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iii iiiiuiiiiiiiu <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: 17031 866-3567 <br />FA%: (3031 832-8106 <br />DATE: February 9, 1995 <br />T0: Erica Crosby <br />FROM: Jim Pendleton 5 <br />RE: Roadside rtal <br />ermlt <br />/-. <br />/. <br />4i~ies - Subsidence Concerns <br />No: C-81-041) <br />~I~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Roy Romer <br />Governor <br />lames S. LOChhead <br />Eaecutrve Director <br />Michael B. Long <br />Divrsion Director <br />I have completed a review of the limited materials which you forwarded to me <br />concerning the Roadside North Portal Mine. 1 do have a general concern regarding <br />the subsidence monitoring requirements placed upon the North Portal Mine. <br />From 1980 through 1990 I had a fairly frequent involvement with the Roadside <br />mine, including issues mainly related to subsidence and the waste piles. The <br />Roadside Mine had a fairly extensive subsidence control plan because of the water <br />treatment plant, water collection pipelines, an electric transmission line, roads, <br />and Rapid Creek. Each of these features had subsidence control plans and <br />subsidence monitoring requirements. The subsidence monitoring requirements <br />included extensive arrays of survey monuments and periodic visual inspections of <br />the surface, with specific attention focused upon Rapid Creek. <br />A great: deal was learned about the mechanics of subsidence in the Williams Fork <br />Formation and the Mesa Verde Group rocks at the Roadside Mine permit area. <br />These observations have allowed the development of fairly confident values for <br />the angle of draw and vertical subsidence magnitude at the mine site. Because of <br />the similarities in stratigraphy, mine plan, surface topography and surface <br />hydrology, much of this information should be useful in the preparation of the <br />subsidence inventory and subsidence control plan for the North Portal Mine. <br />The information you provided very briefly states on page 225: "There are no <br />structures or renewable resource lands with potential for adverse affects from <br />subsidence in the Roadside North Portal mining area." Having examined the map <br />