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. - • • iii-iiiiiiiiiiiuiii 999 STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Depanmem of NaWral Resources ~~~~ 171 3 Sherman SL, Room 21 5 Denver, Colorado 80203 Phone: 1303) A66-3567 FAX. 1303) 832 B 106 DEPARTMENT OF NATURAL DATE: June 6, 1996 RESOURCES Roy Romer Governor TO: Berhan Keffelew James 5. Lochhead Eaecm rve Dueaor FROM: Allen Sorenson Michael B. Long Division DireUOr RE: Conditions for Approval of Technical Revision TR-020, Cripple Creek and victor Gold Miainq Company, Cresson Project, Permit No. M-80-244 The Operator has committed to complete bench scale testing of soil liner fill materials from all approved borrow areas to characterize freeze-thaw effects on the permeability of the compacted soils. If the bench scale testing demonstrates the potential for significant detrimental freeze-thaw effects, the Operator has committed, and is required, to take appropriate measures to ensure that soil liner fill permeability will continue to meet the design specification of 10_6 cm/sec maximum permeability. The Division cautions the Operator that conformance with the design specification of 10_6 cm/sec maximum permeability for soil liner fill must be demonstrated through direct measurement of in-place density and permeability as detailed in the approved construction quality assurance plan. Further, certification of the facility as constructed in accordance with the approved design plan, in accordance with Rule 7.3.2 of the Hard Rock/Metal Mining Rules and Regulations of the Mined Land Reclamation Board, requires direct measurement to support certified verification by the certifying professional. Therefore, because direct measurement will be precluded by subsequent construction, the Division must be satisfied, based on the results of the bench scale testing, that freeze-thaw effects will not cause an increase in soil liner permeability beyond the 10_6 cm/sec limitation subsequent to the direct density testing of the compacted soil liner. In other words, certification that the soil liner conforms with the design specification of 10_g cm/sec maximum permeability may not rely on indirect demonstrations of rehabilitation of the soil liner fill by post placement consolidation. It is important the bench scale freeze-thaw testing of the soil liner materials be completed expeditiously. The Division encourages the Operator to limit soil liner placement to those areas of the Phase II leach facility which will not be exposed to potential freezing subsequent to compaction until after the results of the bench scale testing have been reviewed and accepted by the Division. Candidate areas would include the pregnant solution storage area and any additional areas which will receive ore placement prior to freeze this fall. If any of the proposed