2011-09-09_APPLICATION CORRESPONDENCE - C2010089 (2)

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C- 2010 -089 PAR No. 2 New Horizon North Mine 9- Sep -2011 Page 17 of 25 b) In Table 2 on page 4 of the Arcadis report in Appendix 2.05.3(4) -1, a primary discharge pipe length of 247 feet is given for sediment pond NHN -002. However, referring to Figure 3 of the same report, the pipe length appears to be about 60 feet. Please clarify. 14. Response accepted. 15. Response accepted. 16. Response accepted. 17. The Sedcad designs contain two runs for the "Collection Ditch Design for Pond NHN -002 South ". The first design run appears to have used parameters from the previous run for "Collection Ditch Design for Pond NHN -002 North ". Please eliminate the incorrect Sedcad design run for NHN -002 South. DRMS: The Division has no further concerns with this question. The first design run was removed in the May 26, 2011 submittal. However, the Division has additional questions concerning culverts and ditches. a) The Sedcad hydrology design for Channel -1 consists of one ditch design page that is located at the back of Appendix 2.05.3(3) -1, "Sedcad Runs for Culverts ". Please include additional design pages that show how the peak discharge for Channel -1 was obtained, as was done for the other ditches. Also, in order to avoid any confusion, please consider moving the channel -1 Sedcad run pages to a more appropriate section, such as Appendix 2.05.3(4) -2, "Sedcad Runs for Pond and Diversions ". Also, please consider adding Channel -1 to Table 4: Ditch Design Parameters on page 7 of Appendix 2.05.3(4) -1, "Arcadis Report on Sediment Control ". b) In Appendix 2.05.3(3) -1, "Sedcad Runs for Culverts ", there are Sedcad design sheets for culvert C -1 that use a peak discharge of 4.78 cfs and a culvert diameter of 18 inches. These parameters also appear in the Culvert Table on Map 2.05.3(3) -1 for that culvert. However, directly after those design pages is one design page for culvert C -1 that uses a peak discharge of 51.82 cfs. Please explain. c) The Culvert Table on Map 2.05.3(3) -1 states that the subwatersheds for culvert C -13 are SW1 -B and SW -FA. However, referring to Map 2.05.3(3) -1, it appears that the subwatersheds should be SW -1C and SW -FA. If this is correct, please revise the Sedcad designs and the Culvert Table on Map 2.05.3(3) -1 for culvert C -13. d) Please add the D50 riprap size of.6 inches for ditch NHN -002 South w /Riprap to Table 4: Ditch Design Parameters on page 7 of Appendix 2.05.3(4) -1, "Arcadis Report on Sediment Control ". 18. Response accepted. 19. As was done for the curve number of 91 on the second page of the Pond Design Memo in Appendix 2.05.3(3) -1, please justify the use of the curve number of 79 for the subwatersheds for culverts C -6 and C -6A. DRMS: In the May 26, 2011 submittal cover letter, Western Fuels explained the justification for using the curve number but did not revise any text since the culvert was not in the mine's disturbed area. The Division's question could have been worded better. The justification for the curve number of 91, used in the Sedcad design runs for all mine disturbed area ponds, ditches and culverts, appears on page 2 of Appendix 2.05.3(4) -1.