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-17- <br /> Kock Tunnel Sediment Control <br /> Three sediment ponds in series having a total storage capacity of 11 . 1 <br /> acre-feet will be constructed to control runoff from the disturbed area <br /> at the Rock Tunnel . One pond is presently in place and the two <br /> additional ponds will be built as necessary as the size of the rock <br /> tunnel disposal area increases. All sediment accumulated over a three <br /> year period can be stored in the upper two ponds. The total runoff <br /> volume from a 10-year, 24-hour precipitation event can be stored in the <br /> lower two ponds, assuming the upper pond is full of sediment. <br /> All three ponds are equipped with 36-inch DIP emergency spillways which <br /> will pass the 257year, 24-hour peak flow. The lower two ponds are <br /> equipped with 6-inch, C4P gated dewateri•i3 pipes. The middle pond has <br /> the dewatering device located above the maximum sediment storage level . <br /> The dewatering device on the lower pond is located 2.5 feet above the <br /> bottom of the pond. The 2.5 feet of storage is for sediment in excess of <br /> three years accumulation or for sediment which is not siittled )-It in t:le <br /> upper two ponds. Even with this amount of additional dead storage, the <br /> sediment ponds are capable of containing the runoff from a 10-year, <br /> 24-hour precipitation event, as designed. <br /> Preparations Plant Sediment Control <br /> Eleven sediment ponds draining approximately 51 acres of disturbed area <br /> have been constructed at the preparations plant site. All the sedi-iient <br /> ponds are sized to contain the runoff from a 25-year, "a-hour <br /> precipitation event, plus U. 1 acre-feet of sediment per acre of disturbed <br /> drainage area. In fact, all the sediment ponds are shown by the <br /> applicant to have more storage than required. <br /> With the exception of the two lower ponds of four in series below the <br /> coal processing waste embankment and a typical cross-section on page 16 Q <br /> of Attachment 3 to Appendix II-d-7, the applicant submitted no S <br /> information on the primary and emergency spillways on preparation plant t; ? <br /> ponds. However, th,3 ponds ara sized to contain the 25-year, 24-hour <br /> storm runoff. Therefore, as long as the ponds are properly dewatered, <br /> they can safely discharge the runoff from a 25-year, 24-hour o <br /> precipitation event, as required by Rule 4.05.6(3) (d) . 10D <br /> The applicant has subsequently submitted additional information stating <br /> that principal spillways will be constructed on ponds 006, 008, 009 and <br /> 010. Ponds 007 ind 0'J9 are in series; therefore, 009 is the only, pond <br /> requiring a principal spillway. Pond 011 discharges into the ditch <br /> leading to the four ponds at discharge point 001 . All the above ponds <br /> will be dewatered within 24 hours following any runoff event to maintain <br /> adequate storage. <br /> Coal Processing ',taste E,nhankment Sediment Control <br /> A system of two sediment ponds is planned to 'be constructea for the <br /> two-year coal processing 4aste disposal area. These ponas will treat the <br /> drainage from an area of 5.55 acres. The two ponds are designed to •lave <br />