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<br />i <br />Mr, and Mrs. Tatum <br />March 16, 1995 <br />Page 4 <br />understand that coal is being extracted by long wall mining methods in the area northeast of <br />the residence, on the north side of the Purgatoire River Valley. Previously, mining has taking <br />place beneath the hillside south of the valley, south of the residence. Mining in that area was <br />by room and pillar methods. <br />We understand that the mining operators intended to connect the two portions of the mine <br />by mining a zone extending from the south that would have passed directly beneath the <br />residence. This 625 feet wide room and pillar zone was extending northward towards the <br />residence when the mining effort was abandoned. We understand the mine encountered wet <br />ground conditions and a weak floor. We understand the area has since been flooded and <br />sealed off. Based on maps provided to us by Mr. Gerity, it appears that the mining from a <br />depth of about 450 feet came within 200 to 300 feet of the residence. <br />EFFECTS OF MINING <br />Because of loss of ground, subsidence can occur over areas of mining. There are differences <br />between the subsidence potential over room and pillar and long wall mined areas. In long wall <br />mining, coal is completely extracted within a large area known as a panel. As a result, <br />subsidence at the surface may approach the thickness of the extraction zone beneath. With <br />room and pillar mining, unless the pillars are removed, ordinarily surface subsidence should not <br />be as great as with long wall mining. We understand there was an effort to control or <br />minimize surface disruption as the mining proceeded northward, as only about 40°~ of the coal <br />was extracted. Typically, this would minimize surface disruption. However, according to Mr. <br />Gerity, the soft floor of the mine may have resulted in pillar failure in the area of the mine <br />nearest the residence. If that occurred, then surface disruption could be more analogous to <br />long wall mining than room and pillar mining. <br />Mining engineers and rock mechanic experts have attempted to develop methods to predict <br />surface subsidence over coal mining. A concept has been developed called the "angle of <br />draw", within which the effects of mining might be felt. The angle of draw is a fairly simple <br />representation of possible earth movements and consists of a plane extended upward from the <br />outer toe of the mine towards the ground surface. The angle of this plane from the vertical <br />is called the angle of draw. Depending on the geology and other conditions, angles of draw <br />would typically be in the range of 25 to 35 degrees. It is our understanding that the Tatum <br />residence may be located very close to the zone where the angle of draw would encounter the <br />ground surface. <br />POSSIBLE CAUSES OF RESIDENCE DAMAGE <br />In order to evaluate likely causes of the damage to the residence, a number of possible <br />scenarios have been suggested or may exist. We present each of these with our comments. <br />f:~projsct~~250180 7 .hr <br />