2018-07-02_PERMIT FILE - C2010089A

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4. Linear detention and filtering structures that include filter fence, straw bale barrier, brush barrier, and filter berms; 5. Measures used in conjunction with overland conveyances including check dams, sediment traps, straw wattles, and water level spreaders; All surface mining operations will be conducted to achieve the effluent limitations of 4.05.2(7) for all mixed drainage when it leaves the permit. Sedimentation ponds or impoundments will be constructed before creating new disturbances, unless approved drainage diversions or other surface water control structures are installed. The as -built for Pond NHN-001 is located in Appendix 2.05.3(4)-6 and the as -built for the Pond NHN-001 collection ditches is located in Appendix 2.05.3(4)-7. A new design for Pond NHN-002 and its collection ditches is located in Appendix 2.05.3(4)$ and the as -built for Pond NHN-002 is located in in Appendix 2.05.3(4)-10. Finally, the design for the NHN-001 East Ditch Extension is located in Appendix 2.05.3(4)-11. Culverts Design Parameters Culvert designs utilizing SEDCAD software are provided in Appendix 2.05.3(3)-l. Sub - watershed areas were created for each of the areas flowing to the individual culverts. For disturbed areas, a curve number of 86 was used in SEDCAD for bare soils in hydrologic soil group B. All ditches were designed in accordance with applicable regulations in 4.05.3. Ditch Designs The main collection ditches in the permit area are the NHN-001 East and West Ditches and the NHN-002 South Ditch. These ditches are used to transport runoff into Sedimentation Ponds NHN-001 and NHN-002 for treatment in accordance with the requirements of applicable regulations. The location and drainage area of these ditches can be found on Map 2.05.3(4)-l. Ditch designs are presented in several different appendices and are further outlined below by the appropriate stationing on the ditches. Sedimentation Ponds In accordance with Rule 4.05.2, NHN will use Ponds NHN-001 and NHN-002 to prevent, to the extent possible, additional contributions of sediment to stream flow or runoff outside the permit area due to mining disturbance. In accordance with Rule 4.05.6(3) each sedimentation pond is designed, constructed, and maintained to: a. Provide storage for runoff or inflow into the pond as a result of a 10 -year, 24-hour precipitation event and to meet all applicable State and Federal regulations for effluent limitations before discharge from the permit. The characteristics of the mine site, reclamation procedures, and sediment control practices are also considered in the design. b. Provide adequate sediment storage volume in compliance with the DRMS regulations. c. Install an appropriate non -clogging dewatering device to maintain a 10 -year, 24-hour storage volume. Section 2.05.3(4) Page 2 March 2018 (TR -16)