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-17- <br /> }lock Tunnel Sediment Control <br /> Three sediment ponds in series having a total storage capacity of 11 . 1 <br /> acre-feet gill 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 CMP emergency spillways 'which <br /> will pass the 257year, 24-hour peak flow. The lower two ponds are <br /> equipped with 6-inch, CMP gated dev4ateri,rg 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 fiet 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 s,ittle,J oat in t:ne <br /> upper two ponds. Even with this amount of additional dead storage, the <br /> sediment ponds are capable of containing the runoff fro"n a 10-year, <br /> 24-hour precipitation event, as designed. <br /> Preparations Plant Sediment Control <br /> Eleven sediment ponds draining approximately 51 acres of dist"arhed area <br /> have been constructed at the preparations plant site. All the Sedi.nent <br /> ponds are sized to contain the runoff from a 25-year, 2a-hour <br /> precipitation event, plus 0. 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-3-7, the applicant submitted no <br /> information on the primary and emergency spillways on preparation plant tt <br /> ponds. However, the po"r.is ara sized to contain the 25-year, 1-4-hour S r� <br /> storm runoff. Therefore, as long as the ponds are properly dewatered, (tS <br /> they can safely discharge the runoff from a 25-year, 24-hour <br /> precipitation event, as required by Rule 4.05.6(3) (d) . <br /> The applic:ant has subsequently submitted additional inf)wnation stating <br /> that principal spillways will be constructed on ponds 006, 008, 009 and <br /> 010. Ponds 307 and 'Y)9 are in series; therefore, 009 is the only pond <br /> requiring a principal spillway. Pond Oil discharges into the ditcn <br /> leading to the four ponds at discharge point 001 . All tle above ponds <br /> will be dewaterea within 24 hours Following any runoff event to maintain <br /> adequate storage. <br /> Coal Processing 'Haste E,nhankmeznt Sediment Control <br /> A system ;F t.vo sediment ponds is plannea ,.o ''r)e constr-ictea for the <br /> t,vo-fear cca 1 processi ng vaste di sposa, area. T'iPs,� ;:anas 'Ni I l treat the <br /> :rainaye rr,.m an area of 5.55 acres. Th: two ponds ar' ;es i,�ned <br />