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. "greater than a 100-year flood precipitation event" the south bank of the North Fork would <br />experience more damage from the river itself than from overtopping the ponds. Furthermore, the <br />facilities on the south bank aze above the floodplain elevation and should experience minimal <br />damage. <br />Collection and Diversion Channels <br />Cross Section <br />The cross-section of a typical collection and diversion channel is shown in Exhibit 47 and the <br />minimum ditch designs are shown in Exhibit 66. Exhibit 66 discusses the hydrologic design of <br />ponds, channels, and culverts in the area of the surface facilities, including the Sylvester Gulch <br />Facilities Area. The locations of the culverts used for collection and outfall may be found on the <br />Plot Plans showing Hydrologic Structures in Exhibit 43 and drawings in pertinent Appendices. <br />The hydrologic design of the RPE pond is located in Exhibit 70 and Exhibit 66. <br />Desitn Dimensions <br />The hydrologic criteria of the diversion and collection channels, are located in Exhibit 66. <br />Exhibit 46, Exhibit 47, Exhibit 49, Exhibit 66, and Exhibit 70 contains all the construction <br />specifications for Ponds M$-1 through MB-5, the SG-1 pond, and the RPE pond (note that MB- <br />2 has been redesigned and is included in Exhibit 66 as MB-2R, and pond MB-6 no longer exists). <br />The designs for the trash racks that may be installed on some culverts, 30 inches or less <br />minimum cross-sectional dimension are in Exhibit 43. Acreages of drainage azeas relating to <br />certain diversion and collection channels are shown in Exhibit 66. <br />Culverts <br />Locations of culverts aze shown on Map 54, Map 54A, and Map 54B. Details and the culvert <br />specifications are found in Exhibit 66. Details and culvert specifications for the ditches and <br />culverts at the RPE area aze found in Exhibit 70 and Exhibit 66. <br />MCC may install "internal" culverts (i.e., located within the mine site drainage systems) to <br />provide access. If added, the culverts would be sized equivalent to or greater than the next <br />downstream ditch or culvert. <br />Sedimentation Ponds <br />Prior to the disturbance of the azea for surface construction at West Elk Mine, four sedimentation <br />ponds and associated collection structures were constructed to effectively retain runoff from the <br />area to be disturbed. The other ponds were developed prior to the use of the old Bear Mine azea; <br />construction of the Lower Refuse Pile, formerly referred to as the U.S. Steel laydown area; <br />construction of the Sylvester Gulch Facilities azea; and construction of the RPE area. <br />Prior to construction, topsoil was salvaged from all construction areas, stockpiled, and/or applied <br />to slopes and cuts as necessary for reclamation. Exterior slopes of sedimentation ponds at the <br />2.05-38 Revised November 2004 PRIG; Rev. Minch 1006; Rev. Apri11006 PRI G; Rev. May 1006 PRIO <br />