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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 D O L OI R ON o? <br />Phone: (303) 866-3567 RECLAMATION <br />FAX: (303) 832-8106 MINING <br />INTEROFFICE MEMORANDUM SAFETY <br />Bill Ritter, Jr. <br />Governor <br />Date: 14 July 2010 James B. Martin <br />Executive Director <br />Loretta E. Pineda <br />To: Jim Stark, Lead Specialist Director <br />From: Marcia L. Talvitie, P.E. 7bl. <br />Subject: Colowyo Mine - Permit No. C-1981-019 <br />TR-81- South Taylor Excess Spoil Fills <br />Second Adequacy Review - Geotechnical <br />As requested, I have reviewed Colowyo's 1 June 2010 response to the Division's Preliminary Adequacy <br />Review (PAR) for TR-81. With this response, there have been substantial changes made with respect to <br />the proposed Postmining Topography (PMT), and the Shannon & Wilson Report (Exhibit 21) has been <br />revised to address the Division's comments. <br />For my review, I have rearranged the order of my original comments to correlate with the numbering <br />system used in the Division's PAR and in Colowyo's adequacy response. The number which itemized <br />my original comment is in parentheses, and follows the PAR designation. <br />1(7) Section 2.05.3(6)(c) lists the requirements for the geotechnical investigation of a proposed <br />disposal site. Bedrock characteristics; adverse geological conditions; locations of springs and <br />seeps; and rock drain material characteristics have been successfully addressed in previous S&W <br />studies for the South Taylor area. With respect to (iii), potential effects of subsidence, S&W <br />issued an opinion in Addendum No. 2 (Nov-2008) that highwall mining will not significantly <br />affect spoil foundation conditions and should not reduce the global stability of the spoil fill. <br />With TR-81, the dimensions (lateral and vertical) of the temporary and excess spoil fills have <br />been enlarged. The issue of potential subsidence has not been addressed in the Oct-2009 S&W <br />study. Please address the potential effects of subsidence of the subsurface strata due to highwall <br />mining activities, considering the proposed configurations of permanent and temporary excess <br />spoil fills. <br />The potential effect of subsidence due to highwall mining has been addressed on Page 6 of <br />Addendum No. 3 to the Shannon & Wilson study (revised April 15, 2010). This item is <br />resolved; no additional response is required. <br />5(10) Map 19B - Postmining Topography- South Taylor Area <br />a) Please add stationing tick-marks to the cross sections. <br />Tick-marks have been added. Item resolved. <br />Office of Office of <br />Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines