2007-10-30_PERMIT FILE - C1982057 (2)

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SPILLWAYS The sediment pond has two spillways; a nonclogging principal spillway and an emergency spillway. See Exhibit 13-5A for spillway locations. The principal spillway consists of a 24-inch diameter drop inlet CMP riser with a trash rack at the inlet. This pipe will be keep the pond water level at 6,872.2 elevation. Maximum estimated elevation (peak stage) above the principal spillway from inflow from the 10-year, 24-hour event will be 6,872.5. This is 1.6 feet below the emergency spillway invert elevation and demonstrates that no flow will pass through the emergency spillway in accordance with Rule 4.05.9 (2) (b) . The embankment portion of the emergency spillway consists of a trapezoidal channel as shown on Exhibit 13-5A. Assuming the principal spillway was plugged, the trapezoidal channel can safely pass the runoff from the 25-year and 100-year, 24-hour storm events. The emergency spillway outflow channel is a rock riprapped trapezoidal channel (see Addendum 13-3-D for design specifications). The peak stage elevation from runoff from the 100-year storm is 6,874.9. This elevation is 4.7 feet below the top of embankment. This demonstrates that Pond 005 is constructed and operated in compliance with Rule 4.05.9 (2) (c) (iii) . SUMMARY The capacity of Pond 005 is attributed partially to the embankment and partially to the pond excavation. During passage of the 10-year, 24-hour storm the effluent settleable solids concentration is less than the receiving stream water quality standards, and there is no flow through the emergency spillway. In addition, the emergency spillway is designed and constructed to safely discharge the 25-year and 100-year, 24-hour storm events. The embankment was constructed to be stable and provide adequate freeboard. Therefore, based on the design and as constructed and operated, this structure complies with the appropriate regulations for a sedimentation structure. A toe drain and horizontal drainage system was constructed to collect any seepage and discharge below the embankment. A 4-inch PVC dewatering pipe was also installed. SCC will periodically inspect the structure for sediment storage, structural integrity, and hazardous conditions. Maintenance and remedial work will be performed in accordance with the approved mine permit. STABLITY MONITORING According to the Amuedo and Ivey report regarding the pond stability, and the geotechnical investigations presented in Ground Engineering's report, the majority of the pond structure is located on stable ground. As an added measure of safety, stability monitor monuments were installed at the pond as located on Exhibit 13-5A. There monuments will be surveyed quarterly (weather TR-59 13-3C-7 Revised 08/07