1991-09-26_REVISION - C1981035 (3)

Home Browse Search

� t 1. Scope and Purpose This Technical Revision is an update to TR2 dated May 1991. Although significant changes have been made much of this document relies on information in TR2. The major change in this document is a new drainage plan which diverts water from upstream areas around the mines site. This results in a reduction in the required size for the sedimentation ponds. A pipe and channel drain system is proposed to accomplish this diversion. New hydrologic analyses based on the redefined subbasins are presented. Drainage features such as, pipes, sediment ponds and outlet works are resized using the new hydrology. 2. Mine Drainage Plan The drainage plan for the National King Coal Mine will consist of diversion of uncontaminated water originating upstream of the mine yard, through the yard to the discharge point at the north end of site. Runoff generated on the yard itself as well as runoff form two small natural areas adjacent to the yard will be collected and routed through the sedimentation ponds. Diversion of Uncontaminated Runoff A schematic diagram of the mine site showing the drainage features is given in figure 1. Runoff in the eastside channel is intercepted above the coal waste pile at a diversion intake structure. This flow will enter a buried pipe and travel through reach 1 to its junction with an existing buried pipe(reach 2). Runoff from the hillslope on the north side of reach 1 will be intercepted by a ditch located just above the bottom of the waste pile. This drainage ditch will flow to the west and will enter a pipe which is joined with the existing reach 2 pipe at the pipe/channel junction shown in figure 1. The flow will travel through the existing pipe (reach 2) down the embankment where it will be joined with new pipe laid in the existing channel and buried. This section (reach 3) will be extended downstream to a junction with the westside drain pipe. From this junction, reach 4 will extend downstream to its terminus shown in the figure. At this point the flow will enter an open channel and flow the remaining distance to the discharge point in the field at the north east end of the site. The westside drain consists of the existing diversion at the mouth of the canyon drainage where the flow enters an existing pipe, reach 5, and travels to a point under the conveyor. From this location a new line will be laid which will extend the drain across the yard (reach 6) to its junction with the eastside drainpipe.