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KLEINFELDER <br /> File No. 20-1008-38 <br /> August 1, 1990 <br /> layer acting as the closure cap. Typical cross sections of both <br /> the primary slope and the secondary slope are shown on Plate I and <br /> II, attached. <br /> r Our soil profile slope configuration considered 3 materials: The <br /> ._ closure cap, the refuse for the landfill, and the underlying native <br /> soil condition. A discussion of each follows. <br /> CLOSURE CAP• <br /> We understand that the closure cap will consist <br /> of 3 separate materials. The bottom layer will <br /> be a 2-foot thick foundation layer which <br /> t typically consists of on-site native material. <br /> A 1-foot thick clay layer with a maximum <br /> permeability of 1 X 10-6 cm per second will <br /> cover the foundation layer. The top 1-foot <br /> will be topsoil. We anticipate the closure <br /> cap to be relatively insignificant with regards <br /> to slope stability. Therefore, in order to <br /> simplify our study, we have treated the closure <br /> cap as a single 4-foot thick layer. Officials <br /> at the California State Regional Water Quality <br /> Control Board have confirmed our assumption. <br /> We have assumed cohesion to be 750 pounds per <br /> square feet (psf) friction to be 25 degrees <br /> and the moisture unit weight to be 110 pcf. <br /> It is our opinion that these strength values <br /> will be conservative since low permeability <br /> clay will often have cohesion over 2,500 psf, <br /> and native sands can have friction angles <br /> 2 • <br />