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iii iiiiiiiiiiiu iii <br />999 <br /> STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Depanmenl of Natural Resources <br />131 3 Sherman 51., Room 215 <br /> <br />Denver, Colorado 80203 I~~~~ <br />Phune: I]03) 866-3567 <br />FA%:13031 832-8106 <br /> DEPARTMEN'T' OF <br /> NATURAL <br />DATE : May 5 , 19 9 5 '~ ~ RESOURCES <br />TO: Christine Johnston \ Roy Romer <br /> Governor <br />( <br />71 <br /> _1 <br />/, ` <br />j <br />/ <br />lames 5. lorhheaA <br />~ <br />FROM: Jim Pendleton ~ ~ <br />~ <br />K <br />~ ~ F.ec°'iveofre"°` <br /> Michael B. Long <br /> Division Dveaor <br />RE: Mountain Co~al Co ny - Subsidence Report <br /> Mt. Gunnidon 1 Mine (Permit #C-80-007) <br />I have reviewed the semi-annual subsidence report forwarded to you <br />by Kathy Welt of Mountain Coal Company (MCC). This report consists <br />predominantly of a letter report prepared by John Rold for Wright <br />Water Engineers, contractor to MCC. This letter report presents a <br />discussion of a subsidence "crack" near the south line of Section <br />17, in the vicinity of Lone Pine Gulch. <br />John Rold's discussion would be greatly enhanced by the inclusion <br />of a map and supporting cross section sketches of the crack <br />geometry, which he describes in his letter. I must admit, not <br />having examined the crack in the field, to being unclear about <br />John's description. As I understand the situation, John is <br />hypothesizing that the crack, reported to be "5-feet wide" in <br />places, is actually a graben-like wedge of rock which has settled <br />along two pre-existing joints. His suggestion, I conclude, is that <br />the area of the crack lies above a barrier pillar which has had <br />multiple seam mining to the north, and at least single seam mining <br />to its south. The resultant subsidence has resulted in extensional <br />strain being produced in the immediate vicinity of the crack. This <br />extensional distortion may have been accentuated by the close <br />proximity of the steep slope into Lone Pine Gulch, acting as an <br />unconfined free face. <br />If my cursory understanding of John Rold's hypothesis is correct, <br />it sounds plausible. Additional maps and sketches in cross-section <br />would be helpful to clarify John's hypothesis. I should examine <br />the situation myself to draw my final conclusions. Perhaps I can <br />visit the site later this spring or summer. <br />cc: David Herry <br />Doc: M:\MIN\JAP\MTGCRACK.COM <br />JP/JP <br />