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SErff BY= ~-95 ;11=13PM 0 S. 303 832 8106:# 6/ g of draw increase with the increase in extraction thickness, extraction ratio, and with a decrease in the percent of hardrock in the overburden. As our original calculations indicate, using the actual extraction ratio, extraction thickness, and percent hardrock from the geological maps, subsidence would not occur. In order to obtain an angle of draw of 34.52 degrees, we had to double the extraction thickness (to 15 feet), half the percent hardrock (to 15$) and assume 100$ extraction (versus 31$). The calculations are shown on the attached computer printout. As you can see even with this theoretical situation, the subsidence would not reach your house (644 feet from the center of the panel). At approximately 60 feet from your house, the subsidence would be less than an one-eighth of an inch. We noted that under this scenario that the railroad would have dropped 9.11 feet as it is located at the center of the subsidence curve. we found no evidence in the field indicating that the railroad tracks had subsided. I hope that this information will be helpful in evaluating the findings recently sent to you. This subsidence model is used throughout the Nation, and field measurements have been used to validate its accuracy in predicting subsidence. Companies can vary their extraction ratios depending upcn the strength of the mine ceiling, the strength of the coal in the pillars, and the floor bearing strength. Generally companies will decrease their extraction ratio beneath or adjacent to structures or other sensitive surface features. Soft floor conditions can be a reason to decrease the ratio. If you have any questions concerning this information please contact me at 303-672-5501. Sincerely, Charles E. Acting Regi Western Reg Center Director Coordinating Enclosures