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■ <br /> GeologicaI rec/vaa tac. Page 2 <br /> Groundwater Monitoring Report <br /> Project No. 1030.2 <br /> November 18,2004 <br /> (USGS) Topographic Map, Vernalis Quadrangle, California, 7.5 minutes series. A review of <br /> the USGS Topographic Map reveals that the elevation of this site is approximately 75 feet <br /> ' above mean sea level (AMSL). <br /> The site is Iocated on the gradually sloped floor of the northern San Joaquin Valley. The <br /> ' geologic composition of the area is characterized as fluvial deposits of the San Joaquin - <br /> Sacramento River delta system that overlay continental rocks and deposits derived from <br /> erosion of the Sierra Nevada Mountain Range located approximately 50 miles northeast of <br /> Modesto. <br /> The southwest tilting Sierra Nevada fault block underlies the northern San Joaquin Valley <br /> area. Overlying the consolidated rocks are unconsolidated sediments. The lower consolidated <br /> batholithic and metamorphic rocks are poorly transmissive, however the overlying <br /> sedimentary layers are often quite permeable. These unconsolidated layers include <br /> ' Pliocene/Pleistocene age continental deposits, Pleistocene age lacustrine and marsh deposits, <br /> and Holocene older and younger alluviums and flood-basin deposits. <br /> ' 1.2 Regional Stratigraphy <br /> The following information comes from the United States Department of Agriculture — Soil <br /> Conservation Service (USDA). Soil Survey of San Joaquin County, California (McElhiney, <br /> M. A., 1992), indicates the area surrounding the site is predominately made up of one general <br /> ' soil type: <br /> Capay— Stomar--Zacharias: A gentle 0 to 2 percent slope; moderately well drained and <br /> well drained, moderately fine textured, gravelly moderately fine textured, and fine <br /> ' textured soils that are very deep; in interfan basins and on alluvial fans and stream <br /> terraces. <br /> • The USDA Soil Survey of San Joaquin County, California (McElhiney, M. A., 1992), <br /> ' states the soils beneath and adjacent to ST are categorized as: <br /> o Capay clay: Wet 0 to 2 percent slope; very deep, moderately well drained, nearly <br /> level soil is in interfan basins. It formed in alluvium derived from mixed rock <br /> ' sources. Typically the surface layer is grayish brown and dark grayish brown clay <br /> about 20 inches thick and the next 60-inches is typically pale brown silty clay <br /> loam and clay loam. Slow permeability, high shrink-swell potential, low strength, <br /> ' and high water table. <br /> 1.3 Site-Specific Hydrogeology <br /> A site map showing the locations of streets, structures, wells, and other site-related details is <br /> attached as Figure 2. <br /> 1 <br />