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• Note: <br />- Column (2) is calculated based on the revised USLE and a 60% sediment <br />delivery ratio <br />- Column (3) = Column (2 x 2000 lb/ton <br />80 lb ft3 x 356 <br />- Column (4) = Column (3) x 3 years <br />- Column (5) = Column (4) x 40% <br />- Column (6) is from Appendix 7-11A <br />- Column (7) = Column (6) - Column (5) <br />- Column (8) = Column (7)/Column (3) (Estimated life before sediment <br />cleanout would be required) <br />Based on the above, Peabody has estimated the volume of sediment storage <br />that would exist when pond maintenance would be required to restore the <br />sediment storage capacity (i.e., 40 percent of the estimated revised USLE <br />3-year sediment generation, Column (5)). Also see applicable attached <br />graphs. This assumes 60 percent of the 3-year sediment storage volume is <br />• filled with sediment and 40 percent or 1.2 years (i.e., 40 percent of 3 <br />years) of sediment storage remains in the pond. <br />Based on the above and the information contained in Technical Revision <br />#15, a less frequent than annual sediment survey would be permissible and <br />still provide Peabody and CMLRD ample warning (i.e., 40 percent of 3-year <br />sediment storage or 1.2 years prior to the required pond maintenance) <br />while still allowing adequate detention time for the 10-year, 24-hour <br />precipitation event. The maintenance requirements for these ponds will <br />also reduce as mining operations are completed and more of the watersheds <br />are reclaimed. This will reduce the predicted USLE sediment yield. <br />C~ <br />