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The site and pad will have a minimum of a 1 percent slope and Windrows will be con- structed normal to the slope, so there will be no standing water on the pad. Detailed design calculations are presented in Appendix 1. 7. Surface Drainage Plans Include a schematic drawing of surface drainage plans showing all berms, down- drain systems, stormdrain systems, the location and direction of flow in perimeter drainage channels and off-site discharge points for runoff water. The grading plan shows the proposed grading of the site. The grading plan is the same for all of the potential composting options. A 1-percent minimum grade is provided at all points in the composting site. The composting Windrows are arranged normal to the site slope to allow free drainage and minimize ponding. The site is sloped to drain to two ditches designed to carry the water from the 25-year 10-minute duration storm (0.25 inches, 1.5 inches per hour) assuming all the water that falls on the composting site runs off. The ditches will carry the water to a retention pond designed to hold the net average annual rainfall during months where rainfall exceeds evap- oration (5.67 inches) assuming all the water that falls on the site runs off. This exceeds the 25-year, 24-hour rainfall event (2.28 inches). All surface water runoff from the Compost Facility will be collected and stored in the retention pond. Collected runoff that has not contacted any waste, or has contacted waste but meets the water quality criteria for storm water discharges, is either discharged to the South Fork, used to add water to the initial compost mixture to provide the desired initial moisture content, or evaporated. All collected runoff which does not meet the water qual- ity criteria for stormwater discharge will be either pumped into the leachate evaporation pond located in Interim WMU F, or hauled to a wastewater treatment facility for treatment. 8. Drainage g Control Indicate on a map the locations of primary drains, berms, etc. Provide a description of all surface and subsurface drains, which are to be used to control water from areas on, or adjacent to the composting site including the types of protective dikes, berms, and levees planned for this facility. In addition, please sped how the site will be designed and constructed to limit ponding, infiltration, inundation, washout, etc. Runon to the composting site is prevented by an existing berm located on the eastern and a portion of the south edges of the site. Site slopes generally decrease from the northeast to the southwest. An existing ditch prevents runon from the south. The South Fork of Little- johns Creek prevents runon from the north. w&10029M4.wp5/32 9/28/94 32