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1 • • <br />B. 12/20/79 Memorandum from J. Zimpfer and T. Gibson to Rick <br />Mills <br />12/20/79 Memo, p. 1, #1 <br />Sediment Control System- <br />Ponds- <br />"1. Several of the assumptions used to estimate sedi- <br />ment storage (the CP factor, sediment density, and the <br />sediment delivery ratio) may somewhat underestimate <br />sediment storage volumes. None of the assumptions so <br />severely underestimates storage that redesign is required, <br />but this is some concern on our part. The applicant <br />should commit to a yearly cleanout of all ponds, even <br />when not 608 full." <br />See, page 816-45(a)-(d) <br />12/20/79 Memo, p. 1, #2 <br />"2. The detention time calculations have not been <br />submitted for ponds having a type-three riser. Select <br />any one pond as an example, and submit a calculated <br />dewatering time for the 10 year, 24 hour runoff." <br />Page 13 of Exhibit 13 states that a flood routing <br />for pond K was done. Flood routings for ponds C <br />and K, both of which have type-three risers, were <br />included in the backup calculations found in <br />Volume 11, 1/11/80 Supplement to Exhibit 13, <br />Appendix B, Pond Hydraulics Section. The calcula- <br />tion sheets show the centroids of the outflow <br />hydrographs at 42 and 37 hours, respectively. <br />This indicates theoretical detention times of 41~ <br />and 36 hours respectively. <br />See, also p. 816-46(a) and (b) <br />12/20/79 Memo, p. 1, #3 <br />"3. The inflow and outflow to ponds F and G (see map <br />13) appear to be located so close together that the <br />ponds might be susceptible to short circuiting. Ponds <br />should be redesigned or submit calculations to demon- <br />strate that short circuiting is not a problem." <br />