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STATE OF COLORADO AICH~D. L~. +ov r.mrv ^III III III III IIII III <br />DEPARTMENT OF NATURAL RESOURCES <br />Harris D. Sherman. Executive Director <br />MINED LAND RECLAMA'T'ION <br />423 Centennial Building, 1373 Sherman Street <br />Denver, Colorado 80203 Tel. (303) 839-3567 <br />David C. Shelton <br />Director <br />October 2, 1980 <br />TO: Carol Pahl ke 1 )ff^~~ <br />FROM: Jim Pendleton <br />RE: Request r Auge fining Amendment with Decreased Rib Thickness at <br />Delagua fine <br />I have reviewed TBM's request, as forwarded by their consultants, Mineral <br />Resources and Engineering, Inc. I have also discussed this request with <br />Rick Mills and Darry Ferguson of Mineral Resources and Engineering, Inc., <br />in person. <br />Their plan will conform with the Colorado permanent regulatory section <br />4.23 with one minor rrodification. The U.S. Bureau of Mine's open file <br />report no. 108-76, dated October, 1975, is entitled "Technology of <br />Auger Mining". I have attached, for the applicant's edification, copies <br />of figure 9f and pages 75 through 78, entitled "Auger Safety" of that <br />publication. Basically, these sections observe, among other things, <br />that if rib thickness is inadequate, dangerous and environmentally damaging <br />highwall failures, landslides, and subsidence may occur. These occurances <br />are both hazardous to the operator's safety and may result in pit backfill <br />and/or highwall instability. Collapse of the angered seam can result in <br />subsidence of the previously undisturbed slope areas above the highwall. <br />This can result in a creation of tension cracking and impoundments, both <br />contributory to increased infiltration and backfill or slope instability. <br />For this reason, I forward the following recommendations for your consid- <br />eration: <br />1. The minimum rib thickness should be stipulated at 6". The Kentucky <br />experience referred to in the applicant's request probably deals with <br />stronger, higher-grade coals. The Bureau of Mine's specifically recommends <br />in figure 9f, rib thickness of 1/6 the seam thickness (12" in Delagua's <br />case, as originally stipulated in the approval). Furthermore, the BLM <br />report discourages rib thicknesses of less than 6". <br />2. As the applicant's request proposes, if a minimim rib thickness of <br />6" proves to be inadequate, the experimental program should increase <br />(cont'd.) <br />