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a <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 C O L D RA D O <br />Denver, Colorado 80203 DIVISION O F <br />Phone: (303) 866-3567 MIN &RA L S <br />FAX: (303) 832-8106 G E O L O G Y <br /> 0.EClAMATION~M WING <br /> SAFFTT•SCIENCE <br />DATE: August 5, 2003 <br /> Bill oven: <br />/ Governor <br />TO: V Jim Burnell Greg E. Watcher <br /> Executive Director <br />n Ronald W. Cattany <br />FROM: Joe Dudash r+~ ~ Division DireROr <br />U Natural Resource Trustee <br />RE: Elk Creek Mine, Permit No. C-1981-022, Oxbow Mining <br />Technical Revision No. 43, Gob Pile IIW <br />I have finished my review of the TR-43 submittal from Oxbow. In general, the Sedcad <br />designs were well done. All of the design parameters that were used were reasonable in <br />nature and had been approved in previous revisions. My questions and comments follow. <br />I believe that the issues in my questions numbered 9 through 12 also appeaz in Byron's <br />TR-43 memo. <br />In the Section 8 culvert sizing table for the IIW culverts, there is a footnote that <br />states that "IIW is designed to pass the peak flow from a 100 year, 24 hour event". <br />However, the peak flows used for IIW culvert 1 and IIW culvert 3 appear to be <br />from the 10 yeaz, 24 hour event. Please revise the footnote, if appropriate. <br />2. In the Section 8 culvert sizing table for the IIW culverts, culvert IIW-3 receives <br />flow from the West Valley Diversion, which is a ditch designed for the 100 year, <br />24 hour event. However, it appears that the culvert is designed using the 10 year, <br />24 hour event. Please explain or revise the culvert design. <br />3. In the channel design table for the II West Coal Refuse Facility, there is a <br />footnote that states "Flows for II West channels based on the 100 year/24 hour <br />storm". However, the bench channels and IIW HR (Upper) and IIW HR (Lower) <br />are designed using the 10 yeaz, 24 hour event. Please clarify the footnote. <br />4. The Division's copy of the TR-43 submittal contains two different Sedcad design <br />runs for the clean water diversion ditch. The first run resulted in a peak flow of <br />10.66 cfs, while the second design run resulted in a peak flow of 11.89 cfs. Please <br />explain. <br />Please provide the Sedcad hydrology designs for IIW culvert 4. <br />Office of <br />Mined Land Redamadon <br />Office of <br />Active and Inactive Mines <br />Colorado <br />Geological Survey <br />