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RESPONSE: • C The proposed Sedimentation Pond n007's design has been revised and resubmitted to CL.-1R6. a. In the revised design, SEDIMOT II Computer model was used to predict sediment storage based on M.U.S.L.E. calculations. This question is no longer relevant. b. The emergency spillway was revised to include a riprapped channel and a Manning's "n" value of 0.04 was used in the design. This question is no longer relevant. c. This question is addressed in the revised design. A 6" drop inlet principal spillway was designed which allows for adequate storage of the 10-year, 24-hour storm volume and also allows for 1 ac-ft of pit pumpage without any discharge through the emergency spillway. An outflow hydrograph is provided in the revised design which indicates adequate detention time in order to treat the 10-year, 24-hour storm volume in accordance with regulations 4.05.6 and 4.05.2. 2.05.3(4) Ponds, Impoundments ar,d Diversions 5. Sediment volume requirements for Pond 007 are based on weighted-average K values and a CP value of I. The Division considers these estimates to be accurate. The methodology used • in the design of Ponds 002, 003, and 004, however, use C values less than 1.0 and K values are assigned without reference to soil type or an area-weighting procedure. Because the application states that annual sediment volwne surveys will be provided at these ponds, no recalculation of annual sediment delivery for pond design purposes is necessary in the application. RESPONSE: The designs of Sedimentation Pond n002, 003, and 004 have been revised using SEDIMOT II. A weighed "K" factor was calculated for each pond and the sediment storage volume was recalculated for each pond. All of the sedimentation ponds will be designed and constructed to contain a minimum of two years of 'sediment storage based on the U.S.L.E. calculations or more than one equivalent design storm's sediment inflow based on the M.U.S.L.E. calculations. 'rJhen the pond's sediment storage volume becomes less than or equal to one year of sediment storage based on the U.S.L.E. calculations, or less than a minimum of one equivalent design storrti's sediment inflow based on the M.U.S.L.E. calculation, Peabody Coal Company will restore the above minimum sediment storage volume. The sediment storage volume will be determined based on annual field surveys of the pond's storage volume; aerial surveys, and volume • calculations of the pond's storage capacity; measuring the difference 8 Revised 8/27/86