1988-04-18_PERMIT FILE - C1981008A

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effort to be conservative, Peabody will use the largest soil erodibility factor of 0.32 at this time for design purposes (see Table 3) . Length - Slope Factors (L,S) Length and Slope Factors for each subwatershed were determined by measuring representative overland flow paths on topo maps within the subwatershed and taking an average of these measurements. As a general rule, lengths varied from 200 feet to 800 feet and slopes from 3 percent to 12 percent. Control Practice Factor (CP) The control practice factor for most soils and vegetation cover combinations ranges from 0.10 to 0.90. Again, in an effort to be conservative, Peabody will use 1.0 as the control practice factor on all subwatersheds at this time. Particle Size Distributions The particle size distribution for this sediment pond was taken from Simons, Li and Associates (Design of Sediment Control Measures for Small Areas in Surface Coal Mining) . This distribution is representative of a sandy loam soil similar to those described in Tab 9 of the current Nucla Mine Plan. The specific gravity of the soil and the submerged bulk specific gravity were estimated based on the references cited above. STORAGE CAPACITY The storage capacity of Sediment Pond 001 was also analyzed using the SEDIMOT II computer program. The capacity of this pond was designed to provide storage for the runoff entering the pond as the result of a 10-year, 24-hour precipitation event plus the inflow from potential pit pumpage while maintaining a minimum of 0.5-feet of freeboard from the emergency spillway elevation. This design also includes a minimum storage volume for sediment. When periodic sediment surveys of this pond indicate one or less 10-year, 24-hour MUSLE sediment storage availability, the pond will be dewatered and the accumulated sediment removed. Table 4 is a summary of the designed storage capacity. 7