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Sediment and Runoff Control <br />Details of the sediment control plan for the operation are provided in <br />Section 2.05,3(4) of the permit application. The components of the plan <br />consist of a sedimentation pond, temporary diversion ditches and sediment <br />collection ditches. The temporary diversion ditches will be used to conduct <br />flow from the undisturbed area around the disturbed area. The sediment <br />collection ditches will be used to route flow from the disturbed area into the <br />sedimentation pond. <br />The sediment pond has been approved under a design standard which was required <br />by the Division, This plan was required to mitigate the effects of the <br />existing disturbance in the area. The approved pond provides; 1) adequate <br />capacity for the storage of runoff from the 10-year, 24-hour event <br />(.089 acre feet); 2) sufficient capacity for a three-year accumulation of <br />sediment (0,3 acre feet); 3) an automatic dewatering device which will dewater <br />the pond within 72 hours of a storm event while providing a theoretical <br />detention time of 24 hours; and 4) a spillway configuration which will be <br />stable under the required conditions, <br />It is stated in the application that the sediment pond will be cleaned when it <br />reaches 60% of sediment storage capacity. However, no provisions have been <br />made for monitoring sediment storage to determine when the 60% level will be <br />attained. For this reason, the Division requires the following stipulation: <br />Stipulation No: 1: <br />WITHIN 30 DAYS OF PERMIT ISSUANCE, THE PERMITTEE WILL SUBMIT A STATEMENT <br />CERTIFIED BY A REGISTERED PROFESSIONAL ENGINEER ATTESTING THAT THE <br />SEDIMENT POND HAS BEEN CONSTRUCTED AS DESIGNED. THE STATEMENT WILL ALSO <br />DESCRIBE HOW THE SEDIMENT STORAGE MONITORING IS GOING TO BE IMPLEMENTED. <br />Rimrock Coal Company has also committed to submitting a quarterly inspection <br />report for the sedimentation pond to comply with Rule 4.05.9(11 )(c ). <br />Sediment collection ditches will be constructed to conduct flow from the <br />disturbed area into the sedimentation pond. The applicant has designed these <br />ditches for the 10-year, 24-hour storm event. <br />Temporary diversion ditches will be installed above the disturbed area to <br />collect undisturbed flows, route them around the disturbed area and discharge <br />below the disturbance. The applicant has demonstrated that all ditches will <br />be stable under flow conditions produced by the theoretical 10-year, 24-hour <br />event. <br />-9- <br />