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5-8 5.2.5 Fill Phasing The fill phasing plan is shown on Drawing 7. This plan is conceptual and actual phasing direction may vary. It is anticipated that each major phase of development depicted in Drawing 7 will consist of smaller fill sequences. Class II and III waste is currently being accepted at WMU FU -08 (northern portion) (within Phase 8 in Drawing 7). WMU FU -10 is located south of FU -08 and is Phase 8. Phases 3 through 7 were constructed (from west to east) to the south of and over the Austin Road Unit within an existing borrow area. The existing scalehouse facilities will be relocated easterly adjacent to the site offices during fill sequencing for Phase. The future scales/scalehouse facilities will serve Phase 8 located in the northeast corner of the site and Phase 9 which will close the gap between the two existing landfill prisms. Phase 9 fill sequencing will proceed from west to east over Phases 8 and 2. Phase 10, located south of the South Branch, will be the final fill sequence. To mitigate existing infiltration concerns, an interim final cover will be placed over the Austin Road Unit (see Section 5.2.2.3). 5.2.6 Drainage Control System The primary function of the surface water drainage and erosion control is to minimize erosion, convey surface waters around the refuse cells and off the landfill in order to minimize potential infiltration of surface water into the refuse prism as further discussed in Section 7.6. The surface drainage plan for the Forward Landfill is shown on Drawing 8 and drainage details are shown on Drawing 9. The drainage control facilities include a network of top deck diversion berms and inlets, downdrains, bench ditches, perimeter channels and stormwater sedimentation basins/detention basins. A description of the drainage facilities are discussed in the following sections. 5.2.6.1 On -Site Drainage Control Permanent storm water runoff and drainage control facilities on site were designed to carry the peak discharge resulting from a 1,000 -year, 24-hour storm event, as required by 27 CCR, Section 20320 for a Class II waste management unit. A discussion of the drainage system design calculations is presented in Section 7.6. The drainage network for the completed landfill is designed to carry storm water at velocities that will control run-off and minimize erosion. The landfill's drainage control plan is shown on Drawing 8 and details for the surface water drainage control plan are shown on Drawing 9. The final landfill grades are designed so that surface water will run off the landfill via sheet flow until it is intercepted by a deck berm or bench ditch. The bench ditches subsequently drain toward downdrains or corrugated steel pipes, which discharge to perimeter channels. Finally, the perimeter channels drain to one of Forward Landfill SWT Engineering Joint Technical Document - April 2014 z:\projects\allied waste\forward\five year permit rvw 2013\1td-5 yr pr 2013\text\sec 5_final.doc