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SECTION 2 Base and Final Grading Plans 2.1 General The limits of WMU FU-06 were determined based on the site's operational needs, the landfill site development plan(BAS et al.,2003),and the February 2006 site topographic map. The southern limit was offset 50 feet from the property line to allow for an access road and for the future final cover. The northern limit in the northern portion of the cell was based on the northern extent of the former Austin Road Landfill top deck,with an allowance for a 25-ft access road. The western limit of WMU FU-06 connects to WMU FU-05 and the eastern limit is based on site operational considerations for airspace. The WMU FU-06 grading plan and liner and LCRS sections and details are included in the Construction Drawings for the development of WMU FU-06 (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-06 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-06 base liner in the southern portion of the cell is in the primary sump and was set to comply with the WDRs at an elevation of 7 feet MSL. • According to the San Joaquin County Flood Control District, the historic high groundwater table is approximately 10 feet below MSL. If the historic high were to occur, a waste to groundwater separation of approximately 17 feet would be maintained. • The southern portion of WMU FU-06 will be graded to drain to north-south trending leachate collection pipes that lead to a permanent sump. 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(approximate elevation of 15-ft MSL)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 the southern portion of WMU FU-06 are greater than 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. • Because the northern portion of WMU FU-06 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 WMU FU-06 REPORT 2-1