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April 25,2001 ' Job Number:LG01=09$ Page 6 i (Holocene) and Creeks from the Corral,-Hollow Drainage to Brushy Creeks (Plate 2) -The alluvium of the flood plains con"nsists mostly of sand,silt, and'clay- The alluvium named Creeks of the Corral Hollow Drainage to Brushy Creek was deposited chiefly by the Corral Hollow je drainage, Mountain House Creek and Brush Creek. � y • ' The surface and near surface soils located at the proposed new 2 acre parcels are reported to be the Willows Clay..(no. 274) (Plate 3)6. The San Joaquin Soil Survey describes the-soil as the following: "The Willows Clay is.described as a very deep, poorly drained, nearly level saline- sodic soil. Typically, the surface layer is gray clay about 20,inches thick. The subsoil to a depth' ' of,60 inches is,grayish brown,mottled clay. The soil is'ealeareous and saline-sodic throughout. . In some areas the surface'layer is.silty clay. Permeability is very slow in the Willows Clay. Available water capacity is modrate . The shrink-swell potential is high." Table 3 presents some selected.properties of the Willows Clay. Table 3. Selected Soil Properties:of-the Willows Cla,y. San Joaquin County Soil Survey Report.6 Soil Name and Map Depth(iii) Unified Soil Salinity. Soil 'Septic tank �. Symbol Classification minhos/cm Reaction absorption PH -fields i Willows clay,0 to 2 0-20: Clay. C11 . 2-8- 7.9-9.0 •Severer percs. perceni slopes,274.- 20-60:Clay,silty clay. CH. ..>4 8.5-9.0 slowly. . Note: The table descriptions do not necessarily reflect site-specific soil properties. ' A total of Four(4) 6.5-foot deep soil borings were drilled on new parcels.to characterize the subsurface conditions and measure the percolation rate at each location. Plate 1-identifies the 3 locations where the soil borings-and percolation tests were conducted. A table summarizingthe soils,encouritered is presented in the.appendiX. i s Atwater B.F., 1982,Geologic Maps`of the Sacramento-San JoaquinDelta,California:U.S.Geologic I Survey Miscellaneous Field Survey Map MF-1401 21 Sheets, Scale 124,000. 6 USDA Soil Conservation Service, Soil Survey of San Joaquin County,'California, Sheet 12. p !.