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