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positive drainage grades would remain even if the estimated maximum differential settlement were to occur. • The liner and LCRS in the 300-ft wide section of WMU FU-08 North that intersects WMU FU- 10 will be connected and leachate from WMU FU-08 North will be routed to the WMU FU-10 sumps. • The edges of the WMU FU-10 liner include termination berms that protect the edge of the liner (see Construction Drawings in Appendix A) and allow connection of the WMU FU-10 lining system to adjacent future WMUs.The berms also define the limits of waste placement. .3 Supported Lining System WMU FU-10 incorporates an interface lining system to separate Class II wastes to be placed in WMU FU-10 from Class III wastes placed in the former Austin Road Landfill. In addition, the connection bench between WMU FU-08 North and WMU FU-10 overlie 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 and LCRS, leachate will pond on the liner, and the potential for infiltration of the leachate into the underlying waste will increase. Typical designs of interface lining systems incorporate measures to bridge over potential voids occurring near the underlying waste surface, which may result from the collapse of a large object, such as a refrigerator. This type of localized collapse is generally considered the worst possible occurrence and therefore is typically the basis for design(Jang,et al., 1993). The conservative "rusted refrigerator" design method was used to develop the requirements for the lining system subgrade. The "rusted refrigerator" design method assumes that a large object completely collapses, creating a void directly below the lining system. This collapse results in a local depression in the lining system. The magnitude of the depression is a function of the separation between the lining and the collapse and can be quantified using elastic solutions (Jang, et al., 1993). The separation/elastic solution methodology was used to assess the magnitude of separation required between the lining system and a potential void for the interface liner. The separation/elastic solution methodology was used to assess the magnitude of separation required between the lining system and a potential void for interface liners to be placed on slopes steeper than 6:1 (horizontaI:vertical). For slopes flatter than 6:1, the magnitude of separation increases exponentially and it becomes cost prohibitive to place sufficient fill to maintain the required separation. WMU FU-10 2.2