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SECTION 2.WMU FU-03 BASE AND FINAL GRADING overlies the former Austin Road Landfill and is relatively flat, a geogrid will be placed to support the overlying liners and LCRS. The geogrid calculations are based on both the short-term tensile strength of the geogrid and the long term allowable tensile strength. Because the multiaxial yield strength of geomembranes is about 7 to 10 percent, the specified short term tensile strength of the geogrid is measured at five percent rather than using the ultimate geogrid tensile strength. This requirement maintains strain compatibility by allowing the geogrid to achieve the required tensile strength before the overlying geomembrane deforms beyond its yield strength. Because the tensile strength of geogrids can degrade over time due to factors such as creep installation damage, and other environmental factors, the short-term tensile strength of the geogrid is reduced to calculate a suitable long-term allowable load. The long-term allowable load is compared to the required tensile load in specifying the geogrid properties. The final lifts of refuse on the top deck of the former Austin Road Landfill were placed in 2002. According to site operations personnel,no large metal objects such as refrigerators were placed in the final refuse lifts. The type of refuse placed was municipal solid waste and some construction and demolition debris. It was estimated that the largest void that may collapse in this type of waste has a diameter of approximately 4-ft. Based on the potential that a void of this diameter may collapse directly under the interface lining system, the tensile requirement for the geogrid was calculated to be approximately 550 lbs/ft (Appendix B). 2.4 Refuse Fill Grades Final waste grading plans are not included in this report. This information is available in the Preliminary Closure and Postclosure Maintenance Plan (BAS, 2002). The maximum waste fill slope during the filling of WMU FU-03 will be approximately 3:1, as presented in the slope stability analysis in Appendix B and discussed in Section 3 of this report. The airspace in WMU FU-04 based on 3:1 refuse fill grades is approximately 3.5 million cubic yards. SFO199RPT.DOCI991130002 2A