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• <br />s <br />r <br />• <br />MEMO: <br />TO: Dr. Kohl <br />FROM: C.E. Gerity ~4h.~-/~ <br />DATE: May 16, 1995 <br />SUB~7ECT: Subsidence Over Limited Extraction Room and Pillar Mining at the <br />Allen mine. <br />On Friday May 12, 1995, I visited with Jack Snow ,the retired Mine <br />Superintendent of The Allen mine. Mr Snow is an Engineer and was employed by <br />CF&I during the time of the Woodward-Clyde study. He recalled the study, and said <br />there had been no other studies of the mines while he was there. <br />Some of the points that he made while talking to him were: <br />The Woodward- Clyde methodology and procedures were very good, He would <br />not challenge the survey data. <br />The Allen mine had serious problems with faulting and roof falls. The room and <br />pillar panel in the Woodward-Clyde study was one of those areas. To be able to <br />manage this problem in this section and in many other sections of the mine, they <br />would typically use a mining technique that he referred to as development, a <br />room and pillar system with narrow openings, to follow the coal. There was no <br />retreating and the extraction was limited. <br />Some of the room and pillar sections with development mining subsided. The <br />most notorious was a opening along the State highway. (Several local residents <br />had told me of this problem, but I did not know that it was over a room and <br />pillar limited extraction section) <br />• He said there were many failures in the mine that effected the surface along the <br />Purgatoire River valley, and that they were very concerned at the time. These <br />were all over limited extraction room and pillar areas. He indicated that the <br />surface expressions are subtle and an observer would have to know the mining <br />areas to make the connection. <br />On Monday May 15 I was able to review and have copies made of some of the mine <br />maps of the Allen mine that are on file with the state. <br />Map A includes the section just to the west of Section 2 South, from this it is clear <br />that Figure 3.2 in the Woodward-Clyde report actually indicates the final mine <br />configuration. You are correct in noting that surface monument 3-1 lies over a <br />s-:ction that was mined out probably using a retreat system. However all of the <br />other points overlie either entries with wide pillars, limited extraction development <br />mining with wide pillars, or no extraction at all. If a line were drawn from the edge <br />of the retreat mining area at a conservative angle of influence of 35° it would <br />intersect the ground surface at about monument 3-8. Measurable significant surface <br />movement occurs to east of this monument, that can only be attributed to <br />excavation in room and pillar areas with wide pillars. <br />PIONEERING ENGINEERING 6505 Su. Allreun Sf. <br />CONSULTING ENGINEERS Gltldnn. C080I23 <br />,17mi y ~ Eno4onnvnie/ } G.a/ ~Qi/ 979-2351 <br />