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Draft Environmental Impact Report Page IV.G-4 Forward Landfill Expansion • A 16- to 20-foot layer of material ranging from silty sand to clayey sand. This layer is dry to moist and typically dense to very dense. • A 5- to 10-foot layer of very stiff yellowish-brown lean clay. This material is moist, with moisture contents between the liquid and plastic limits. • A 30-foot layer of material consisting of very stiff to hard silt and lean clay. This material is moist to wet,with moisture contents between the liquid and plastic limit. • An approximately 80-foot zone of very dense, poorly graded sand was logged starting at an approximate depth between 100 feet. Based on the above subsurface profile, the subsurface soils at the site can be characterized as strong and dense and therefore not subject to significant stability or settlement issues. Soil types that mantle the site vary mainly in their parent material and steepness of terrain. A borrow area exists on the parcel north of the fill area. The landfill areas themselves have removed or covered the native soil with refuse and temporary or permanent cover that cannot support substantial plant growth unless major reclamation measures are applied. According to the U.S. Soil Conservation Service (USSCS, 1992), the existing soil types in the main expansion area typical of Victor Formation sediments that underlie them. The two soil types at the site are Clear Lake clay (CL) and Jackstone clay (ST). These soils are similar in composition,being formed from alluvium. The Jacktone and Clear Lake clays are equally pervasive at the site with the Clear Lake clay more prevalent in the northern and southern portions of the site and the Jacktone Clay more prevalent through the middle portion. These soils are subject to rare flooding in years of abnormally high rainfall over short durations. The Jacktone clay (ST) ST clay covers the nearly flat land 100 to 200 feet from the north and south forks of Littlejohns Creek, and exhibits low soil permeability, moderate water capacity, and high shrink-swell potential with a slight erosion hazard. This type of soil is typically used for irrigated cropland, orchards, and vineyards in the Valley. The ST clay shows a hardpan base at about 60 inches bgs,with low permeability,moderate water capacity,high shrink-swell potential, and low erosion potential. The ST clay is typically 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 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 surface layer of Clear Lake clay (CL) soil 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, available water capacity is moderate, the shrink-swell potential is high,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.