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,~ ~:. <br />~ ~ III IIIIIIIIIIIII III <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Depanmenl of Natural Resources <br />131 J Sherman St., Room 215 II~ <br />Denver, Colorado 80203 <br />Phone: (303) 866-3567 <br />FA%. (303) 832-8106 <br />DEPARTMEM' C <br />NATURAL <br />July 13, 1994 ~S~URCF <br />Mr . John Hardaway Roy Romer <br />Governor <br />Manager Environmental Affairs (amen S. Lochhead <br />Cripple Creek and Victor Gold Eaecurive Director <br />P . (]' $OX 191 Michael B. long <br />V1CtOr, C'~ 80860-0191 Division Director <br />RE: Cresson Mine Permit No. M-80-244. Changes in. Technical <br />Specifications in (1) Durability and Gradation of Underdrain <br />Fill Materials, and (2) Underdrain Configuration. <br />Dear Mr. Hardaway: <br />Dr. James Pendleton and Mr. Allen Sorenson of the Division have <br />reviewed the tensile strength testing that was performed on 27 <br />samples from the second candidate area for the underdrain material, <br />they both agreed that the tests exceed the required value of 300 <br />PSI. Therefore, the Division grants approval of this material for <br />use as the underdrain fill. However, the Division requests the <br />operator visually inspect the material and segregate material that <br />visually fails to meet the necessary requirement for underdrain <br />fill material. <br />The Division also finds the gradation modification for the <br />underdrain material, increasing the maximum size from 8-inch to 12- <br />inch, to be acceptable. However, the Division wishes to remind <br />Cripple Creek & Victor Gold (CC&VG) that if the material as <br />generated from the borrow area does not meet the modified <br />specification, the operator will be required to remove the material <br />from the underdrain and place another material which meets the <br />specification. Further, the increase in maximum material size <br />heightens the importance of a properly installed layer of select <br />backfill material, specified as a 6-inch thick layer of 3-inch <br />minus, to bridge the underdrain material and properly support the <br />12 ounce geotextile and the 80 mil VLDPE fabric. <br />Finally, the Division also approves CC&VG's proposed modification <br />to the underdrain configuration. This configuration change is <br />proposed for implementation in areas of underdrain width less than <br />20 feet. The modification places the three underdrain pipes in a <br />low-flow trickle channel excavated beneath the invert grade of the <br />underdrain pocket. The pipes are bedded and covered in 3/4 inch <br />minus select fill. <br />