1992-02-10_GENERAL DOCUMENTS - C1981017 (2)

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Memo to Candace Thompson Re: Coal Basin Mines - Subsidence page 4 CALCULATED SUBSIDENCE RATIOS (Continued) (Revision of Table 2 - December 1985 Report by Dr. Collins ) Point Total Total Coal Subsidence Number Subsidence Removed Ratio MC-1 - 8.00' - MC-2 -3.49' 8.00' 0.44 MC-3 -2.64' 8.00' 0.33 MC-4 -4.07 ' 16.00' 0.25 MC-5 -0.90' 8.00' 0.11 MC-6 -0.32' 8.00' 0.04 MC-7 - 10.00' - MC-8 - 0 - MC-9 -0.62' 8.00' 0.08 MC-10 -2.58' 10.00' 0.26 MC-11 -1 .98' 10.00' 0.20 MC-12 -1 .31 ' 10.00' 0.13 MC-13 -1 .03' 10.00' 0.10 MC-14 -0.87 ' 10.00' 0.09 MC-15 -0.93' 10.00' 0.09 MC-16 -0.73 10.00' 0.07 Based upon this very brief recalculation of subsidence factors, it is my conclusion that significa t residual subsidence has occurred following the 1985 subsidence monument urvey. Preliminarily, it appears that the actual subsidence factor is appr ximately 0.45, rather than the 0.30 calculated by Dr. Collins following the 1985 subsidence monument survey. I assume that a similar recalculation of he observed angles of draw might also determine them to vary from the 1985 con lusions. Compliance with St i pul ati bn (4) Because double-pass longwall extraction has not been resumed at the Coal Basin Mines, the operator has not been required to resume subsidence monitoring. In the event that double-pass longwall extraction is initiated the Division will require Mid-Continent Resources to resume an appropriate monument surveying subsidence monitoring program. Conclusion I recommend that the Division accept MCR's recently submitted subsidence reports. Further, I reconmend that you approve renewal of the subsidence-related aspects of the permit with the following stipulations. (1 ) Mid-Continent Resources shall complete an annual visual subsidence inspection of the area above the Coal Basin Mines which could