2014-11-04_PERMIT FILE - C2010089A

Home Browse Search

Introduction Pond NHN -002 at the New Horizon North Mine is designed to capture and contain the runoff from the 10 -YR, 24 -HR storm event as part of sediment control at the mine. This appendix contains design specifications for Pond NHN -002 and its feeding ditches, NHN -002 North and NHN -002 South. Included in these designs are the stormwater runoff values for the 10 -YR, 24- HR event that the ditches and pond must contain and control, and the 25 -YR, 24 -HR event that the pond must pass safely through its emergency spillway. Stormwater Data Pond NHN -002 is the sediment pond for the stormwater drainage watershed SW2 shown on Map 2.05.3(4) -1. Runoff from this area flows entirely to the ditches that feed Pond NHN -002 or the pond itself. Map 2.05.3(4) -9 shows the breakdown of SW2 into subwatersheds that each feed a separate part of the Pond NHN -002 stormwater control system. SW2 -A feeds NHN -002 South, SW2 -13 feeds the pond directly, and SW2 -C feeds NHN -002 North. Table 2.05.3(4) -8 -1 shows a summary of the runoff values for each subwatershed. This data can also be seen in SEDCAD models located in this Appendix. In addition to the subwatersheds, Pond NHN -002 also will handle pit pumping, which can be seen in the Table 2.05.3(4) -8 -1. The10 -YR runoff and peak flows are from SEDCAD Model 1 (As shown later in this Appendix); the 25 -YR peak flow is from SEDCAD Model 2 (As shown later in this Appendix). Table 2.05.3(4) -8 -1 Subwatershed Area 10 -YR, 24 -HR 25 -YR, 24 -HR acres Runoff (ac -ft) Peak Runoff Peak Flow (cfs) (ac -ft) Flow (cfs) SW2 -A 23.33 2.24 23.96 SW2 -B 34.49 3.36 38.43 SW2 -C 29.54 2.76 27.93 SW2 Combined 1 89.06 18.59 190.93 113.40 Pit Pumping* N/A 0.164 2.01 *Pit pumping is the same regardless of storm size. APPENDIX 2.05.3(4) -8 PAGE - 3 - September 2014 (TR 06)