2012-01-13_APPLICATION CORRESPONDENCE - C2010089 (2)

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C -2010 -089 New Horizon North Mine PARNos. 1- to -1B, 2- 2A -2B, 3 Page 38 of 60 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- I to Table 4: Ditch Design Parameters on page 7 of Appendix 2.05.3(4) -1, "Arcadis Report on Sediment Control ". <�e(lc t cl i-e ,vitTiis ii,(�i -e tichicle d in A1)1)enc1h 2.0 .3( ). Item resoh,ed qtr Dec-2011 response. 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, Ilre c °nl .,r.t t �1 cdes rrl>crl;e rr> ir � .� ? cis wus cdeleted' Item resolved in Dec-2011 response; c) The Culvert Table on Map 2.05:3(3) -1 states that the subwatersheds for culvert C -13 are SWl -B and SW -FA. However, referring to Map 2.053(3) -1, it appears that the subwatersheds should be SW -IC 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. AIalr 2 05n 30 was r °enarrnT�ir °ec1 ctsll�crl��',il �a,� -� } ®1 c��pcd r °ei,�c�c1 �d�e .�c�cdc�cr��e�i� t� °cr.� crlA�c� rc3rz.�ecl Item reaso vet in Dec-20-11 rest -)tense, 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 ". The tart in the Ar°cadis rel)ort �rcis i- evisect Item resolved in Dec- 2011 response. 18, On Map 2.05,3(3) -1, Surface Water Hydrology, the acreage for subwatershed SW -MD is shown as being 103,02 acres. This watershed is appropriate for the design of culvert C -6 but the design of culvert C -6A should also take into account the subwatershed of Meehan Draw and the undisturbed wetland. Please revise the Sedcad design for culvert C -6A accordingly. Itent resoh,ed in cty- 2011 r eslronse 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. 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. However, there do not appear to be stated justifications for the use of curve number of 79 for culverts C -6A and C -613 and the use of a curve number of 89 for culvert C -12. The Division requests that the appropriate section of the permit application be updated to detail the justifications for using