamorphic rocks are poorly transmissive; however the overlying sedimentary layers are often quite permeable. These unconsolidated layers include Pliocene/Pleistocene age continental deposits, Pleistocene age lacustrine and marsh deposits, and Holocene older and younger alluviums and flood-basin deposits. 2.2 Regional Stratigraphy The following information comes from the United States Department of Agriculture — Soil Conservation Service (USDA). Soil Survey of San Joaquin County, California (1992) indicates the area surrounding the COE site is predominately made up of one general soil type: • DELHI — VERITAS — TINNIN: A gentle 0 to 2 percent slope; moderately well drained to somewhat excessively drained, coarse textured and moderately coarse textured soils that are deep to a cemented hardpan or are very deep; on dunes, alluvial fans and low fan terraces. The USDA Soil Survey of San Joaquin County, California (1992), states the area beneath the COE is categorized as Delhi loamy sand with the following description: o Delhi loamy sand— 0 to 2 percent slopes. Very deep, somewhat excessively drained, nearly level soil on dunes. It formed in wind-modified alluvium derived from granitic rock sources. The average annual precipitation is about 11-inches, the average air temperature is about 60° F. 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 August 12, 2004, event was 54.19 -� feet AMSL, which is consistent with previously measured average elevations at the site. The