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4.0 Hydrology <br />• Peak discharges, volumes, pipe sizes, ditch sizes, and other hydrau]ic structures were <br />calculated with the following storm events: l0yr-24hr event is 2.20 inches, the 25yr-24hr <br />event is 2.60 inches, and the 100yr-24hr event is 3.20 inches. This storm event <br />information was taken from first page of Exhibit 8 of the existing mining permit for the <br />King Coal Mine. <br />5.0 Sediment Pond <br />The sediment pond was designed to contain and treat the volume from a l0yr-24hr event. <br />The runoff from this l0yr-24hr event would be 1.76 acre-feet, refer to Appendix C, <br />Sediment Pond With Principal Spillway. The emergency spillway will handle a ZSyr- <br />24hr event, 2.35 acre-feet, refer to Appendix C, Sediment Pond With Emergency <br />Spillway. There is sufficient capacity above the recommended sediment level to contain <br />a l0yr-24hr event without overflowing the principal spillway. These capacities are also <br />shown in Figure 3, Sediment Pond Capacity Curve and Table 2, Sediment Pond Capacity. <br />5.1 Watershed Sediment Yield <br />Particle size distribution for the King II Mine was selected from Table 3.1 in the "Design <br />Manual for Sedimentation Control through Sedimentation Ponds and Other <br />PhysicaUChemical Treatment", by Simons, Li & Associates, Inc., 1982, prepared for the <br />U. S. Office of Surface Mining. Soil type was determined from the map titled King II- <br />006 -Soils, Vegetation & Land Use in Tab I S of the permit application. This particle <br />size distribution was used in the SEDCAD 4 program for the prediction of sediment <br />accumulations in the sediment pond. Results of the sedimentology runs are shown with <br />the principal and emergency spillway results in Appendix C. The maximum sediment <br />allowed in the sediment pond would be 2.188 acre-feet at an elevation of 7232 feet, refer <br />to Figure 3, Sediment Pond Capacity Curve. The sediment would have to be removed <br />when it reaches 60 percent of this amount. <br />Using the sediment numbers from a IOyr-24hr event, 132 tons of sediment would be <br />deposited in the pond. Assuming an average density of 110 lbs/ft' it would take <br />approximately 39 storms to fill the pond to the proposed sediment level of 7232 feet. The <br />pond has a capacity to handle 28-25yr-24hr storms to get to the same level. This is based <br />on the assumption that 185.3 tons of sediment are deposited each storm. <br />L J <br />National King Coal, LLC. <br />King Mine /I <br />Apri12006 <br />Page S <br />