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n U LJ All but two sediment ponds are designed to contain the runoff and sediment from a 10 year, 24 hour precipitation event. Sediment Ponds 1 and 2 are being combined to contain a 25 year, 24 hour event in lieu of two spillways or an open channel spillway. Spillways or overflow devices are designed to carry the runoff from a 25 year, 24 hour precipitation event. Collection ditches and diversions associated with the refuse piles are designed for 100 year, 24 hour precipitation events and all other collection ditches and diversions, unless otherwise noted, are designed for 10 year, 24 hour precipitation events. Permanent stream channel diversions are designed for 100 year, 24 hour precipitation events. The cross-sectional area of each is designed to discharge peak runoff at adequate velocities to reduce adverse erosional effects. In areas where excessive erosion is expected, rip-rap or other types of energy dissipators will be used to line the ditch. All sediment ponds or impoundments within the permit area are designed for a capacity of less than 1000 acre-feet and have no embankments in excess of 10 feet in vertical height from the bottom of the spillway. None have a surface area at high water line in excess of 20 acres. All sediment ponds are located within disturbed areas, and out of the course of perennial streams. The ponds are designed to provide adequate sediment storage volume and access for periodic sediment removal. Sediment storage volumes are based on the Universal Soil Loss Equation. The ponds are designed to provide anon-clogging dewatering device or conduit spillway that is not located at a lower elevation than the maximum sediment storage level. Ponds are designed to provide an appropriate combination of principal and emergency spillways to safety discharge the runoff from a 25-year, 24-hour precipitation event. Ponds are designed to prevent outflow through the emergency spillway during the containment of runoff resulting from a single 10-year, 24-hour precipitation event. Water accumulations in the pond above the maximum sediment level will be held until adequate settling has occurred to meet discharge limits of Total Suspended Solids. • 13-6 (Rev. 12/02)