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.-~ <br />Darry Fergusson -2- January 22, 1981 <br />design storm event for spillway design. However, this does not relieve you <br />from the responsibility for submitting complete spillway design information, <br />in order to show that the ponds will in fact function properly and remain stable. <br />5. Detention time (December 18 memo) <br />Comments in this Division's review letters should not be construed as requiring <br />a 24 hour detention time. Under the interim program and also under the <br />permanent program, the operator has the option of proposing an alternate <br />detention time. However, as with spillway design, detention time must be <br />addressed in order to allow this Division to evaluate the potential for <br />achieving the effluent limitations. <br />6. Cropping factor (December 18 memo) <br />The inclusion of some sediment storage volume in pond designs is clearly re- <br />quired, and the Universal Soil Loss Equation has long been accepted as one <br />method for calculating this storage volume. However, as I explained relative <br />to peak discharge calcualtions, this Division evaluates any design for proper <br />application of the chosen estimating technique. In this instance, several <br />reasons have been presented for questioning the "C" factor you have selected. <br />I hope this explanation will help you to understand this Division's requirements <br />for an interim program sediment control design. The staff cannot recommend <br />Board approval of the Trinidad Basin amendment application until these issues <br />have been resolved. At this late date, an approval recommendation at the <br />January Board meeting will not be possible. <br />stipulated. <br />I would advise you to contact us promptly to discuss possible options for re- <br />solving these outstanding issues. As I discussed with you previously, the <br />possibility exists that some of the items in the staff review letters could be <br />I will look forward to hearing from you. <br />Sin rely, <br />~~~~ ~~~ <br />Carol Pahlke <br />Senior P,eclamation Specialist <br />CP:mab <br />cc: Vance Mills, Trinidad Basin <br />Michael McCarthy, Conover, McClearn, Heppenstall & Kearns <br />