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P <br />i <br />l <br />f S <br />id <br />~ <br />b <br />• <br />otent <br />a <br />rsu <br />u <br />o <br />s <br />ence of the Solitario Ranch House <br />Page 3 <br /> <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 />e _ ,p,,,,~p" ~ Basin Resources has stated that their activities could affect the water table. <br />1 <br />f Subsidence Due to Unde <br />rground Mining <br />Subsidence could have been caused by underground mining. Subsidence over room <br />and pillar teal 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 p- <br />apparently present in 1 North, according to the etatementa that were made in the +~DN~I• ~,,~ <br />- deposition of Raa K Thompson, 12/10/93. <br />- ~n <br />The exact location of mining activities with respect to the house is only estimated <br />~ <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 ao 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 1.4 times the depth. The depth ie calculated to be 445 ft, ae stated in a <br />letter from Dan Hernandez of the Colorado division of Minerals and Geology to <br />Michael A. Oseola Las Animas County Planning and Land Uee Office, dated 6/12/93. <br />The width is scaled to be 646 ft. (445 ft. X 1.4 =623 ft.) <br />The angle of draw is an empirira] measurement that is site specific, Basin ~ QZ <br />-Resources~doesmot+reporta+neasuredangle.ofdraw.and 35 degrees is a number <br />~ <br />ofteu~used4n~the~iteratureae~basis#oreatimate.lt~salso.the~oumber~proposetl~ ~ ~ <br />dim'Pendettoaroftlfa'C'eltlradai?'ivisionof~iKineiBlsandreology3n.a Memod, <br />danuaryd9,d99Q, concerning subsidence due to mining at the Golden Eagle Mine. ,I?P i _ 19 _q~ <br />It can be shallower, that ie, affecting a larger area, and some investigators report <br />that it can be shallower in near-surface sediments. There are also reports of '1'^°'W`~' <br />evidence of slight elevation of the surface adjacent to the subsided zone beyond the <br />_~.. •. ;d;. intereection of the surface with the angle of draw. <br />- Subsidence ati'ects tiie land surface in the form otteneion 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 /> ~ <br />''"~ <br />"^~~ <br />There are structural lineaments or zones, in the rock in the area, these can be ' <br />' <br />determined from the aerial photographs and topographic maps. One of these zones <br />is aligned with the front (east) aide 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 />