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• 4. Provide anon-clogging dewatering device and principal spillway that will provide <br />adequate detention time for the 10-year, 24-hour storm event and scill allow a <br />method to dewater the pond in a reasonable amount of time. <br />In some instances, mining will cause the drainage area to change during the life of the <br />sedimentation structure. When the pit moves into the watershed, runoff is intercepted by <br />the pit. In these cases, a conservative procedure was used; the structure was analyzed for <br />the largest anticipated disturbed drainage area that will contribute runoff to the structure. <br />It was estimated that this condition would occur if all of the proposed mining area is <br />disturbed and the area is in different phases of mining and reclamation. In addition, the <br />structure was conservatively designed to include adequate capacity for sediment storage <br />and to treat the runoff from a 10-year, 24-hour precipitation event. Finally, the pond was <br />constructed to safely pass the peak discharge from 25-year, 24-hour precipitation event <br />and provides adequate freeboard to prevent overtopping of the embankment. The <br />SEDCAD output for the pond as-built conditions are presented in Addendum 13-SH-A, <br />13-SH-B, and 13-SH-C. <br />• Summarv <br />The capacity of Sedimentation Pond 017 is attributed partially to the embankment and <br />partially to the pond excavation. During passage of the 10-year, 24-hour storm the pond <br />is designed to effectively treat the runoff and will not discharge flow through the <br />emergency spillway. In addition, the emergency spillway was designed and constructed to <br />safely discharge the 25-year, 24-hour storm event. <br />The embankment was constructed to be stable and provide adequate freeboard. <br />Therefore, based on the design, this structure complies with the appropriate regulations <br />for a sedimentation structure. SCC will periodically inspect the structure for sediment <br />storage, structural integrity, and hazardous conditions. Maintenance and remedial work <br />will be performed in accordance with the approved mine permit. <br />LJ <br />Construction Summary <br />13-5H-2 <br />