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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 <br />Phone: (303) 866-3567 <br />FAX: (303) 832-8106 <br />April 5, 2011 <br />Roy Karo <br />Seneca Coal Company, LLC <br />P.O. Box 670 <br />Hayden CO 81639 <br />RE: Seneca II-W Mine (Permit No. C1982057) <br />Technical Revision No. 73 <br />Pond 016 Slide Area Remediation Plan <br />Preliminary Adequacy Review <br />Dear Mr. Karo: <br />COLORADO <br />D I V I S I ON OF <br />RECLAMATION <br />MINING <br />SAFETY <br />John W. Hickenlooper <br />Governor <br />Mike King <br />Executive Director <br />Loretta E. Pineda <br />Director <br />The Division has reviewed your application for Technical Revision No. 73 (TR-73) for the Seneca II-W <br />Mine. We have the following comments and questions regarding the submittal. <br />1. Prior to backfilling Pond 016A, the pond must first be dewatered, and all saturated soils <br />must be removed (NWCC text says "stabilized", but no details are provided) from pond <br />bottom and in-slopes. Please revise the Remediation Plan (page 1 of Attachment 20-D) to <br />include these provisions. <br />2. Standard Proctor curves must be developed for any materials used to backfill Pond 016A. <br />The use of curves developed previously for other SCC projects is not acceptable. <br />3. Given the high clay content of the native materials, and the proposed relocation of Road J/K <br />across the Pond 016A fill, compaction should be a minimum of 95% Maximum Dry Density <br />(NWCC recommends 90%), with a moisture content between 0 and 4% above Optimum <br />Moisture Content (NWCC recommends OMC +/-4%). It is critical that Pond 016A be <br />backfilled and compacted sufficient to prevent, to the extent possible, the infiltration of <br />additional moisture into the fill. Lift thicknesses of 12" to 18" proposed by NWCC may be <br />too great to achieve the desired densities. <br />4. The abandoned wells located at the base of the Pond 016A embankment were damaged in <br />the original slide (May 2003) that occurred at the inlet and access road to Pond 016. The <br />slide bent and in some cases broke the casings below ground surface (about 40' bgs). After <br />SCC consulted with Halliburton on-site, service rigs and drill rigs were employed to try and <br />Office of Office of <br />Mined Land Reclamation Denver • Grand )unction • Durango Active and Inactive Mines