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SECTION 4 WMU FU-03 Surface Drainage and Desilting Basin WMU FU-03 has been designed to minimize the amount of leachate generated within the unit by grading surface waters away from the excavated unit and into storm water control features. The area surrounding the perimeter of WMU FU-03 will be graded away from the crest of the excavation. The grading will reduce surface water run-on into WMU FU-03 from adjacent areas. Precipitation that falls within the confines of WMU FU-03 and contacts waste will be collected and removed through the LCRS and treated as leachate. The LCRS has been sized to handle twice the anticipated daily leachate volume from the 1,000-year, 24-hour storm event during filling (see Section 5.2). Surface drainage facilities on the final waste fill will be incorporated when final grades are met and the final cap has been constructed. These drainage considerations are discussed in the Preliminary Closure and Post-Closure Maintenance Plan (BAS, 2002), and the Final Design Study for the Austin Road Landfill Expansion ,R. W. Beck and Associates(June 1993). The R. W. Beck study indicates that at full development, approximately 13.0 acre feet of detention capacity will be necessary to limit discharge into Little John's Creek to 100 cfs for the 100-year storm. The proposed desilting basin is designed for an interim developed condition which allows for gravity drainage via the riser and outlet pipe. Total basin storage volume to elevation 33.0 msl is 8.47 acre feet from flow line of spillway to basin bottom. The westerly desilting basin has been designed for a 1,000-year, 24-hour storm event The tributary drainage area to the western basin is limited at this time based on the existing low area to the east of WMU FU-03 cell. As the former Austin Road Landfill area is developed, permitted channel/ditches will be constructed to convey storm water to the westerly desilting basin. The basin has been designed to collect fine sand to coarse silt particle size. The basin has a storage capacity of 13,660 cubic yards. The outfall pipe has a flow capacity of 82 cfs minimum (capacity will increase as head increases) and the spillway has a capacity of approximately 300 cfs. As further development of the landfill occurs, additional basin capacity for detention can be made by excavating the basin and installing storm water pumps. Detention volumes of up to 35.3 acre feet can be obtained by lowering the bottom of the basin to 10 ms], which is approximately 13 feet above ground water. Hydrology and hydraulic calculation information for the entire Forward Landfill was obtained form the Joint Technical Document (JTD) (BAS et al, 2001). Specific hydrology and hydraulic calculations for the inlet trapezoidal channel, basin, basin spillway, and outlet pipe are included in Appendix B. FORWARD LANDFILL WMU F-03 AND F-WEST DESIGN REPORT 4-1