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Doug White, Western Fuels <br />C- 2010 -089 TR -01 PAR <br />Mar. 11, 2013 <br />Page 2 of 9 <br />6, 2012 indicate that the primary spillway is a drop inlet riser at 5675.5' with two 6" <br />gated weep holes at 5671.5'. Since these weep holes are gated, two designs should be <br />run - one assuming the gates are fully open to determine whether runoff from the design <br />event will meet the effluent standard in the event that the gates are open when a major <br />storm occurs (Rule 4.05.6(3)(a)), and another assuming the gates are fully closed to <br />ensure that the primary spillway is sized to treat and convey the design runoff without <br />discharge through the emergency spillway (Rule 4.05.9(2) (b)) in the event that the gates <br />are in the closed position when a major storm occurs. The rationale for this modeling <br />methodology is also explained in Appendix 2.05.3(4) -1 of the New Horizon North permit <br />application package, beginning on page 4. <br />WFC: SEDCAD run evaluations for the following four cases, including I Oyr -24hr event <br />with 2 — 6" weep holes wide open and weep holes closed, and 25yr -24hr event with 2 — <br />6" weep holes wide open and weep holes closed were run and the results are included <br />with this application. In both 10yr -24hr and 25yr -24hr precipitation event cases where <br />the weep holes are fully opened, the settleable solids concentration discharge is less than <br />the 10yr -24hr event effluent limit of 0.5 ml /1. All four SEDCAD run cases, including <br />weep holes closed, result in no discharge through the emergency spillway. <br />DBMS: Response accepted, but we have additional comments — see new item 8, below. <br />2. DBMS: The as -built designs for pond NHN -001 include a revised Eroded Particle Size <br />Distribution (EPSD), labeled "New Horizon Mine 1 ". This EPSD differs from the <br />previously approved EPSD for NHN -001, and is also dissimilar to any of the EPSDs in <br />the approved New Horizon Mine 1 and 2 designs also labeled "New Horizon Mine V). <br />Please explain the basis for this distribution. If this particle distribution is based on site <br />soil samples, please provide a copy of the laboratory report used for the distribution. <br />WFC: The EPSD in the four SEDCAD runs included with this application has been <br />revised to match the previously approved EPSD for Pond NHN -001. <br />DBMS: Response accepted. <br />3. DBMS: Page 5 of section 2.05.3(4) of the approved permit application package notes <br />that mine water, at a rate of 1 -2 cfm, may be pumped from the pit to Pond 001, 002, or <br />003. This pit water inflow does not appear to be accounted for in the SEDCAD design, <br />as required by Rule 4.05.6(3)(a). Please either revise the SEDCAD design to include this <br />base flow /permanent pool (Rule 4.05.9(2)), or state that pit pumping will only occur <br />when the sediment pond is at or below the weep hole elevation and that the pond will be <br />dewatered within 24 hours. It should be clear that in no case will pit water pumped into <br />the pond result in the passage of runoff from the 10 -year 24 -hour event through the <br />emergency spillway (Rule 4.05.9(2)(b)). <br />WFC: All four SEDCAD run cases included with this submittal were run using a <br />designed null structure #1 with watershed information set to simulate approximately 2 cfs <br />