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• -12- • ~s generated by this method based on values generated by other methods, informs oration on this method is contained in Section III of Appendix Q~ The operator used an estimate of 2.0 inches of precipitation for a 25~year, 24-hour storm for design purposes. Diversion and Collection Ditches The majority of existing and proposed ditches at the Trapper Mine site divert the runoff from active pits into downstream sediment ponds, Utah International, Inc. has produced estimates of the peak flows to be expected from the 2-year, 24-hour storm and has adequately designed the ditches to convey these flows. Several sections of ditch had slopes which exceeded lo, increasing the possibility of erosion. In discussions with the Division and based on addi- tional information incorporated into the permit, it was demonstrated that these areas would not experience erosion as designed. Sediment Ponds There are presently 16 structures designed as sediment control ponds on the site. The applicant is also using an abandoned pit, the Empire Energy Pit, for sedi- ment control. This pit does not meet aII of the specific design requirements of 4.05.6. For the following reasons, the Division deems it unreasonable to impose the specific design requirements of 4,05.6: (]) The pit is an existing disturbance and will be reclaimed by Utah International after it is no longer needed for sediment control. (2) It is capable of storing well over the 10-year, 24-hour storm volume without discharge, and has more than adequate sediment storage volume. (3) Failure is extremely unlikely under any event. All ponds have been found to be adequately sized for both sediment storage and flood volume resulting from the 10-year, 24-hour storm. All ponds have been professionally certified. For all ponds storing more than two acre-feet of water without any means of discharge, the acquisition of water storage rights is required. Four ponds at the Trapper Mine exceed 2 acre-feet of dead storage. The applicant has applied for water storage rights and evaporation losses for dead pool storage in District 6 [9a ter Court. There are eight sediment ponds proposed to be constructed durin_q this ,permit term by the applicant, for which no design information has been given. The applicant has committed to the submission of design information to the Division and obtaining approval prior to construction. The applicant has committed to satisfying the requirements of Rule 9,05,6(9) and obtaining written approval of the Division prior to removal of any sedi- n~ntation ponds.