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C/F,?o Oo7 <br />Ito <br />CAe <br />Pond Design Checklist <br />Pond: Mine water settling pond next to 017 <br />Mine: West Elk Date of this review: .SJ?¢?d y <br />Permit No.: C-80-007 CDRMS reviewer: Tom Kaldenbach <br />Revision: TR-116 <br />1. Can the pond contain or treat runoff from 10-yr, 24 hr + mine inflow + spring inflows <br />(4.05.6(2)(a)? <br />Yes. Submittal notes 10-year event will cause minimal inflow and rise in water <br />level. <br />2. Will spillway safely pass, with 1-ft. freeboard, a 25-yr., 24-hr. event + mine inflow + spring <br />inflows? <br />No spillway is planned or required because, as allowed under 4.05.9(2)(e), storage <br />is primarily being relied on for controlling runoff from the 25-year storm event. <br />3. Is sediment storage volume adequate so that clean-out is not necessary more frequently than <br />once every, say, 3 years? <br />Yes. If mine inflow contains 100 mg/1 of sediment (a high historical value for outfall 017), <br />and there is the pond has the designed 400 gpm continous flow-through, and half of this <br />sediment accumulates in the new pond, the accumulation rate would be 1538 mg/minute. At <br />2700 pounds per cubic yard, this accumulation rate will amount to 1.8 cubic yards per day, <br />which would fill the pond to the 1.7 acre-foot clean-out level in 4.2 years. <br />4. For combination principal/emergency spillway, is emergency spillway crest at least 1 ft. <br />above crest of principal spillway (Section 4.05.6(4))? <br />No spillway, see 2, above. <br />5. Is open channel constructed of materials that will not erode at predicted peak discharges? <br />No spillway, see 2, above. <br />6. Are combined embankment side slopes steeper (less) than 5:1?