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A number of concerns were noted by the Division during the review regarding <br />sizing calculations, design details, and sediment clean out for proposed <br />structures. The Division also noted that design velocities in a number of the <br />ditches may be erosive. Revised designs and information submitted by the <br />applicant and incorporated into the application have adequately addressed <br />these concerns. <br />The proposed pond embankment will have a vertical height of 12 feet (10 feet <br />to the bottom of the emergency spillway). The pond will have a capacity of <br />4.32 acre feet which will allow for sediment storage and runoff and mine water <br />containment. The pond will be equipped with a dewatering siphon at the 100% <br />sediment storage level, a principal spillway designed for the 25-year, 24-hour <br />event and an emergency spillway designed to pass safely the 100 year-24 hour <br />event. To aid in the settling of fine textured suspended solids picked up <br />within the mine, Dowell M-178 Flocculent (a cationic flocculent) will be <br />injected into the water line. Sediment dredged from the pond is disposed of <br />within the underground development waste disposal site. Clean out will be <br />initiated when the sediment level reaches 60% of the design sediment capacity. <br />The applicant has committed to riprap ditches 8, 9, 11 and 12, which were <br />noted by the Division as having potentially erosive velocities. <br />The application requests an exemption from the sediment pond requirement of <br />Rule 4.05 for a 1 acre area in the vicinity of the mine fan, a .4 acre area <br />which includes the bathhouse and employee parking lot and a .48 acre area at <br />the powder magazine. Alternative sediment control measures (gravel surfacing <br />and berms) will be employed to provide adequate sediment control for these <br />small areas. <br />Pursuant to Rule 4.05.2(3) the Division is granting an exemption for the above <br />areas based on the following findings: <br />(a) Based on the small size and light use of the areas and the <br />alternative sediment control measures to 6e employed, a <br />sedimentation pond will not be required for the drainage to meet the <br />effluent limitations of Rule 4.05.2 and applicable State and Federal <br />requirements. Berms will be maintained around the perimeter of each <br />exempted area. The berms, in combination with gravel surfacing will <br />insure that water from the design event is contained and infiltrates <br />rapidly. <br />tb) The disturbed surface area within the total disturbed area is small <br />(approximately 1.9 acres) and the drainage will not be mixed with a <br />discharge from underground mine workings. <br />A small area (less than 1/2 acre) at the belt portal and intake portal for the <br />Red Canyon No. 1 Mine currently drains into the mine where it mixes with mine <br />water in an underground sump and is pumped into the sedimentation pond prior <br />to discharge. Similarly, the runoff from the surface of the proposed Mine No. <br />2 portals and yard area (2.5 acres) will drain into the portals, mix with mine <br />water and be pumped into the sedimentation pond. Given the small drainage <br />areas involved and the fact that surface water would mix with mine water in <br />the sedimentation pond even if it was diverted away from the portals, the <br />drainage plan is approved by the Division. <br />-15- <br />