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2.05 APPLICATION FOR PERMIT FOR SURFACE OR UNDERGROUND MINING ACTIVITIES - MINIMUM <br />REQUIREMENTS FOR OPERATION AND RECLAMATION PLANS. <br />The emergency spillways of Pond Nos. 1 through 4 will safely discharge run -off <br />from a 100 year precipitation event, with the spillways flowing at a 3 -foot depth, <br />leaving one foot freeboard to the top of the dam. For calculations of spillway <br />capacity and apron design see Ponds, Impoundments, and Dams Appendix in <br />Volume 8A. <br />The steel bin wall construction lends itself to minimal settlement. The bottom of <br />the bin wall dam was constructed on original ground, minimizing the consolida- <br />tion of soil beneath the dam, thereby limiting settlement. The backfill within the <br />bin walls does settle but maybe refilled during the periodic maintenance <br />program. The dam height has not been raised over design height because of <br />the minimal settlement. <br />The bin wall dam construction is not of an embankment nature. The bins are <br />12 feet wide. The dam is 14 feet high. The structure does not have any slope <br />embankments, due to the bin wall construction. Vegetative and organic matter <br />was removed before the dam was constructed. All fill material used within the <br />bin walls is free of sod, roots, and other vegetative matter, frozen soil and coal - <br />development waste. Please refer to Construction Specifications within the <br />Ponds, Impoundments, and Dams Appendix in Volume 8A for specific detail on <br />placement of fill. The backfill was placed in 4-6 inch layers and compacted <br />using power tampers. It was compacted to approximately 90% of maximum dry <br />density. <br />Sedimentation Pond - Timber Storage Area a.ka. Run -of Mine Area <br />One sedimentation pond is located immediately downstream and east of the <br />timber storage area. It is located in the NW %NW' /4 of Section 25, T.13.S., <br />R.92.W., 6th P.M. <br />Drainage ditches have been installed to intercept surface runoff from the timber <br />storage area and direct it to the sedimentation pond. <br />The dam is constructed using compacted earth fill. Plans and specification are <br />as shown in Ponds, Impoundments, and Dams Appendix in Volume 8A. The <br />pond was constructed during April, 1978. <br />The dam is an existing structure and is located immediately downstream of the <br />timber storage area. It conforms to 4.05.2, .5, .6, .7 and .17. It is not located <br />within any stream channel and discharge, if any, drains into Steven's Gulch. <br />The sediment volume and 10 -vr., 24-hr. inflow is calculated in the Ponds, <br />Impoundments, and Dams Appendix in Volume 8A. The sediment volume is <br />0.27 ac -ft . and the 10-yr, 24 -hr. inflow is 0.37 acre feet. The total required is <br />0.27 + 0.37 = 0.64 ac -ft. <br />This pond is equipped with a conduit de- watering device as shown on Map No. <br />8A -3. Sediment volumes are monitored and cleaned following the Mine <br />Sediment Monitoring Program. <br />TR -58 ® y - 21 - 03/14 <br />G%Ja) •2VH <br />