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Idl Excess excavated material not necessary for diversion channel geometry or regrading of the <br />channel will be disposed of in accordance with 4.09. <br />lel Topsoil will be handled in compliance with 4.06. <br />Sedimentation Ponds <br />In accordance with 4.05.2 and the NPDES permit, SCC will primarily use sedimentation ponds to <br />prevent, to the extent possible, additional contributions of sediment to streamflow or runoff outside <br />the permit area due to mining disturbance (see Exhibit 13-2, Surface Water Control Plan, and Exhibit <br />13-12.1, Yoast Watershedl. Please refer to Attachments 13-3, Design Report Sediment Structure <br />Pond 010; 13-4, Design Report Sediment Structure Pond 011; and, 13.12, Drainage and Sediment <br />Control Plan, far pond designs of 012, 013 and 014. <br />The sedimentation ponds and impoundments are designed, constructed, and maintained to achieve the <br />following: <br />a. Provide storage and treatment for the runoff or inflow entering the pond as a result of a <br />10-year, 24-hour precipitation event and to meet all applicable State and Federal <br />regulations for all effluent limitations before discharge from the permit area. The <br />• <br />characteristics of the mine site, reclamation procedures, and onsite sediment control _ <br />practices are also considered in the design. • <br />b. All sedimentation ponds are designed to provide adequate sediment storage volume in <br />compliance with the CDMG regulations. <br />c. An appropriate nonclogging dewatering device will be installed to dewater a 10-year, 24- <br />hour storage volume. <br />d. Appropriate combinations of principal and emergency spillways to safely discharge the <br />runoff from a 25-year, 24-hour precipitation or larger event, as required by the CDMG <br />regulations, will be installed in all ponds. <br />The sediment storage capacity of each sedimentation pond or impoundment will be monitored on an <br />annual basis to ensure that at least one year of sediment storage is available beneath the principal <br />spillway inlet (based on R.U.S.L.E.1. When adequate capacity is no longer available, sediment removal <br />or other corrective actions will be taken to restore adequate sediment storage capacity to the pond. <br />SCC will monitor the sediment storage capacity of each pond with one or a combination of the <br />following methods, as applicable: <br /> <br />4 Revised 2/99 <br />