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February 20, 2013 <br />To: Marcia Talvitie <br /> <br />From: Susan Burgmaier Re: New Horizon North Mine (Permit No. C-2010-089) <br /> Technical Revision No. 1 <br /> Preliminary Adequacy Review <br /> I have completed my review of the responses provided by Western Fuels-Colorado (WFC) to my adequacy concerns stemming from Minor Revision No. 2, resubmitted as <br />Technical Revision No. 1 (TR-1), providing the Pond 001 As-Built design at the New <br />Horizon North Mine. I have the following comments: <br /> 1. DRMS: The designs (SEDCAD runs) submitted for the NHN-001 pond as-built indicate that the primary discharge structure is a perforated riser, with 2” holes at <br />the 5671.5’ elevation. Map 2.05.3(4)-6 and the photographs provided by the <br />operator on December 6, 2012 indicate that the primary spillway is a drop inlet <br />riser at 5675.5’ with two 6” gated weep holes at 5671.5’. Since these weep holes are gated, two designs should be run - one assuming the gates are fully open to determine whether runoff from the design event will meet the effluent standard in <br />the event that the gates are open when a major storm occurs (Rule 4.05.6(3)(a)), <br />and another assuming the gates are fully closed to ensure that the primary <br />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 <br />methodology is also explained in Appendix 2.05.3(4)-1 of the New Horizon North <br />permit application package, beginning on page 4. <br /> WFC: SEDCAD run evaluations for the following four cases, including 10yr-24hr <br />event with 2 - 6” weep holes wide open and weep holes closed, and 25yr-24hr <br />event with 2 - 6” weep holes wide open and weep holes closed were run and the <br />results are included with this application. In both 10yr-24hr and 25yr-24hr <br />precipitation event cases where the weep holes are fully opened, the settleable solids concentration discharge is less than the 10yr-24hr event effluent limit of <br />0.5 ml/l. <br /> <br /> All four SEDCAD run cases, including weep holes closed, result in no discharge <br />through the emergency spillway. DRMS: Response accepted, but we have additional comments - see new <br />item 8, below. <br /> <br />2. DRMS: The as-built designs for pond NHN-001 include a revised Eroded Particle Size Distribution (EPSD), labeled “New Horizon Mine 1”. This EPSD