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• <br />•, <br />Page 2 <br />Carol Pahlke <br />October 2, 1980 <br /> <br />rib thicknesses by increments of 2" until a stable thickness is determined. <br />3. The applicant's consultant should observe and report to the Division <br />the results of the experimental program. <br />y, As recommended in the Bureau of Mine's report, we should require the <br />applicant, during their proposed experimental program to determine rib <br />thickness, to carefully monitor the condition of the ribs with time. <br />Particular concern should be focused upon any evidence of rib coal cracking <br />or spoiling. In order to monitor the rib condition, the initial auger <br />holes will have to remain unbackfilled for several weeks. This should <br />not, however, offend the thirty day prohibition included in Colorado <br />permanent regulatory section 4.23(4). Furthermore, the applicant should <br />monitor, via appropriately placed survey cross sections, the slope <br />stability above the highwall within initial augering sections of the <br />pit. <br />s. It should be stipulated that prior to bond release the areas above the <br />highwall overlying augering bores will be re-inspected to discern subsidence <br />effects. The applicant should be responsible for correcting any subsidence <br />impoundments or other materially detrimental subsidence effects which <br />occur, prior to bond release. <br />Jim <br />/k <br />encl. <br />