1987-12-01_PERMIT FILE - C1981017 (185)

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Chapter IV topography. The potential aquifers have limited surface exposure. Recharge effectiveness is further reduced because the recharge areas are well channeled to the east and effectively sealed from above by shales and mudstones in the series. Subsidence would not be expected to change the limited flow of ground water presently flowing into the mines which is pumped to the surface, or which may enter the sandstone occurring below the lower coal seam. There will be no diminution of aquifer recharge caused by subsidence. (See Collins' study at Appendix IV -F -4). 3. Determination Statement of the Effects of Subsidence, if it Did Occur, on Material Damage or Diminution of Reasonably Forseeable Use of Structures or Renewable Resource Lands. Mid - Continent believes that subsidence resulting from its mining operations in Coal Basin over the next five year period is highly unlikely. Also, that if subsidence does occur, based on a worst case hypothesis, there will be no material damage or diminution of reasonably foreseeable use of structues or renewable resource lands. Our field observations are that the nature of overlying strata is such that rock strengths are adequate to withstand the gravitational stresses over great widths and tha the voids created by the subsiding material are rapidly filled with overburden material which increases in volume with sufficient strength to choke off subsidence before the surface is breached. An extensive area of B Bed, nearly six miles along strike and one mile downdip, has been mined 400 to 500 feet vertically below the Middle Bed. Total amount of the cover above the B Bed should have generated subsidence effects in the Middle Bed above the areas mined, but no subsidence has been detected therein. There is no conceivable possibility that the Middle Bed area has subsided en toto because no indications of such occurrence appear in the main drifts, development entries, or on the ground surface in transition areas. The summary of opinion is that subsidence will not reach the ground surface over the federal leased areas. This opinion is derived from the historic factors cited and a comparison of probable subsidence as illustrated: Depth /Feet Subsidence Coal Bed Ratio Thickness Feet 2200 0.55 24 2800 0.55 24 32 Maximum Percent of Subsidence Depth Feet 13.2 0.6 13.2 0.47 The normal bulking factor resulting from excavated rock is 35 to 50 percent before compaction or settling. Therefore, a void of 24 feet would be filled and the supplying