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May 14, 2013 <br />Mr. Michael Cunningham <br />Environmental Protection Specialist <br />Division of Reclamation, Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />� V" <br />Re: Permit M1990 -057, TR #4 Revision <br />Dear Mr. Cunningham, <br />TR �., <br />6,,4he Union Milling Company <br />PO Box 620490 <br />Littleton, CO 80162 <br />+1.303.9473499 <br />RECEIVED <br />MAY 16 2013 <br />Division of Reclamation, <br />Mining & Safety <br />Union Milling Company (UMC) is providing the enclosed Technical Revision (TR4) revising <br />Permit M 1990 -057 to reconstruct an existing tailings storage facility (TSF). <br />The previous TR, TR3, specified a clay liner be installed between the impoundment sub -base <br />and leak detection system. Construction of the impoundment embankment revealed that <br />insufficient on -site clay material existed within the current impoundment area to construct the <br />clay liner. TR4 is a material change request to replace the clay liner construction material with a <br />geosynthetic clay liner (GCL) of equivalent or better protective values. The GCL material <br />change subsequently requires a material change in the overlying leak detection material and <br />construction, also with equivalent or better protective materials. Lastly, a seasonal perched <br />aquifer was encountered during embankment construction approximately 4 ft from the floor on <br />the east side of the TSF. This TR outlines three progressive methods the liner contractor may <br />employ to install GCL material over the seep and maintain the GCL integrity. <br />The TR includes text changes to 17 pages of the September 27, 2011, TR3. The 17 pages are <br />submitted as replacement pages and marked as May 14, 2013. Additionally, a courtesy copy of <br />the replacement pages with track changes is provided for the Division to readily identify the <br />changes. Exhibit TSF -05, Tailings Storage Facility Phase 1 Leak Detection has been modified <br />and Exhibit TSF -06, Tailings Storage Facility Details is a new Exhibit. Both Exhibits are signed <br />by a Colorado Registered P.E. and P.L.S. and are included with the TR submittal. <br />This TR is for an active 110d permit and in accordance with Rule 1.5.3, a fee of $1,006 is <br />enclosed for the TR submittal. <br />v <br />