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-- ._ ST4TE O!- CUI ~-~:, .:^C u., ..:,5n a n~. ...~,.~ <br />D EPARih'IE VT OE N4TUN4l RESOVmCES <br />tl~vr Dvru or <br />~ Harms D Sn rrman. L.e rr <br />`,r ji <br />' '#' :191'~ED L.1\U RI?l:I~:111~1'1'~O'~ <br />/ 4. V• ~ - \ <br />~,..~ ~ ,u~~. _ `?~ 423 Centen nial fi Viihiny 1313 Sherm an Stre^t <br />"'~~' .J~-~;~~~ Denver. Golo raao 60203 TeL (303) 839-3567 <br />~~ <br />David C. Shetlon <br />Director <br />October 2, I080 <br />T0: Carol Pahlke _~ <br />1 <br />FROFI: Jim Pendle~nn ~ - __ ~~`~-~~~ ` ~~~~~ <br />RE: Request for Auyet Mining Amendment with Decreased Rib Thickness at <br />Delagua Coal ,nine <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 Mi11s and Darty Ferguson of Mineral Resources and Engineering, Inc., <br />in person. <br />Their plan will conform with the Colorad: permanent regulatory section <br />9.23 with ore minor rrodification. The U.S. Bureau of Mine's open file <br />report no. 108-7b, dated October, J375, 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 thick:~ess is inadequate, dangerous and environmentallu 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 tine highwall. <br />This can result in a creation of tension cracking and impoundments, both <br />contributory to rrrcreased 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 rrrquest probably deals with <br />stror:ger, ttigl~er-r/rade teals. Tl~e Bureau oI Mine's specifically recomm.~~nds <br />in Figure yf, rib thickness of I/6 the seam thickness (12" in Delagua's <br />case, as originally stipulated in the approval). Furthermore, the 8LM <br />report discourages rib thicknesses of less than 6". <br />... As the appIicant's request proposes, if a .minimim rio thickness of <br />6" proves t_o be inadequate, the experimental program should increase <br />(cont'd) <br />' ~II <br />a <br />I <br /> <br />,M <br />~. <br />~" c3 U <br />