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October 28, 2013 <br />To: Marcia Talvitie <br />From: Susan Burgmaier <br />Re: Carbon Junction Mine (Permit No. C- 1992 -080) <br />Technical Revision No. 17 (TR -17) <br />Review of Second Adequacy Response <br />Per your request, I have reviewed the packet provided by Goff Engineering and Surveying, Inc. (Goff) in <br />response to my second round of adequacy concerns with the Technical Revision (TR -17) application for <br />the Carbon Junction Mine. I have the following comments and questions for the operator: <br />1. It is my understanding that Goff has prepared an Appendix 5 -12 to incorporate all of the TR -17 <br />designs, and the remainder of the inconsistencies we identified will be addressed under the permit <br />renewal. Accordingly, this item is resolved. <br />4. Goff revised the design based on a 2.25" value for the 10 yr — 24 hr event, as required by the <br />Division. Goff also determined that predicted velocities would not be high enough to require <br />channel lining, and therefore is not proposing to install rip rap on any of the Upper Carbon Junction <br />channel. There is one segment (43 +00) that indicates that the expected velocity will be 5.37 fps, and <br />several segments that approach 5 fps. Densely vegetated channels can withstand velocities in <br />excess of 5 fps. Mixed grasses typically top out at 5 fps. It is my recollection that the channel was <br />fairly well vegetated. The Division will approve Goff's proposed plan to leave the Upper Carbon <br />Junction in its current configuration, but will advise Oakridge Energy, Inc. that Rule 4.05.3(1)(e) <br />requires all channels to be designed to minimize adverse impacts to the hydrologic balance and to <br />be stable. If it becomes apparent that the channel is not stable, the Division will require Oak Ridge <br />to submit designs for the channel that incorporate channel lining to ensure long term stability. Also, <br />in the event that the Upper Carbon Junction channel is disturbed during reclamation of the berm, <br />channel lining may be necessary until vegetation within the channel is reestablished. <br />S. Goff did not submit a proposed revision to the sixth page of Appendix 5 -2. It is my understanding <br />that this will be addressed under the permit renewal. <br />Should you or the operator have any questions or need additional information, please let me know. <br />