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16 September, 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 />michael.cunningham@state.co.us <br />The Union Milling Company <br />P.O. Box 620490 <br />Littleton, CO 80162 -0490 <br />+1.303.947.3499 <br />RE: Leadville Mill; M1990 -057, TR -4; Adequacy Review No.3 <br />Dear Mr. Cunningham, <br />Union Milling Company (UMC) has prepared the following response to Adequacy Review No.3. <br />1. The Division met with Union Milling Company on August 23, 2013 to discuss the remaining <br />adequacy issues of Technical Revision No. 4. As we discussed during the meeting the Division <br />has concerns with long -term structural integrity of the geosynthetic clay liner (GCL) as it related <br />to the seeps on the east side of the tailings storage facility (TSF). The Applicant has <br />demonstrated to the satisfaction of the Division that the GCL can be installed without premature <br />hydration. However, the Applicant must provide additional information which demonstrates that <br />the GCL can withstand external hydrostatic pressure from the seeps. The Applicant may <br />provide any available data from laboratory or field testing from the manufacturer which <br />demonstrates the capacity of the CGL to withstand hydrostatic pressure. <br />Response: <br />Consulting with a hydrogeologist it was determined if there was a failure due to the water <br />flowing from the seep, it would be from fines in the colluvium being washed away, leaving a <br />bulge below the weep and a depression above the weep. <br />Given that the embankment and surrounding material consists predominantly of colluvial <br />materials, the critical gradient of 0.46 is calculated as follows: <br />RECEIVED <br />SEP 16 7013 <br />DIVISION OF RECLAMATION <br />MINING AND SAFETY <br />