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AVCOLORADO <br /> Division of Reclamation, <br /> I Mining and Safety <br /> i <br /> i Department cf Tia`_rs Rest.-c- <br /> 1313 Sherman Street, Room 215 <br /> Denver, CO 80203 <br /> Date: July 29, 2016 <br /> To: Michael Cunningham <br /> From: Tim Cazier, P.E. <br /> RE: Schwartzwalder Mine, DRMS File No. M-1977-300; <br /> Preliminary Adequacy Review - TR-23, Waste Rock Pile Engineering Review <br /> The Division of Reclamation, Mining and Safety (Division) engineering staff has reviewed <br /> Appendix E-3 (original submittal) and E-4 (responses) from the 1983 Mine Permit <br /> Amendment related to the Waste Rock Pile Stability as submitted in Technical Revision <br /> No. 23 (TR-23). The following comments are posed to ensure adequate engineering <br /> analyses and design practices are implemented to eliminate or reduce to the extent <br /> practical the disturbance to the hydrologic balance expected by the mining operation <br /> with respect to water quality and quantity in accordance with Rules 3.1.6(1), 6.4.7, <br /> and 7.3.1; and slope stability in accordance with Rule 6.5. <br /> Stormwater - Text: <br /> 1 . Pap <br /> e 51, Small Gulch Energy Dissipator. Apparently the previous plan was to <br /> collect runoff from the small gulch above the East Waste Rock Pile and discharge <br /> it through a spillway causing it to spread out into sheet flow over the waste rock <br /> pile. This concept will not work. The waste rock piles are considered <br /> environmental protection facilities (EPFs). As such, stormwater must be diverted <br /> around the waste rock piles in channels designed to convey the peak discharge <br /> resulting from the 100-year, 24-hour design precipitation event. <br /> 2. Page 52, Section 7.2.2. This section states riprap is sized and gradation provided <br /> on Sheet 3 of 5. No such information could be found on Sheet 3 <br /> Stormwater - Drawings (Sheets 1 through 5): <br /> 3. Sheet 3. The features labeled as "Sheet Runoff energy Dissipators" must be re- <br /> designed as stormwater diversion channels with the capacity to safely convey <br /> the peak flow from the 100-year, 24-hour design precipitation event, with <br /> adequate freeboard. This channel design should include depth (with freeboard), <br /> side slopes, bottom width, riprap size and gradation. <br /> oF'co <br /> 1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mimng.state.co.us <br /> John W. Hickentooper, Governor 1 Robert Randall, Executive Director I Virginia Brannon, Director *\" <br />