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<br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br /> <br />1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us <br />John W. Hickenlooper, Governor | Robert Randall, Executive Director | Virginia Brannon, Director <br /> <br /> <br />December 1, 2016 <br /> <br />Mr. Jack Henris <br />Cripple Creek & Victor Gold Mining Company <br />100 N. Third Street <br />P.O. Box 191 <br />Victor, CO 80860 <br /> <br /> <br />Re: Project, Permit No. M-1980-244; <br /> Technical Revision (TR-86) Preliminary Adequacy Review <br /> <br />Dear Mr. Henris: <br /> <br />On November 28, 2016 the Division of Reclamation, Mining and Safety received a request for a <br />Technical Revision (TR-86) addressing the following: <br /> Globe Hill Stormwater Diversion Channel <br />The submittal was called complete for the purpose of filing on November 28, 2016. The decision <br />date for TR-86 is December 28, 2016. Please be advised that if you are unable to satisfactorily <br />address any concerns identified in this review before the decision date, it will be your responsibility <br />to request an extension of the review period. If there are outstanding issues that have not been <br />adequately addressed prior to the end of the review period, and no extension has been requested, the <br />Division will deny this Technical Revision (TR). <br /> <br />The following comments are based on the Division Engineer’s review of the request for TR-86: <br />1) Hydrologic Analysis. The second paragraph under “Stormwater Design” on the second page <br />of the TR request states “the total watershed contribution is 74 acres”, and that a conservative <br />“0% infiltration” approach was used to estimate a 100-year, 24-hour peak flow runoff of 11 <br />cfs. The Division performed a rough check of the peak flow and the contributing area. The <br />peak flow was check using the SCS (now NRCS) March 1984 “Procedures for Determining <br />Peak Flows in Colorado” Figure S-1A (see Attachment A). Assuming a SCS curve number <br />(CN) of 90, low infiltration, but not zero, the peak flow was estimated to be 218 cfs. An <br />additional peak flow estimate was done using a more moderate CN of 70, which resulted in a <br />peak flow estimate of 66 cfs. The Division estimated the contributing watershed area using <br />Google Earth Pro with a USGS map overlay (see Attachment B). This showed a contributing <br />area of approximately 128 acres. <br />a. Please double check your runoff analysis and provide the Division with calculations <br />demonstrating the 11 cfs (or revised) peak flow estimate. Please be aware that the <br />diversion channel needs to be designed for the worst case runoff condition, which is