ARCHIVED REPORTS_2022 [REV] RCSI W/CHANGES

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2-11 Forward Composting Facility SWT Engineering Report of Composting Site Information - August 2019January 2022 z:\projects\allied waste\forward\resource recovery facility\5 yr permit rvw 2019-2020\rcsi 2019\text\sec 2.doc northeast. The sediments have been divided into three large groups based on gross lithology and pervasive distinctions in color. Although several st rata can be recognized in the logs, for purposes of this report they were grouped into the following three larger groups: Group A Surface to approximately 28 to 40 feet below ground; highly interbedded sandy silt, clayey silt, silt, and clay. A few layers of sand are present. Generally sands are fine grained. Most of the sediments have an oxidized appearance, showing an orange brown color. Group B Top - approximately 28 to 40 feet deep to bottom: approximately 55 to 75 feet deep (25 to 35 feet thick); interbedded sand, silty sand, silt, and a little clay. Sands are fine grained. Overall, this layer is a little sandier than Group A. Sediments are distinctly less oxidized than G roup A showing a grey brown color. Group C Top - approximately 55 to 75 fee t deep, bottom (approximately 110 feet deep): Sediments dominated by fine-to-medium grained sand; 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 eno ugh 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 U. S. Soil Conservation Service, a re known as Clear Lake clay (CL) and Jacktone 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 s outhern 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 most widespread soil type on the site is the Jacktone cla y (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 he avy 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 Nort h Fork and South Fork of South Littlejohn’s Creek . 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 t o 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. Soil Properties . Subsurface soil properties have been evaluated in several geotechnical investigations. The first investigation of the on-site subsurface soils was performed by