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08 September 2009 <br />AGE -NC Project No. 03-1055 <br />Page 9 of 19 <br />2.5. SOIL PROPERTIES <br />Silty clay and clayey silt with a silty sand layer around 10 feet and 15 feet bsg were encountered <br />northeast of the former UST, while silty clay and clayey silt with a sand layer at 15 feet was <br />encountered southeast of the former UST. Silt with clay or silty sand was encountered west of the <br />former UST. A sand layer from 10 feet to 15 feet bsg was encountered adjacent to the former UST. <br />Monitoring well logs, soil boring logs and construction specifications are presented in Appendix I. <br />Geologic cross sections are depicted on Figures 4, 5 and 6. <br />2.6. REGIONAL GEOLOGIC SETTING <br />The site is situated within the southern portion of the Great Valley Geomorphic Province of <br />California, a large, elongate, northwest trending, asymmetric structural trough. The northern and <br />southern portions of the Province have been designated the Sacramento and San Joaquin Valleys, <br />respectively. The Province is bordered by the Coast Ranges to the west, the Klamath Mountains and <br />Cascade Range to the north, and the Sierra Nevada to the east. <br />1 The Great Valley has been filled with sediments derived from both marine and continental sources. <br />Thickness of the sedimentary fill ranges from thin veneers along the valley edges to more than <br />20,000 feet in the south central portion of the valley. The sedimentary formations range in age from <br />Jurassic to Recent, with the older deposits being primarily marine in origin and the younger deposits <br />being primarily continental. Continental -derived sediments were primarily deposited in lacustrine, <br />fluvial, and alluvial environments with sediment sources being the mountain ranges surrounding the <br />valley (Olmsted and Davis, 1961). The site itself is located on unconsolidated and semi -consolidated <br />alluvium, lake, playa and terrace deposits of Quaternary age (California Division of Mines and <br />Geology, 1977)_ Rocks composing the basement complex of the Province have not been completely <br />defined but are believed to be metamorphic and igneous in origin. <br />The Modesto, Riverbank and Turlock Lake Formations and overlying recent alluvium are the <br />principal source of domestic ground water in the 13,500 -square -mile San Joaquin Valley Ground <br />Water Basin (Basin 5-22). This basin is drained primarily by the San Joaquin River. <br />3.0. ASSESSMENT OF HYDROCARBON -IMPACTED SOIL <br />Between May 2000 and May 2008, 27 soil borings were advanced for the collection of soil samples; <br />a total of 84 soil samples were analyzed within this time period to assess the extent of hydrocarbon - <br />impact to soil. <br />Advanced GeoEuvironmental, Ines <br />