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• Phases 3 through 7 will be constructed (from west to east) to the south of and over the existing Austin Road Landfill within an existing borrow area. The existing scalehouse facilities will be relocated easterly near the existing site offices during fill sequencing for Phase 7. 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 at the south side of the South Branch will be the final fill sequence. 5.2.6 DRAINAGE Surface water control includes protection of the landfill from surface water run-on and flood influence by Little Johns Creek as well as proper handling of surface water runoff from the landfill areas. The surface drainage plan for the Forward Landfill is shown on Drawing 9 and drainage details are shown on Drawing 7. The drainage control facilities include a network of top deck diversion berms and inlets, down drains, perimeter channels • and bench drains for managing surface water runoff. A brief 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 design calculations is presented in Section 5.3.5. The drainage network for the completed landfill is designed to carry storm water at velocities that will control run-off and minimize erosion. The Forward Landfill surface water control plan consists of an integrated system of bench ditches, perimeter channels, top deck perimeter berms, and storm water sedimentation basins (shown on Drawings 7 and 9). The final landfill grades are designed so that surface water will run off the landfill via sheet flow until intercepted by a deck berm or bench ditch. The bench ditches subsequently drain toward trapezoidal AC down drains or corrugated steel pipes which discharge to perimeter channels. Finally, the perimeter channels drain to a stormwater • sedimentation basin. Forward Landfill)TD 5-9 L:\Allied\2000.193\Reports\td:Sec-5.0:05/24/02 BRYAN A.STIRRAT 6 ASSOCIATES