2001-12-11_PERMIT FILE - C1982056A (5)

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Peak flow into the pond would be 2.67 cfs if both pumps were pumping at their maximum rates. After the underground workings are pumped down, approximately mid 2001, the anticipated flow would be about .18 cfs (90 • gpm). The effluent detention time will depend upon the flow through the system plus the amount of sodium hydroxide injected into it. Diversion Ditches All diversion ditches are designed to carry runoff from the 10-year, 24-hour precipitation event to the sedimentation ponds. The predicted runoff rates, carrying capacity and ditch size are given in the appropriate "TABS". Culverts The culverts utilized in the sediment conVOl plans are shown on Map 24, Surface Facilities, at the Foidel Creek Mine. All of the culverts are wrrugated metal pipe (CMP), with the exception of two schedule 80 steel pipes. These steel pipes are used for operational convenience at the mine portal area. Flow capacities and sizes for the culverts are given in the appropriate `°TAB". Sedimentation Ponds (Ponds D, E, F, and G) Pond D receives water from diversion Ditches D-1, lower section of D-2, and D-3, and D-4. The amount of inflow from Ditch D-l to Pond during a 10-year, 24-hour event is calculated to be 7.6 acre-feet. The average rate of inflow from the Area 2 Pit under base floev conditions is approximately 0.5 acre-feet. Calculated additional inflow from Ditch D-3 during the 10-year, 24-hour precipitation event is 12.3 acre-feet. The emergency spillway of Pond D is designed to handle the peak flow rate from the 100-year, 24-hour storm event. This requirement is based upon the pond meeting the MSHA size criteria. Pond E was relocated in conjunction with expansion of the coal stockpile area. Relocation involved removal and placement of up to 13,100 cubic yards of topsoil and subsoil material from the new pond location and placed in the stockpiles shown on figure IlC excavation of any potentially deleterious materials and scarification of the .embankment foundation area, and controlled placement and compaction of embankment fill material. The relocated pond receives disturbed are runoff via Ditches E-1, E-2, and E-3, as well as direct surface runoff from a portion of the coal stockpile area and the preparation plant facilities area north of the overland conveyor. For the 10-year, 24-hour event, Ditch E-I intercepts and carves approximately I.0 acre-feet of disturbed area runoff to Pond E. Surface runoff flows to Ditch E-2 from the 10-year, 24-hour event are calculated at 0.53 acre-feet. For the 10-year, 24-hour event, Ditch E-3 intercepts and carries approximately 0.07 acre-Feet of runoff from the stoker coal stockpile area to Pond E. Direct surface runoff inflow to Pond E from the 10-year, 24-hour event is calculated at 0.81 acre-feet. This runoff would move as overland flow from the coal stockpile and northern preparation plant azeas across the access road discharging to Pond E at a low point near the center of the pond. Material for construction of the relocated pond embankment came primarily from the existing embankment structure and both this material and any supplemental fill was free of sod, large roots, ice or frozen soil, or other deleterious materials. Fill material was placed in lifts no greater than 2 feet in thickness and compacted to 90 percent of maximum dry density. Final embankment sideslopes are no greater than 2H:IV with combined upstream and downstream slopes of SH:IV or less. Sedimentation Pond F provides sediment control for the area associated with the Shop/Maintenance Area and Access Road. Permit Renewal No. 3 Tab 1 Page 3 1/15/00