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0 2. PHYSIOGRAPHIC AND HYDROGEOLOGIC SETTING The Great Central Valley of California consists of ancient alluvium ranging in depth of less than 20 feet near the bedrock highs on the rolling hills to the east and up to over 20,000 feet below ground surface (bgs) near the center of the basin. These sediments are comprised of terrestrial, marine and volcanic sediments deposited during periodic inundation by the Pacific Ocean and erosion of the surrounding mountains respectively. Sediment deposits beneath the site can be subdivided into consolidated and unconsolidated deposits, with the consolidated sediments underlie the unconsolidated sediments. With depth the stratigraphy of unconsolidated sediments consist of Recent to Pleistocene Age alluvial deposits of the Modesto,Riverbank Formations. Sediments encountered consist of unconsolidated sands and gravels interbedded with significant silts and clays. These clays separate the upper sediments from the lower Late Plio- Pleistocene Age Laguna Formation and the older Eocene to Pliocene Age Mehrten Formation, these units are poorly consolidated sediments and are differentiated based on color and sand type. The Laguna formation is typical light brown of color, and the differentiated characteristic of the Mehrten is the black sands derived from volcanic detritus. Valley Springs and Ione formation are known to exist below the Mehrten Formation. The formations have a distinct geologic dip and thickness to the west. The Laguna and Mehrten Formations ranges from 200 to 1,000 feet in thickness from east to west. SITE SPECIFIC SOILS AND GEOLOGY The Woods Dairy site lies within alluvial deposits with parent materials originating from sandy granitic alluvium. Based on Web Soil Survey 2.1 through the National Resource Conservation Service, soils found at the Woods Dairy site are composed of sandy loam to fine sandy loam. Soil units consist of the Acampo and Devries sandy loams and the Tokay fine sandy loam. The Acampo sandy loam is a low salinity, moderately well drained soil with duripan at 40 to 60 inches below surface. The Devries sandy loam is a low salinity, somewhat poorly drained soil with duripan at 20 to 40 inches below surface. The Tokay fine sandy loam is a low salinity, well drained soil with no restrictive features within 80 inches of surface. The Acampo and Devries sandy loams underlie the majority of the fields, with the Tokay underlying less than 20%. Woods Dairy March 1,2010 103-27 Monitoring Well Installation Plan 6 Revision 1