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October 12,2000 Job Number.LGllo-312 Page 6 and clay.6 The older Laguna Formation is commonly found along the eastern Sacramento/Central Valley and is composed of interbeded alluvial gravel, sand, and silt.6 Pebbles and cobbles of quartz and metamorphic rock fragments dominate the gravels,but the matrix of the gravelly units and finer sediments are invariably arkosic.6 -The Laguna Formation displays highly dissected rolling topography with tens'of meters of relief 6 The Laguna Formation is estimated to be about 65-feet thick south of Sacramento.` Assuming the well drillers log of the on-site well is reasonably accurate,there were twenty-three(23)measurable layers encountered. The layers located between 4-feet and 232-feet j sand and clay. One 1 l-foot thick gravel layer was in depth are mostly composed of alternating also noted. The thickest sand layer was 24-feet thick beginning at a depth of 14-feet. The thickest top is located at a depth of 120-feet. Most of the sandy layers clay layer was 41-feet thick and the appear to be generally thin and bounded by clay layers of similar thickness. The average,thickness of the sandy layers is 7.8-feet,the average thickness of clay layers is 13.8-feet(see appendix for drillers log). The drillers log, geologic literature,borings, suggest the aquifer is heterogeneous and which probably restricts the downward-vertical flow of recharge from surface sources. The surface soils located at the proposed project location are described by by the San Joaquin County Soil Survey as either the Jahant loam, San Joaquin Sandy Loam, and the San e 7).'For general background information,the following table Joaquin Urban Land Complex(Plat presents some general engineering properties for the given soil. Table of Selected Soil Properties Located on the Site From the San Joaquin County Soil Survey (Plate 7).' Soil Name and Depth(in) Used Soil Salinity Soil Septic tank Map Symbol Classification mmhos/cm Reaction absorption PH fields Jahant loam,2 0-5:Loam. W <2 6.1-7.3 Severe: peres to 8 percent 5-31:Loam,clay loam CL-ML,CL <2 6.17'.3 slowly. Slopes, 183 31-49: Clay,clay loam. CH,CL <2 6.1-7.3 49-53: Cemented 53-6o:indurated- — — — San Joaquin o-10: Sandy loam. SM <2 5.6-6.5 Severe:peres sandy loam,2 to 10 20: Clay loam,clay. CL <2 6.1-7.8 slowly. 5 percent slopes, 20-60-Indurated- — 237 - 237 � s.