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0 3.5.2 Shear Strength of Waste Based on compilation of published data, the RCRA Subtitle D (258) Seismic Design Guidance for Municipal Solid Waste Landfill Facilities (U.S. EPA, 1995) shows a lower -bound shear strength envelope defined by a cohesion intercept (c') of 100 pounds per square foot (psf) and a friction angle (0') of 33 degrees for municipal solid waste (MSW) materials. This RCRA Seismic Design Guidance also shows a conservative unit weight of 65 pounds per cubic foot (pcf) for MSW. These values have been used in the static and seismic slope stability analyses presented herein. 3.5.3 Critical Shear Planes The Module 1 base liner will consist of the following critical shear planes (starting from the top): 1. Operations soil layer-geotextile interface 2. Geotextile-gravel drainage layer interface 3. Gravel drainage layer -textured HDPE geomembrane interface 4. Textured HDPE geomembrane-GCL interface 5. Internal shear plane within the GCL 6. GCL-subgrade interface Because of the presence of the geocomposite drain, the sideslope liner system will consist of the following additional interface (in addition to the above six): 7. Geocomposite-textured HDPE geomembrane interface Of the seven shear planes listed above, the following three have the lowest shear strengths: • Textured HDPE geomembrane-GCL interface • Internal shear strength of the GCL • Geocomposite-textured HDPE geomembrane interface The liner interface/internal shear strength parameters (i.e., adhesion and friction values) typically vary with the normal stress level. At higher normal stresses, the interface/internal shear strength parameters are significantly lower than that at low normal stresses. Because of the weight of waste, the base liner system will be subject to \\.SACRFPi\COMMON\sacDP\2002\PRAP78\83\835608.2bz.doc EMCONIOWT, Inc. Rev. 0, 07/31/02 3-4