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III IIIIIIIIIIIIIIII 999 STATE OF COLORADO DIVISION OE MINERALS AND GEOLOGY Dcpanment of Nawral Resources ~~~I~~~~~ 1313 Sherman St., Room 215 Denver, Color, do R0203 Phonc: (303) 866-3567 FA%: (3031 R32-R106 DEPARTMENT OF DATE: February 9, 1996 RESOURCES Roy Romar TO: Barbara Pavlik envemor FROM: Susan Burgmaier~ lames s. E~hhe.,a Executive Director RE: North Thompson Creek Mines (C-81-025) Michael e. EotiR Divisian Director Midterm Review I have finally completed my portion of the North Thompson Creek Mines Midterm Review. I apologize for the delay, and appreciate your patience. You asked me to complete the portion of the review pertaining to surface water, ponds, impoundments, diversions, and alluvial valley floors. I reviewed the applicable sections of the permit application package, pertinent revisions since the permit renewal, 1993-1995 inspection reports, and 1993-1995 AHR's; and talked to Larry Routten. As a result, I have one concern for your consideration. Talking to Larry, I became aware that the ditch (D-7 and D-6) along the county road had failed after a storm event. This is the ditch that diverts runoff from the refuse area, along the road, and then over the mine area. Modifications to the ditch were required to abate a notice of violation (NOV). I tried to figure out, reading the inspection reports, why the ditch might have failed, and came up with a few possibilities. They are: 1 - The storm event might have been in excess of the 10-year, 24-hour event, which is the event for which the D-6 portion is designed. 2 - The ditch and check dams might not have been constructed as designed. 3 - Replacing the sumps with check dams may not be suitable; additional or alternate energy dissipation is required. I don't have any way of verifying the storm size, I don't know if the ditches were properly constructed (no measurements noted in inspection that terminated NOV), and I'm not ready to throw out the check dam idea. However, I think we need to figure out what the problem was, to ensure it does not happen again. In order to do that, I think we should start by verifying the construction of the ditches. As soon as the snow is off, we need to compare what's in the field to what we approved (Appendix 4-B, Volume III), and get them reworked if necessary. We'll need to verify ditch dimensions and grade, and the location, dimensions, and substance of the check dams. With the ditches and check dams as designed, we can see how it functions this summer. If they are not working, we'll probably have to revisit the design. , I have no other concerns with ponds, impoundments, or diversions, nor were any raised regarding surface water information or alluvial valley floors. If you have any questions, let me know. c: Larry Routten SLn\@0996. W P