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SEDIMENTATION POND N0. 5 General Design Sedimentation Pond No. 5 is designed to contain the surface runoff and sediment load accumulated during the 10-year, 24-hour event from the drainage area shown on the Drainage and Sediment Control Map, (Map 20). The watershed consists of the drainage area collected by the access road collection ditch, Sediment Collection Ditch No. 1 (CD-1), and the mine facilities area not draining to Sedimentation Pond No. 1. The facilities area surface runoff is collected at the yard area catchment basin and routed via a 24-inch CMP to the access road collection ditch which drains to Pond No. 5, as shown on the Drainage and Sediment Control Map, (Map 20). Pond No. 5 employs a ripraped trapezoidal channel as an Emergency Spillway. The outlet structure is designed to safely pass the peak • discharge from the 25-year, 24-hour storm event. Available freeboard during the 25-year, 24-hour storm event exceeds one (1) foot. Pond No. 5 utilizes a 24- inch CMP with a 12-inch diameter gated inlet for dewatering purposes. Dewatering is performed to insure that adequate design storm storage capacity exists shortly after each storm in case a subsequent storm event occurs. Dewatering is performed only after 24 to 36 hours of detention time is achieved to allow for settling of suspended solids. Refer to Table 10, Sedimentation Pond No. 5 - Design Summary, for design results. The watershed boundary for Sedimentation Pond No. 5 is shown on the Drainage and Sediment Control Map, (Map 20). The design drawings and stage/storage curve are shown on the Sedimentation Pond No. 5 Design Map, (Map 24). The stage/storage curve illustrates the pond's available sediment and runoff storage volume. Support calculations utilized in the pond's design are contained below in the following text of this exhibit. ~~ 74 R Revised - September, 1991