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Group C Top - approximately 55 to 75 feet deep. Bottom to lowest available data (approximately 110 feet deep). Sediments dominated by sand, fine to medium grained; some coarse grained or gravelly layers. A few layers of silt and clay material occur. Color is generally light brown to yellow brown. Grains are large enough to assess and conclude that the sediments appear to be granitic in origin. Surface Soils. The surface soils are mainly composed of two soil types typical of Victor Formation sediments. The two soils, as mapped by the Soil Conservation Service, are known as Clear Lake clay (CL) and Jacktone clay (ST). These soils are similar in composition; they were formed from alluvium. The most widespread soil type on the site is the Jacktone clay (ST), which covers the nearly flat terrain approximately 100 to 200 feet from the South Fork. Typically, this soil type is found on 0 to 2 percent slopes forming a moderately deep hardpan of somewhat poorly drained soil made up of generally dark gray clay about 2 inches thick, underlain by light gray clay loam, followed by hardpan of 3 inches. Permeability is low, the available water-holding capacity is moderate, the shrink-swell potential is high, water may be perched on top of the hardpan following heavy rain, runoff is slow, and the water erosion hazard is slight. The typical uses of this soil type are irrigated cropland, orchards, vineyards, and sometimes irrigated pasture and urban development. The Clear Lake clay soil type is common along the South Fork. The surface layer is dark gray clay about 29 inches thick followed by another 8 inches of dark gray clay, then 5 inches of mixed light brownish gray clay loam, then variegated dark grayish brown weakly to strongly cemented hardpan to a depth of 60 inches. The permeability of this soil is low, the available water-holding capacity is moderate, the shrink-swell potential is high, the water erosion hazard is low, and the soil is subject to rare flooding during abnormally high rainfall events. This soil type is typically used for irrigated cropland, orchards, and sometimes irrigated pasture and urban development. Soil Properties. Subsurface soil properties onsite have been evaluated during three separate soil investigations. The first investigation of the onsite subsurface soils was performed by EMCON Associates in 1972. EMCON drilled a total of 17 borings ranging in depth from 38 feet to 178 feet. The locations of the EMCON boreholes are shown on the Existing Conditions Plan (Drawing 1) of that report. Another subsurface investigation was performed by InsituTech in 1987 using Cone Penetration Testing (CPT) in the WMU E area. The exact locations of the CPTs were, unfortunately, not surveyed by InsituTech. The subsurface investigation was performed by CH2M HILL in 1992; it consisted of four soil borings drilled in April and May, 1992. The Existing Conditions Plan (Drawing 1) of that report shows the approximate location of these four borings, designated as BH-1 through BH-4. Pitcher Drilling Company of Palo Alto, California, was subcontracted to drill the soil borings. CH2M HILL personnel specified the locations, depths of borings, and sampling intervals and observed the drilling and sampling operations. All borehole logs available for the site are included as an appendix in that report. Forward Composting Facility RCSI 7/20/09;Page 20 SWT Engineering