Laserfiche WebLink
In the D-Portal Area, diversion ditches will be constructed to route run-off <br />from undisturbed areas away from disturbed sites and directly into the natural <br />drainage system. Collector ditches will be installed to intercept run-off from <br />structures and stockpiles in the D-Portal Area and to route that run-off into a <br />sediment pond. The ditches were designed using the same criteria as those in <br />the Refuse Disposal Area. <br />The diversion and collector ditches will be maintained and operated until the <br />permit area has been restored and revegetated. After reclamation has been <br />deemed complete by the regulatory agencies, these structures will be reclaimed. <br />A 2,750-foot diversion will route Scullion Gulch entirely beneath the D-Portal <br />area. This accomplishes two purposes: it provides additional area for the con- <br />struction of surface facilities, parking, and portals; and reduces the number <br />1 <br />of required sediment ponds since' the stream is effectively routed away from <br />disturbed areas. The diversion will be constructed of asphalt-coated corrugat- <br />ed metal pipe. As three lateral culverts will add additional discharge along <br />the main diversion, the pipe diameter will increase from 96 inches at the inlet <br />to 108 inches under the fill and to 120 inches at the outlet. At the inlet, <br />which is immediately upstream of the refuse haulroad, the pipe will be draining <br />4,653 acres. The three laterals consist of 72-inch, 42-inch and 36-inch pipes, <br />draining 234, 42 and 17 acres, respectively. The diversion was designed to <br />carry flow from a 100 year-~4:hou r. precipitation event. Calculations using <br />methodology presented in Chapter 21, Section 4, SCS National Engineering Hand- <br />book and SCS-TP 149 indicate that flow from the 100 year-24 hour precipitation <br />event at the inlet will reach 503 cfs at the inlet, the laterals will add 351 <br />.cfs, and discharge at the outlet immediately below the D-Portal sediment pond <br />will Abe 854 cfs. <br /> <br />Design calculations included within the permit application demonstrated that <br />503 cfs will pass through the 96-inch diameter pipe entrance with a headwater <br />depth of 9.6 feet. Riprap will be placed at the inlet and outlet of the diver- <br />sion, and concrete wingwall-type headwalls will be installed at the inlets. <br />Mine Dewatering <br />Although groundwater inflow into the mine is expected to be very low, the ap- <br />7 <br />