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1 ''y .. Revised December, 1995 The location of all existing and planned sedimentation ponds are presented on the Hydrology - South Map (Map 12) and the Hydrology - North Map (Map 11). The design plans and specifications for the sedimentation ponds are described in this section. The design parameters and detailed sedimentation calculations for the sedimentation ponds are shown in Exhibit 7, Hydrology Information. The sedimentation pond embankment and emergency spillway design are also shown in Exhibit 7, Hydrology Information. All sedimentation ponds will be located as close as practical to the areas to be disturbed. Other methods of sediment control will be located on the reclaimed areas; these methods include the use of contour furrowing, terraces, and chisel plowing. This application contains calculations used to determine runoff volumes and " flow rates for a theoretical 10-year, 24-hour precipitation event and subsequent sediment volumes. The precipitation data were obtained from the NOA Atlas 2, volume 3 for Colorado; soil types were obtained from the Soil Conservation Service, and are shown on the Soils - South Map (Map 6) and the Soils - North Map (Map 5). Although the mining activities within each watershed of the permit area will create changing hydrologic conditions, the initial design models are generally based on a theoretical, short-lived, worst case scenario. The worst case scenario is predicted to exist during and just after initial topsoil removal operations but before any mining excavations have begun. In terms of ground water, Colowyo's pits are essentially dry. Pumping of pits due to collection of surface runoff is anticipated only on an extremely rare occasion, is performed mainly for safety purposes, and will not effect the design or function of the sedimentation ponds. Sediment will be removed from all sedimentation ponds when the volume of sediment accumulates to 60 percent of the designed sediment storage volume, or to a volume that will not allow effective treatment of the runoff and sediment that would result from the 10-year, 24-hour precipitation event. Survey measurements of sediment accumulations will be conducted bi-annually for discharge points 003, 004, and 007 and any new sediment ponds and every third year for 001, 002, 005, and 006. Ponds will be dredged when water levels are lowest, and the least amount of precipitation is expected. The removed sediment will be used as topsoil or subsoil if it meets the suitability criteria discussed under Section 2.04.9. The Division will be notified of this determination if the material is selected overburden material that can be substituted for as a supplement to topsoil. All ponds will be designed so that the minimum elevation at the top of the settled embankment is at least one foot above the elevation of the water