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1 <br />STATE OF COLORADO <br />DIVISION OF RECLAMATION, MINING AND SAFETY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 866-3567 <br />FAX: (303) 832-8106 <br />INTEROFFICE MEMORANDUM <br />Date: 16 February 2010 ReCe%vED <br />To: Jim Stark, Lead Specialist 8 9 2010 <br />F?,. dot Kec?amadon, <br />on, <br />From: Marcia L. Talvitie, P.E. est <br />Subject: Colowyo Mine - Permit No. C-1981-019 <br />TR-81 - South Taylor Excess Spoil Fills <br />Adequacy Review - Geotechnical <br />COLORADO <br />D I V IS I ON OF <br />RECLAMATION <br />MINING <br />SAFETY <br />Bill Ritter, Jr. <br />Governor <br />Harris D. Sherman <br />Executive Director <br />Ronald W. Cattany <br />Division Director <br />Natural Resource Trustee <br />I have reviewed the application for TR-81, as you requested on 29 December 2009. The revision <br />seeks approval for increasing the volume of two excess spoil fills that have been previously <br />approved. In addition to increasing the capacity (and area) of these fills, Colowyo proposes to <br />steepen the outslopes and temporarily store large quantities of excess spoil on top of the fills. <br />Two major issues have been considered in this review: 1) the postmining topography proposed, <br />as it relates to approximate original contour and excess spoil, and 2) the proposed configuration <br />of the temporary and permanent excess spoil fills. <br />My comments regarding the Geotechnical Study are presented separately from the PMT / AOC <br />issue. The primary issue for the Division to determine is whether or not the post-mining <br />topography proposed by Colowyo meets the requirements of the Regulations. There are several <br />locations where the proposed post-mining topography is at a lower elevation than that which has <br />been previously approved by the Division. I respectfully suggest that we may also wish to revisit <br />some of the topography previously approved, as there are certain areas where the approved <br />elevations are lower than what existed pre-mining. With a swell factor of 15% to 20%, it seems <br />that all areas should be backfilled and graded to at least the original elevations. Excess spoil, by <br />definition, is limited to those volumes that are not necessary to achieve AOC. <br />The TR-81 application does not clearly delineate the changes proposed. Following a comparison <br />of the TR-81 cross sections with the versions previously approved, I make the following <br />observations: <br />• Map 20, Section B-B' - TR-81 is proposing a change from Station 15000 to 17000 - <br />lowering the post-mining topography (PMT) by up to 180'. <br />• Map 20A, Section E-E' - TR-81 is proposing a change from Station 15500 to 18000+, <br />lowering the PMT by up to 180'. <br />• Map 20B, Section A-A' - The PMT in the eastern (right-hand) portion of this section is <br />below the pre-mine elevations, but higher in the west. <br />Office of <br />Office of <br />Mined Land Reclamation Denver • Grand )unction • Durango Active and Inactive Mines