2012-12-17_REVISION - C2010089 (2)

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Doug White, Western Fuels C -2010 -0891 MR -02 & TR -01 PAR Dec. 17, 2012 Page 2 of 4 assuming the gates are fully open to determine whether runoff from the design event will meet the effluent standard in the event that the gates are open when a major storm occurs (Rule 4.05.6(3)(a)), and another assuming the gates are fully closed to ensure that the primary spillway is sized to treat and convey the design runoff without discharge through the emergency spillway (Rule 4.05.9(2)(b)) in the event that the gates are in the closed position when a major storm occurs. The rationale for this modeling methodology is also explained in Appendix 2.05.3(4) -1 of the New Horizon North permit application package, beginning on page 4. 2. The as -built designs for pond NHN -001 include a revised Eroded Particle Size Distribution (EPSD), labeled "New Horizon Mine 1 ". This EPSD differs from the previously approved EPSD for NHN -001, and is also dissimilar to any of the EPSDs in the approved New Horizon Mine 1 and 2 designs also labeled "New Horizon Mine 1 "). Please explain the basis for this distribution. If this particle distribution is based on site soil samples, please provide a copy of the laboratory report used for the distribution. 3. Page 5 of section 2.05.3(4) of the approved permit application package notes that mine water, at a rate of 1 -2 cfm, may be pumped from the pit to Pond 001, 002, or 003. This pit water inflow does not appear to be accounted for in the SEDCAD design, as required by Rule 4.05.6(3)(a). Please either revise the SEDCAD design to include this base flow /permanent pool (Rule 4.05.9(2)), or state that pit pumping will only occur when the sediment pond is at or below the weep hole elevation and that the pond will be dewatered within 24 hours. It should be clear that in no case will pit water pumped into the pond result in the passage of runoff from the 10 -year 24 -hour event through the emergency spillway (Rule 4.05.9(2)(b)). 4. The placement of the primary spillway in the as -built configuration of pond NHN -001 differs from the design. The spillway has been placed west of the approved location, closer to the inlet of Ditch NHN -001 West. This location may result in short- circuiting of the pond. Please indicate, in accordance with Rule 4.05.6(6), how WFC will ensure that the pond is not short - circuited with Ditch NHN -001 West inflows. 5. Please include design information for the emergency spillway channel to indicate the flow depth and demonstrate adequate embankment height to ensure 1' of freeboard, as required by Rule 4.05.9(7)(d). 6. The SEDCAD run provided for pond NHN -001 is based on one 114.9 acre watershed. The run also includes Muskingum routing information. The SEDCAD User's Manual indicates that this routing function is used when there are multiple subwatersheds and a given subwatershed does not flow directly to the design structure but rather is routed (via ditch, culvert, etc.) to the structure. This does not appear to be the case with the NHN - 001 watershed. Please revise the design to omit this routing or break the watershed into the subwatersheds indicated on Map 2.05.3(4) -1 and include appropriate routing for each subwatershed and structure.