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To maximize the fill capacity, the liner system in each module should meet or exceed the assumed residual shear strength defined by a friction angle of 12 degrees. However, slightly lower liner shear strength may be acceptable in some of the modules where the interim slope stability is less critical than in Module 9. The actual shear strength requirement within each module may be determined in the future during the design of the individual modules, based on both interim and global slope stability analyses of each module. The shear strength of the liner system within each of the future modules should be verified using large-scale direct shear testing (ASTM Method D5321), as part of the construction quality assurance program. The maximum waste height within these modules is 255 feet, which corresponds to a maximum normal stress of approximately 20,000 psf. Therefore, the shear strength of the liner systems in Modules 5 through 11 should be tested to a maximum normal load of 20,000 psf. The liner shear strength and testing requirements are summarized in Table 3. As noted in this table, the shear strength of the interface between the GCL and textured HDPE geomembrane should be tested with actual materials proposed for construction of the composite liner. A needle -punched GCL with nonwoven geotextile on both sides should be used in the liner construction. If a geotextile cushion is used above the geomembrane, the interface between the textured geomembrane and the geotextile should be tested to make sure that this interface also meets the 12 degree friction angle requirement. The following procedure is recommended while evaluating the measured shear strength test data: + If the measured large -displacement shear strength values (corresponding to 3 -inch shear displacement) at all four normal loads listed in Table 3 are greater than those specified, the test results are acceptable. + If the measured large -displacement shear strength values at all four normal loads are less than those specified in Table 3, the test results are not acceptable. + If the measured shear large -displacement shear strength values at the lower normal stresses (5,000 and 10,000 psf) exceed those specified in Table 4, but the measured shear strength value at the higher normal stresses (15,000 and 20,000 psf) do not meet those specified in Table 3, the slope stability analysis should be re-evaluated to verify if the measured shear strengths meet the design criteria discussed in Section 2.2. 9.2.2 Leachate Pipes within the Future Modules Since an SDR 15.5 leachate pipes shows an inadequate factor of safety against wall crushing, an SDR 13.5 HDPE leachate collection pipes should be used within the future modules. Geotechnical Analyses for NCRCSL Department of Public Works/Solid Waste Shaw Environmental, Inc. County of San Joaquin, December 12, 2007 9-3