2015-06-22_PERMIT FILE - C1996083 (2)

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• requirement by Rule 4.05.6(11)(f), a stability analysis was performed to verify stability. The results show that the slope should be stable, and therefore acceptable. The stability analysis is presented in Section 4.3.3. The embankment will be constructed of clean, locally available borrow material, produced by the central ridge removal or the sediment pond excavation. The foundation of the embankment should be stripped and scarified before construction to assure a good contact with the first embankment lift. A cutoff trench constructed in the foundation on the embankment centerline should be excavated three feet wide by three feet deep. This trench will be filled and compacted with the same materials and compaction effort as the embankment materials. It will provide a barrier to seepage along the foundation contact. The embankment materials should be compacted to 95 percent Standard Proctor compaction (D- 698, or AASHTO T-991, and should be checked frequently in the field during construction. Materials should be placed in 8-inch maximum lifts, with removal of rock sizes large enough to interfere with lift placement. Upstream and downstream embankment faces should be stabilized with grass or other thick vegetation. This will protect the slope from rain erosion • and infrequent pools. Small fetch distances resulting in insignificant wave run-up during maximum pool events are not a design factor. 4.2.5 Sediment Pond Dewatedng The sediment pond will be dewatered using two methods. The first method is the primary dewatering system. This system is an eight inch steel outlet pipe, placed as shown on Drawing 95266-04. An eight-inch diameter pipe was selected to dewater the pond rapidly if needed, and to ensure that it will not clog when used. The pipe intake will be at EI. 5,975 ft, just above maximum elevation of sediment produced by the 10-year, 24-hour storm. The intake should be constructed as shown in Drawing 95266-04 ,with an elbow down to prohibit the accumulation of water in the pipe, and discourage freezing and thawing that may damage the gate valve. The manual gate valve can be placed on the downstream side of the embankment and will control flow through the outlet pipe. Agate valve on the downstream side of the embankment provides for ease of operation, but the valve installed on the upstream side of the embankment is optimum if it can be controlled at the crest. Pipes after the gate valve will take discharge water down to the Highway 133 runoff ditch so erosion of • the existing roadway cut will be avoided. The downstream outlet pipe should be secured by 96266/1424.RPT Coel Mine Waste Bank Finel Design for the Bowie No. 2 Mine June 1996 W E S T E C weQuACr-or 18