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• 1. Scope and Purpose <br />In compliance with Colorado State reclamation regulations pertaining to hydrology of <br />mine sites, a design for the drainage system at National King Coal Mine in presented in <br />this document. Detailed hydrologic and hydraulic analysis of sedimentation ponds, <br />channels and pipes were performed as part of this study. <br />2. Mine Drainage Plan <br />The drainage plan for the National King Coal Mine has two components: 1) diversion <br />of uncontaminated water, originating upstream of the mine yard and waste pile, around <br />the yard to the discharge point at the north end of the site and 2) routing of water from <br />the mine yard, waste pile and some adjacent areas through sedimentation ponds. This is <br />achieved through a series of open channels and pipes. Figure 1 is a schematic diagram <br />of the drainage basin which shows the different subbasins. The large areas labeled east <br />and west basins are diverted around the mine. The area labeled mine yard (this includes <br />the waste pile) is the only area which generates contaminated runoff. The natural areas <br />adjacent to the mine yard on the west, as well as the natural area south of the waste pile <br />do not generate contaminated water but are routed to the sedimentation ponds in order <br />to simplify the drainage system. <br />2.1 Diversion of Uncontaminated Runoff <br />• Runoff from the east basin is intercepted above the coal waste pile in an open <br />channel and routed through reach 1 as shown in Figure 2. Reach 1 terminates at a <br />junction with an armored open channel at the front and on top of the waste pile, <br />designated reach 2. This channel carries the uncontaminated runoff down the waste pile <br />face and to the clear water diversion channel behind the office, reach 5. <br />Because of the high flow velocity exiting the pipe, energy dissipation at the outlet is <br />required. Water from the channel will discharge into a rock lined pool 5 ft wide by 10 <br />feet long with a minimum depth of 3 ft before entering the downstream channel. The <br />outlet from the pool to the ditch should be at the same elevation as the invert of the <br />channel outlet. The rack lining should consist of two layers. The bottom layer should be <br />a'/." to 2" gravel blanket at least 3" thick. This wi11 prevent the erosion of soil from the <br />pool floor and sides due to surging flows. The second layer should be a graded material <br />with a minimum stone size of 8" and a D~ of 14°. The outer rock lining should be at least <br />two stones thick. This layer will resist the high velocity flow exiting the pipe. The <br />channel exit should be directed, at an angle toward the center and bottom of the pool. <br />Care should be taken to place large stones in the path of the exiting jet. As an <br />alternative the pool can be constructed with rock filled gabions. In either case the rock <br />protection should extent one foot above the pool outlet opening elevation. <br /> <br />January 1998 <br />