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