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SECTION 2 Base and FinalGrading s 2.1 General The limits of WMU FU-10 were determined based on the site's operational needs, the landfill site development plan (BAS et al., 2003), and the April 2009 site topographic map. The southern limit was set to maintain the main access road into the facility. The southern boundary of WMU FU-10 will eventually be connected to the northern boundary of WMU D-02. The northern limit was established at the southern limit of WMU FU-08 North. The western limit of WMU FU-10 connects to WMU FU-08 and the eastern limit is based on site operational considerations for airspace. The WMU FU-10 grading plan and liner and LCRS sections and details are included in the Construction Drawings for the development of WMU FU-10 (Appendix A). Permanent access roads and surface drainage facilities will be constructed as the WMU meets final grades. 2.2 Liner and LCRS Grades Design criteria and reasoning to develop the grading plan includes: • Title 27 requires a minimum 5-foot barrier between waste in WMU FU-10 and groundwater. Additionally, the site WDRs require that no waste be discharged below an elevation of 7 feet above MSL. The lowest elevation of the WMU FU-10 base lining system is 15.1-ft MSL (at the top of operations layer) and is located at the eastern boundary. This elevation is significantly above the WDR requirement of a minimum elevation of 7 feet MSL. • Based on the "Forward Landfill Groundwater Elevation Evaluation East of WMU FU-06" and the "Forward Landfill Expansion, Groundwater Elevation Evaluation" (GeoLogic Associates, 2007) (see Appendix B), the maximum high groundwater elevation underlying the area east of WMU FU-06 is anticipated to be minus 6-feet MSL. In the RWQCB's letter dated 14 December 2007 (see Appendix B), the RWQCB concurred with GeoLogic Associate's evaluation of high groundwater elevation. Forward is planning to amend the WDRs to state that the minimum elevation for refuse disposal should be at minus 1-ft MSL, which is 5-feet above the maximum high water table. • WMU FU-10 will be graded to drain to east-west trending leachate collection pipes that lead to temporary sumps. The maximum drainage distance to the pipe is approximately 150 feet(see the Construction Drawings in Appendix A). • As outlined in the Preliminary Closure and Postclosure Maintenance Plan (CH2M HILL, 1994e), abrupt differential foundation settlement is not anticipated in the onsite soils forming the base grades of the landfill. The estimated maximum differential foundation settlement is 2 feet in 550 feet, or approximately 0.36 percent. Since the minimum drainage grades on the base of WMU FU-10 are 1 percent and the net effective slope to the LCRS pipes is at least 2 percent, WMU FU-10 REPORT 2-1