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File No. 20-1008-48 KI.EINFELDER January 3 , 1992 Having found these cross sections to be in general agreement with the findings of our field explorations, we have utilized these cross sections in our stability analysis of the landfill slopes. In our assignment of soil parameters for the stability analysis, we have attempted to incorporate conservative values into the design. Our soil profile and slope configuration have considered three separate layers; the closure cap material, refuse, and the underlying, undisturbed native soil. A brief discussion of each layer is presented below. Closure Cap It is our understanding that the closure cap will consist of approximately 4 feet of soil overlying the refuse on both the top and side slopes of the primary site and overlying the top of the secondary site. The closure cap material will be composed of on-site as well as possibly imported soil . The closure cap will actually consist of three separate layers; a two foot thick foundation layer of compacted silty sand overlain by a one foot layer of compacted, impermeable clay material which in turn is overlain by one foot of topsoil. In our analysis we have considered these three thin layers as one composite layer. We have assigned a cohesion value to this composite layer of 1000 pounds per square foot (psf) and a friction angle of 30 degrees. We have assumed an average in-place moist unit weight of this material to be 120 pounds per cubic foot (pcf) . Refuse Material As noted earlier, we have found that the refuse on site consists of a mixture of soil, waste and debris. During our field explorations, 17 relatively undisturbed samples within the refuse layer were retrieved and tested in our laboratory. Refuse from other landfills in San Joaquin valley have been noted to have surprisingly high cohesion values (up to 3 , 000 psf) . Typically, the friction value for this material has been lower (between 20 and 25 degrees) . In an effort to remain within conservative bounds in our stability investigation, we have assigned a cohesion value of 350 psf to the refuse material. This correlates to laboratory unconfined compressive strength tests showing cohesion values of approximately 500 psf for the refuse material. A friction angle of approximately 20 degrees was assigned to the refuse material, which again is considered conservative. In our investigation we found dry densities of samples obtained within the refuse layer to vary from approximately 20 to 90 pcf with moisture contents between 7 to 60 percent. For purposes of our stability analysis, we have assumed the refuse material to have an in-place moist density of 120 pcf. Copyright 1992 Kleinfetder, Inc. Page 7 of 9