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w <br /> ~~I II~~~~I~~II~~ ~~~ <br />sss <br /> STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />F~CO <br />Department of Natural Resources ~4 <br />~O <br />ti~.'i <br />~ <br />1313 Sherman St., Room 215 <br />~ ~ <br />Denver, CO 80203 <br /> <br />Phone: (3031866-)567 ra 5 • <br />FAX: (303) 832-8106 - <br /> Roy Romer <br /> Governor <br /> Michael B. lonti <br /> Division Dvec br <br />DATE: January 31, 1994 <br />TO: Steve Shuey <br />FROM: Christine Johnsto <br />RE: Technical Revision No. 18; Bear Mine; Permit No. C-81-033 <br />Per your request I have reviewed the revised hydrology calculations <br />for the Bear #3 Mine. I have the following comments for your <br />consideration: <br />1. Culverts #4 and #5 were eliminated from the drainage plan <br />as they are no longer functional. <br />2. Boundaries for areas #4, 5, and 7 changed. <br />3. I reviewed the peak flow calculations table on page 11-3 <br />and found that although some of the input parameters <br />differed from the previous table, the adjusted peak flow <br />is not highly variable from previous values and should <br />not make a major difference in the sizing of culverts and <br />ditches and the pond. <br />4. I did model some of the areas on SEDCAD and discovered <br />that the method used by Jim Stover is much more <br />conservative than SEDCAD. I have enclosed the output for <br />your information. <br />5. I reviewed all culvert sizings and found them to be <br />adequate, with the exception of Culvert #3. The operator <br />does state that the culvert is slightly undersized, but <br />overflow from the 10-year event would flow across the <br />road and into the mine bench access road collection <br />ditch. It appears that this would be true. However, <br />knowing that this ditch requires cleaning on a monthly <br />basis, I would strongly recommend that this 8" culvert be <br />replaced with a 12" culvert. In addition, it would <br />decrease Bear's potential for a possible enforcement <br />action, if the water did not end up in the road ditch and <br />flowed off-site. Or an enforcement action would be <br />probable if the capacity of the 8" culvert was decreased <br />with sediment. <br />