2017-05-12_PERMIT FILE - C2010089A (4)

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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 area. Sedimentation ponds or impoundments will be constructed before creating new disturbances, unless approved drainage diversions or other surface water control structures are installed. Appendix 2.05.3(4)-1 contains the design of the sediment control facilities for NHN. Subsequent designs and as -built certifications for ponds NHN-001 and NHN-002 and their collection ditches supersede the designs included in the Appendix 2.05.3 (4)-1 for the same structures. The as -built certification for Pond NHN-001 is located in Appendix 2.05.3(4)-6 and the as -built certification of the Pond NHN-001 collection ditches is located in Appendix 2.05.3(4)-7. Also, a new design for Pond NHN-002 and its collection ditches is located in Appendix 2.05.3(4)-8. Finally, the as - built certification for Pond NHN-002 is located in in Appendix 2.05.3(4)-10. Collection Ditch and Culvert Design Parameters The main collection ditches in the permit area are the NHN-001 East and West, The NHN-002 North and South, and the NHN-003 North and South Ditches. These ditches are used to transport runoff into Sedimentation Ponds NHN-001, NHN-002 and NHN-003 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)-1. Culvert designs are presented in Appendix 2.05.3(3)-1 and were designed using SEDCAD software. Subwatershed 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. Culvert C-7 was designed using a curve number of 81 since the watersheds consist of a herbaceous mixture of grass, weeds, and low - growing brush (Arid and Semiarid Rangelands) with fair hydrologic conditions (30%-70% ground cover) in hydrologic soil group C and are not a part of the mine disturbance area. All ditches were designed in accordance with applicable regulations in 4.05.3. Designs for all Ditches in the Permit Area Steps taken in the ditch designs are outlined in Appendix 2.05.3(4)-1, Appendix 2.05.3(4)-2B, and Appendix 2.05.3(4)-8. Designs presented in Appendix 2.05.3(4)-8 for NHN-002 North and South Ditches supersede designs presented in Appendix 2.05.3(4)-1. Sedimentation Ponds Sediment pond design details are discussed in Appendix 2.05.3(4)-1 as well as Appendix 2.05.3(4)-8 for Pond NHN-002. Designs presented in Appendix 2.05.3(4)-8 supersede all Pond Section 2.05.3(4) Page 2 April 2016 (PR -01)