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NON-CRITICAL ELEMENTS <br />1. Soils <br />Since only minimal active surface disturbance is proposed, soil impacts from these impacts would <br />be minimal. Subsidence could occur, which could result in some low-volume, localized soil <br />erosion. At the time that support pillars are removed, a cumulative impact from subsidence could <br />occur throughout the mined area. However, in light of the requirement in State regulations to conduct <br />operations in such a manner as to control or prevent effects of subsidence, this is not expected to be a <br />major concern. <br />2. Geology and Mineral Resources <br />Subsidence fractures could impact topography and surface features in the area of the proposed lease. <br />The DMG rules require that "underground mining activities shall be planned and conducted so as to <br />prevent subsidence from causing material damage to the surface..." Material damage is defined with <br />respect to subsidence as changes which prevent restoration of affected structures and with respect to <br />renewable resource lands; changes which disrupt an aquifer, or a recharge area to an aquifer, which <br />serves as a beneficial use of water; or changes which prevent restoration of productivity for <br />agricultural lands. <br />In addition, National King Coal's permits to mine coal from Colorado DMG and OSM require that <br />the company monitor subsidence on a quarterly basis. Some monitoring is also preformed <br />periodically by the various regulating agencies (OSM and DMG) during inspections. <br />Evidence of subsidence fractures following pillar extraction in 1979 has been noted on National <br />King Coal's Federal lease P-058300 in an area approximately 300 feet north of the lease boundary <br />and on the east limb of the lease above the western edge of pillars that were extracted. Subsidence <br />fractures have also been observed in the 100 -acre portion of the existing mine located on Ute <br />Mountain Ute owned land. Specifically, monitoring has found that some subsidence fractures <br />appeared about 6 months after pillar extraction began. Cracks ran for a distance of about 200 feet <br />where overburden depths ranged from 100 feet (drainage ways) up to 300 feet (ridge tops) and <br />tended to follow the contour of the surface topography. They opened as much as 6 to 12 inches wide <br />and 9 feet deep with most evident cracks being on the side slopes. Frost -heaving and sediment <br />deposition reduced crack size to 1 to 2 inches within 12 months after they first appeared. There was <br />no apparent change in ground elevation or land use. <br />Subsidence could also occur during the extraction of 4.5 to 7 -foot coal seam pillars on the retreat in <br />the proposed 1,304.51 -acre lease area. While a maximum subsidence of 7 feet could occur, the most <br />likely showing on the surface would be tension cracks such as the ones discussed above. The greater <br />thickness of overburden in this area (i.e., 300 to 400 feet), however, suggests that subsidence will not <br />be as evident as it has been in those areas. <br />Subsidence fractures could also allow the escape of methane gas to the surface and could increase the <br />hazard of underground and surface fires, although this is not likely due to low liberation of methane <br />19 <br />