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SECTION 2 Base and Final Grading Plans 2.1 General The limits of WMU FU-17 were determined based on the site's operational needs, the landfill site development plan(BAS et al., 2003), and the July 2016 site topographic map. The eastern limit was set based on site operational considerations for airspace. The southern boundary of WMU FU-17 was offset 20-feet from the eventual southern lined excavation slope to allow for operational access to the "wedge"cell that will be constructed to the west. The northern boundary of WMU FU-17 was offset 20-feet from the currently permitted north lined slope due to potential expansion plans to the north. The western boundary of WMU FU-17 connects to WMUs FU-13 and 14. The WMU FU-17 grading plan and liner and LCRS sections and details are included in the Construction Drawings for the development of WMU FU-17 (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 distance between waste in WMU FU-17 and groundwater. 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. The current groundwater elevation in this area is approximately minus 22-feet MSL. The lowest elevation of the WMU FU-17 base lining system is 5-ft MSL (at the top of operations layer) and is located at the eastern boundary. This elevation is approximately 11-feet above the historic high groundwater elevation and 27-feet above current groundwater elevation. It is highly unlikely that historic high groundwater levels will ever re-occur given the high volume of agricultural pumping of groundwater in the area. • WMU FU-17 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 300 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 approximately 0.36 percent. Since the minimum drainage grades on the base of WMU FU-17 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. WMU FU-17 DESIGN REPORT 2-1