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550 feet, or approximately 0.36 percent. Since the minimum drainage grades on the base of the southern portion of WMU FU-08 are 1 percent and the net effective slope to the LCRS pipes is at least 2 percent, positive drainage grades would remain even if the estimated maximum differential settlement were to occur. • Because the northern portion of WMU FU-08 overlies the interim final cover for the former Austin Road Landfill, the base grades for this portion of the cell are consistent with the final grades of the interim final cover. As discussed in the Settlement Analysis, Interim Cover;Austin Road Landfill (Geologic Associates, April 2002), the grades are based on maintaining positive drainage once refuse is placed above the interim final cover. The interim final cover and, therefore,the base of northern portion of WMU FU-08 generally grades at 3 percent to the south. The post-settlement grades of the northern portion of WMU FU-08 are expected to remain at approximately two percent to the south. • Leachate collected in the northern portion of the cell that overlies the former Austin Road Landfill will be collected along the southern berm located along the southern boundary of the former Austin Road Landfill top deck and routed to temporary leachate tanks via a 3-inch dia. HDPE pipe. Once the southern portion of WMU FU-08 is approved for disposal by the RWQCB, the western portion of the southern termination berm on the former Austin Road Landfill top deck will be removed. The liner and LCRS in the northern and southern portions of WMU FU-08 will be connected and leachate routed to the WMU FU-08 sumps. • Only Class III wastes will be placed in the northern portion of WMU FU-08. Class III refuse placement in the northern portion of the cell will extend a minimum of 50-ft to the south of the boundary of the northern and southern portions of WMU FU-08 and the southern most Class III refuse face will be sloped to the south. • The edges of the WMU FU-08 liner include termination berms that protect the edge of the liner (see Construction Drawings in Appendix A) and allow connection of the WMU FU-08 lining system to adjacent future WMUs. The berms also define the limits of waste placement. 2.3 Supported Lining System WMU FU-08 incorporates an interface lining system to separate Class II wastes to be placed in WMU FU-08 from Class III wastes placed in the former Austin Road Landfill. In addition, the connection bench between the WMU FU-08 northern and southern portions overlies refuse. 2.3.1 Analytical Method Because the interface lining systems overlie refuse, settlement is an important element of the interface liner design. A lining system constructed over an existing landfill is potentially subject to differential settlements that may occur because of the variable compressibility of different wastes and/or the collapse or degradation of large objects within the landfill. Differential settlements in the subgrade of an interface liner could result in tensile strains at the surface of the liner system and could affect the drainage capacity of the lining system's LCRS. If the tensile strains within the liner exceed the tensile capacity of the lining material, tensile failure could develop. Under extreme conditions, tensile failure will reduce the effectiveness of the liner as a hydraulic barrier by providing a direct flow path through the lining system. Additionally, differential settlements could affect the slope at which the lining system had been constructed and could possibly result in the reversal of leachate drainage grades. If grade reversal takes place at the surface of a liner WMU FU-08 2-2