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mining areas. The location of each ditch can be found on Exhibits 13-2 and 13-2A. The design <br />• information can be found in Attachment 13.2. <br />Each ditch has been designed and will be constructed in accordance with the applicable regulations in <br />4.05.3. Diversions will be designed, constructed, and maintained in a manner which prevents <br />additional contributions of suspended solids to streamflow and to runoff outside the permit area, to the <br />extent possible, using the best technology currently available. Appropriate sediment control measures <br />for these diversions may include, but not be limited to, maintenance of appropriate gradients, channel <br />lining, revegetation, roughness structures, and detention basins. No diversion will be located so as to <br />increase the potential for landslides. When no longer needed, each temporary diversion will be removed <br />and the affected land regraded, topsoiled, and revegetated in accordance with 4.06, 4.14, and 4.15. If <br />the temporary diversion was for an ephemeral stream, the channel will be reestablished to functionally <br />blend with the undisturbed drainage above and below the area to be reclaimed. Diversion design will <br />incorporate the following: <br />lal Channel linings, including channel riprap, will be designed using standard engineering <br />practices to pass safety the design velocities. <br />Ibl Freeboard will be no less than 0.5 feet. Protection will be provided for transition of flows <br />and for critical areas such as swales and curves when excessive velocities are anticipated. <br />Icl Energy dissipators will be installed when necessary at discharge points, where diversions <br />intersect with natural streams and exit velocity of the diversion flow is greater than that of <br />the receiving stream. <br />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 approved NPDES permit, SCC will primarily use sedimentation ponds <br />to prevent, to the extent possible, additional contributions of sediment to streamflow or runoff outside <br />the permit area due to mining disturbance Isee Exhibits 13-2 and 13-2A1. Please refer to Attachments <br />13-3, 13-4, and 13-5 for pond designs. <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 10- <br />year, 24-hour precipitation event and to meet all applicable State and Federal regulations for <br />all effluent limitations before discharge from the permit area. The characteristics of the <br />mine site, reclamation procedures, and onsite sediment control practices are also considered <br />. in the design. <br />3 Revised 9/98 <br />