PERMFILE128459 - Laserfiche WebLink

Home Browse Search

• 36 best represent the disturbed area and are given below: Hydraulic conductivity ~ 1.0 inch per hour Porosity ~ 0.40 initial saturation ~ 0.65 Final saturation ~ 0.90 Capillary suction head ~ 1.0 inch , The resulting runoff from the design storm is 0.060 acre-feet per acre. Table 8 lists the area of each internal drainage, thr runoff volume, and the depression storage except for Area I, the mine pit. The area contributing run- off to the mine pit is approximately equal to the surface area of the pit, ~. however, the pit is well over 20 feet deep and has more than enough depression storage. All areas have at least twice as much depression storage as required r to crontain the 10-year runoff except Area IV which has the capacity for one ' and one-half times the 10-year runoff volume. Thus, no runoff was considered from these areas for the present-mining condition. Special consideration should be given to the haul road drainage within the mine area. The regulations do not require passage of roadway drainage through sediment pond structures; however, some drainage from disturbed areas does flow to the haul road at the mine area and should be kept from flowing to the natural drainage (Magpie Creek diversion). Also, where the haul road run- off enters the Magpie Creek diversion it runs downs the steep roadway embankment for about 40 feet and causes severe gully erosion down the embankment to a point where the road is ao longer usable. This condition can best be controlled by regrading the haul road so that the runoff enters the pit area. Small side chan- nels along the east side of the haul road (see Hydrology Map 2, Appendix A) will also help provide adequate control of this drainage. These side channels can be triangular in shape with 2:1 side slopes and they should have a minimum depth of one foot. Design of these channels is disucessed in Section 6.4 6.2 Culvert Evaluation There are two existing culverts within the G.E.C. permit boundary. One is on Newlin Creek under the haul road and the other is at the Magpie Creek . diversion outlet. Also, there is possible requirement for a culvert on the outlet of Sw-10 under the haul road. Discussion on the need for this culvert is given later in this section.