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Potential causes of Suosidence of the Solitario Ranch House Page 3 <br />operations. Water tables can be raised in a relative sense, if water tables stay at the <br />same elevation and subsidence occurs, then the water table appears to have raised <br />relative to the surface. <br />Basin Resources has stated that their activities could affect the water table. <br />Subsidence Due to Underground Mining <br />Subsidence could have been caused by underground mining. Subsidence over room <br />and pillar coal mining systems does occur, even at limited 50 % extraction. Over <br />time, the mine roof may fail, the pillars may fail, or the mine floor may fail. Failure <br />is often accelerated by water in the mine, affecting the stability of the rocks, and <br />failure can also occur when the floors are soft. Both of these conditions are <br />apparently present in 1 North, according to the statements that were made in the <br />deposition of Ron K. Thompson, 12/10/93. <br />The exact location of mining activities with respect to the house is only estimated <br />from maps that have a scale of 1 in. = 500 ft. (See Map 1) There is no evidence that <br />the location of the house was surveyed. There are no measurements to establish a <br />base line of data for subsidence before mining commenced. <br />The workings in 1 North are wide enough so that the effects of subsidence could be <br />reflected at the surface. The usual rule of thumb is that subsidence can occur if the <br />width is I.4 times the depth. The depth is calculated to be 445 ft, as stated in a <br />letter from Dan Hernandez of the Colorado division of Minerals and Geology to <br />Michael A. Ossola Las Animas County Planning and Land Use Office, dated 8/12/93. <br />The width is scaled to be 646 ft. (445 ft. X 1.4 =623 ftJ <br />The angle of draw is an empirical measurement that is site specific, Basin <br />Resources does not report a measured angle of draw and 35 degrees is a number <br />often used in the literature as basis for estimate. It is also the number proposed by <br />Jim Pendelton of the Colorado Division of Minerals and Geology in a Memo dated <br />January 19, 1994, concerning subsidence due to mining at the Golden Eagle Mine. <br />It can be shallower, that is, affecting a larger area, and some investigators report <br />that it can be shallower in near-surface sediments. There are also reports of <br />evidence of slight elevation of the surface adjacent to the subsided zone beyond the <br />intersection of the surface with the angle of draw. <br />Subsidence affects the land surface in the form of tension in the surface at the <br />interface between it and the angle of draw, and this stretching zone can be the area <br />of the most damage in structures, especially in the upper stories. <br />~lhere are structural lineaments or zones, in the rock in the area, these can be <br />determined from the aerial photographs and topographic maps. One of these zones <br />is aligned with the front (east) side of the house. (Map 1) These zones could also <br />change the extent of rock failure during subsidence. They could also transmit <br />PIONEER ENGINEERING <br />