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SECTION 2.WMU FU-03 BASE AND FINAL GRADING • Because the northeastern portion of WMU FU-04 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 northeastern portion of WMU FU-04 generally grades at 3 percent to the south. The post-settlement grades of the northeastern portion of WMU FU-04 are expected to remain at approximately two percent to the south. • Leachate collected in the northeastern 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 the WMU FU-04 base LCRS via a 3-inch dia. HDPE pipe. Once refuse placement in the central portion of WMU FU-04 approaches the top deck of the former Austin Road Landfill, the southern berm will be removed and leachate routed directly into the LCRS of the central portion of WMU FU-04. • Only Class III wastes will be placed in the northeastern portion of WMU FU-04. Class III refuse that will be placed in the northeastern portion of WMU FU-04 will eventually be overlain with an interface liner to separate it from the Class II wastes that will be placed in the central portion of WMU FU-04. • Leachate collected on the interface liner in the northwestern portion of the cell will be routed directly south into the WMU FU-03 LCRS. • The edges of the WMU FU-04 liner include termination berms that protect the edge of the liner (see Construction Drawings in Appendix A) and allow connection of the WMU FU-04 lining system to adjacent future WMUs.The berms also define the limits of waste placement. 2.3 Supported Lining Systems WMU FU-04 incorporates interface lining systems to separate Class I1 wastes to be placed in WMU FU-04 from Class III wastes placed in adjacent portions of the landfill. The interface lining systems are located in the central portion of WMU FU-04, where the cell overlies the former Austin Road Landfill, and in the northwestern portion of WMU FU-04, where the cell overlies refuse placed in WMU ART-03 and the former Austin Road Landfill. Because these 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. SFO/99RPT.DOC/991130002 2-2