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4.0 <br /> SOILS, GEOLOGY AND SEISMICITY <br /> 4.1 REGIONAL GEOLOGY <br /> The site is located within the northern portion of the San Joaquin Valley (Great Valley Geomorphic <br /> Province of California) The Great Valley is a northwest trending structural trough, approximately 400 <br /> miles long and averaging 50 miles wide, that is filled with Cretaceous, Tertiary and Quaternary period <br /> sediments. The province is fault-bounded on the west by the Coast Ranges, and bounded on the east by <br /> the Sierra Nevada foothills with the bedrock of the Sierra Nevada block dipping gently westward <br /> beneath the valley sediments. The sedimentary formations comprising the valley fill are nearly flat-lying <br /> and are derived from erosion of the Sierra Nevada and the Coast Ranges. Gently westward dipping <br /> Tertiary volcanic flows and ash from the Sierra Nevada cover older marine and delta deposits,and in turn <br /> are covered by lake and alluvial deposits in the northern portion near the eastern edge of the valley. The <br /> western extent of the valley is filled by thousands of feet of sediment with the deepest filling in the <br /> southwestern portion being more than 30,000 feet thick. <br /> The Cahfonia Division of Mines and Geology Geologic Map of the Sacramento Quadrangle,California,1:250,000 <br /> identifies the underlying sedimentary unit in the area of the project as being the Modesto Formation <br /> alluvium—Qml(upper member). The sedimentary material is described as"arkosic alluvium." <br /> 4.2 SITE GEOLOGY <br /> The Site is located in an area that exhibits a fairly complete stratigraphic section of Cretaceous,Tertiary, <br /> and Quaternary deposits. The soils study consisted of a compilation of available public soils data from <br /> the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) <br /> Web Soil Survey (WSS) Online Soil Mapping accessed April 24, 2008. The study included a site <br /> reconnaissance and observation of exposed soil profiles. According to the USDA WSS,the project site is <br /> located within the Devries sandy loam map unit. The Devries map unit is composed of somewhat poorly <br /> drained sandy loams derived from mixed rock sources and deposited as alluvium. <br /> The average annual temperature is approximately 60 degrees F., average annual precipitation is <br /> approximately 15 inches, and the frost-free season approximately 270 days (USDA WSS, accessed April <br /> 24,2008). <br /> 4.3 GEOLOGIC HAZARDS <br /> 4.3.1 Expansive Soils <br /> Expansive soils are defined as soils that undergo large volume changes (shrink or swell)due to variations <br /> in moisture content. Such volume changes may cause damaging settlement and/or heave of foundations, <br /> slabs-on-grade,pavements,etc. <br /> Based upon the observations during the subsurface exploration,expansive soils may be present onsite. It <br /> is anticipated that damage potential due to onsite expansive soils will be low and can be mitigated using <br /> standard design and construction techniques. Geotechnical investigations should be completed to <br /> support project design and construction, evaluate areas that may be subject to expansive soils, and <br /> evaluate the expansion potential beneath the site. <br /> 4.3.2 Collapsible Soils <br /> Collapsible soils are defined as a soil that will undergo a sudden decrease in volume when its internal <br /> structural support is lost. Internal support is a temporary strength derived from numerous sources, <br /> Project No.5593-01-05 C A R LT O <br /> 7/29/2008 6 Engineering Inc . <br /> NCPA GFS.doc <br />