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~~ ~ ~' III IIIIIIIIIIIIIIII ^/~'(/~' Cripple Creek & Victor Gold Mining Company 999 1\ 1\ A Joinl Venture -Pikes Peak Mining Company, Manager ~~~111~/// ~~~../// Operations Office Englewood Oflice PO. Box 191, 2755 State Highway 67 5251 DTC Parkway, Suite 700i~Eq(j~~E Victor, Colorado 80860 Colorado 80111 (719) 669-2977 • FAX (719) 689-3254 (303) 889-0700 • FAX (303) 88 7 ~~ 17 1994 October 11, 1994 Division of Minerals & Geology SENT BY FACSIMILE -HARD COPY FOLLOWS BY MAIL Mr. Berhan Keffelew Environmental Protection Specialist Colorado Department of Natural Resources Division of Mines and Geology Office of Mined Land Reclamation 1313 Sherman Street, Room 215 Denver, Colorado 80203 Reference: Cresson Project: Permit Number M-80-244: Provision of Additional Large-Scale Interface Shear Tests Results Incorporating Carlton Tailing or Goldstar Mine Material With Ironclad Material. Dear Mr. Keffelew: Pursuant to Mr. Sorenson's recommendation, Cripple Creek & Victor Gold Mining Company collected and tested for interface shear a combination of Ironclad Soil Liner material with surficial coatings of (1) Carlton Mill Tailing and (2) Goldstar Mine material. -For the tests, these materials were overlain by 80 mil VLDPE, which was in turn overlain by the Pad k2 material currently being placed as the drain cover. The test results are attached in the form of a letter dated October 10, 1994 from Golder Associates. This letter transmits the draft results of the tests. One additional test using Goldstar Mine material and the final report from the testing laboratory will be transmitted to the Office of Mined Land Reclamation as soon as they are received. The test results demonstrate that the smoothing agents, the Carlton and Goldstar materials, have a negligible affect on the frictional strength of the matrix. While there is a very slight reduction in the internal friction angle, that angle meets the design criterion and the sliding in all but one of the nine cases investigated to date was between the geosynthetic and the drain cover material and not between the geosynthetic material and the underlying Ironclad+smoothing agent. Further, the critical theoretical failure surface in the geotechnical analyses was not that between the geosynthetic and the soil liner but rather the interface between the textured geomembrane and the geotextile. Therefore, Golder concludes that additional stability analyses are not required even though the results of one of the tests indicated a slightly lower interface shear strength that the strength used in the model (23° v. 24°).