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Subsurface Investigation, Well Installation, and Sample Analyses Results Page 3 <br /> Cintra Park Phase II Development, <br /> Tract 2705, Tracy, California <br /> July 23, 1998 CTE Job No. 20-0445B <br /> the site the San Joaquin Valley is characterized by a sys em of coalescing alluvial deposits derived <br /> from the nearby California Coast Ranges. Regional topography of the site area slopes gently to the <br /> east, as is typical of the alluvial fan deposits comprising this section of the valley. <br /> n <br /> 6 <br /> � a <br /> r 2.3.2 Geology <br /> ` Based on the San Jose Quadrangle geologic map (Wa er et al , 1990), geologic units in the study <br /> area consist of Quaternary Alluvial Fan (Qf) deposits of the Great Valley Sequence. These units are <br /> composed of interbedded alluvial and aeolian deposits of sand, silt, and gravel. <br /> : . According to a geotechnical investigation by Hallenbeck & Associates (1995), the site is underlain <br /> C by approximately nine to 11 feet of medium stiff to stiff, brown, silty and sandy clays. Soils <br /> underlying these materials (to the total depth explored of 19 feet below grade [fbg]) consisted <br /> generally of soft to medium stiff sandy clays and loose to medium dense, clayey sands and silts <br /> and silty sands. Stratigraphy previously observed by CTE (CTE, 1997) was similar to that <br /> encountered during the previous onsite geotechnical investigation. However, a thin layer (to a <br /> maximum thickness of approximately 2 feet) of fills and/or disturbed soils were encountered <br /> [ . overlying the Quaternary Alluvial deposits. Additionally, an approximately three foot thick and five <br /> foot wide layer of coarse, rounded gravel was found. This layer was determined to have been <br /> i associated with a septic disposal system line. <br /> C:ITEEL FILESICINTRA PAFKICINTRA7-13.DOC <br /> 1 <br /> 1 ' <br />