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indicates that no evidence exists of new subsidence <br />• and that the Huntington Ditch shows no evidence of <br />being affected by underground mining. National <br />King Coal continues to monitor for subsidence <br />effects on a quarterly basis. Some monitoring is <br />also performed periodically by the various <br />regulating agencies (OSM and CDMG). <br />The above evidence suggests that subsidence could <br />occur due to extraction of the 4.5 to 6-foot coal <br />seam and pillars on retreat in the proposed <br />modification area. Although a maximum subsidence <br />of 6 feet could occur, the most likely showing on <br />the surface would be tension cracks such as the <br />ones identified on Federal lease P-058300. In <br />addition, as a result of the requirement for the <br />quarterly monitoring of the mine for subsidence and <br />the greater thickness of overburden, it is not <br />anticipated that subsidence will be evidenced to <br />the degree that was noted on Federal lease <br />P-058300. <br />Subsidence fractures could allow the escape of <br />methane gas to the surface and could increase the <br />hazard of underground and surface fires. Although <br />this is not likely due to the low liberation of <br />methane of the Menefee coal (less than 1~), the <br />• potential of causing surface impacts is present. <br />Colorado Division of Minerals and Geology (DMG) <br />rules 2.05.6 and 4.20 require that "underground <br />mining activities shall be planned and conducted so <br />as to prevent subsidence from causing material <br />damage to the surface...". Material damage is <br />defined in Rule 2.05.6 with respect to subsidence <br />as changes which prevent restoration of affected <br />structures and with respect to renewable resource <br />lands; changes which disrupt an aquifer, or a <br />recharge area to an aquifer, which serves as a <br />beneficial use of water; or changes which prevent <br />restoration of productivity for agricultural lands. <br />Implementation of these regulations will minimize <br />the impacts of subsidence. <br />4. Vegetation <br />Direct Impacts- Some minimal impacts to vegetation <br />would result if subsidence occurs. <br />Indirect Impacts- No impacts have been identified. <br />Cumulative Impacts- No impacts have been <br />. identified. <br />15 <br />