2016-01-07_PERMIT FILE - C2010089A

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5) Linear detention and filtering structures that include filter fence, straw bale barrier, brush barrier, and filter berms; 6) Measures used in conjunction with overland conveyances including check dams, sediment traps, and water level spreaders; 7) Vegetative filters, temporary cover crops, reestablished permanent vegetation covers, etc. 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. WFC retained Arcadis U.S., Inc. to assist in the design of sediment and water control facilities such as sediment ponds and ditches. A copy of the Arcadis report is attached with this section as Appendix 2.05.3(4)-1. The Arcadis report is only applicable to Pond NHN-003 as of Technical Revision 05. An as -built of Pond NI -IN -00 1 can be found in Appendix 2.05.3(4)-6, and specific designs for Pond NHN-002 can be found in Appendix 2.05.3(4)-8. The specific designs for Pond NHN-002 structures replace any Arcadis designs for the same pond and ditches. Collection Ditches, Culverts and Diversion 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 N14N-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 Figure 1 of the Arcadis report. Pond NHN-002 drainage areas are delineated on Map 2.05.3(4)-9. Culvert designs are presented in Appendix 2.05.3(4)-2. Culverts were designed using SedCAD software. Subwatershed areas were created for each of the areas flowing to the individual culverts. In general a curve number of 91 was used in the SedCAD program for all of the areas that were disturbed. Three culverts were designed using different curve numbers. Two of the culverts, C -6A and C-613 were designed using a curve number of 79. This use was justified as the watersheds SW -MD and SW-MD2 consist of pasture or rangeland with fair hydrologic conditions and hydrologic soil group C as shown in the SedCAD software and are not a part of the mine disturbance area. The third culvert, C-12, was assigned a curve number of 89 which is compatible with its watershed area, SW2-D, which is a gravel road. All ditches were designed in accordance with the applicable regulations in 4.05.3. Diversions will be designed, constructed, and maintained in a manner which prevents additional contributions of suspended solids to stream flow and to runoff outside the permit area, to the extent possible, using the best technology currently available. Appropriate sediment control measures for these diversions may include, but not be limited to, maintenance of appropriate gradients, channel lining, revegetation, roughness structures, and detention basins. No diversion Section 2.05.3(4) Page 2 Sept. 2015 (TR -11)