2013-02-20_REVISION - C2010089 - Laserfiche WebLink

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Page 2 of 6 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. WFC: The EPSD in the four SEDCAD runs included with this application has been revised to match the previously approved EPSD for Pond NHN-001. DRMS: Response accepted. 3. DRMS: 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)). WFC: All four SEDCAD run cases included with this submittal were run using a designed null structure #1 with watershed information set to simulate approximately 2 cfs (1.96 cfs) of pit water pumping, with the initial pool elevation at 5671.5 ft., the gated valve elevation. SEDCAD calculated no discharge through the emergency spillway for all four cases. DRMS: Response accepted. 4. DRMS: 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. WFC: The approved Pond NHN-001 principle spillway was located approximately 290 feet from the inlet of Ditch NHN-001 West. The as-built principle spillway was relocated to accommodate alignment with the existing county road culvert, and is approximately 215 feet from the inlet of Ditch NHN- 001 West. This distance is closer than the approved design of Pond NHN-001, but exceeds the distance approved by DRMS in the design for Pond NHN-002, which shows the inlet of Ditch NHN-002 North located approximately 160 feet from the principle spillway, still a sufficient distance to prevent short circuiting. This assertion is reinforced in the approved permit in Appendix 2.05.3(4) as