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Mike Boulay <br />-39- October 16, 2012 <br />114. Regarding the potential for surface cracking, permit text narrative on page 2.05- <br />71 uses the term "retreat line" as a reference for identifying surface cracking <br />develop "parallel" to this line. Please modify permit text narrative, explain the <br />orientation of the retreat line, and /or be more specific on the expected <br />orientation of surface cracks. <br />MCM: Retreat mining is the last phase of room and pillar mining. In room and pillar <br />mining a mining machine called as continuous miner bores a network of <br />chambers or "rooms" into a coal seam, leaving at the back an unexcavated pillar <br />of coal in every room to support the roof of the mine. Room and pillar mining <br />proceeds inner, away from the entrance of the mine. When the coal seam goes <br />out or the mine's property line is reached, retreat mining is a method that <br />recovers the supporting coal pillars, working from the back of the mine through <br />the entrance, thus the word "retreat." Text has been added to page 2.05 -70 for <br />clarification. <br />115. On page 2.05 -71, permit text narrative states "cracks could be a few inches wide <br />and long enough to go across the entire roadway." How was this conclusion <br />reached? What study or information was used to conclude that surface <br />cracking will be limited to a few inches in width? <br />MCM: The conclusion was reached because the area to be mined is under deep cover, <br />and 30 years of experience observing subsidence phenomena at other western <br />Colorado mines. <br />116. Subsidence cracking of ephemeral drainages could interfere with runoff from <br />over 2000 acres of land directly and indirectly. What monitoring and /or <br />mitigation measures are proposed for potential impacts to runoff and to <br />downstream water users? <br />MCM: As stated on page 2.05 -71, which according to Rule 2.05.6(6)(b)(i)(C) is a worst <br />possible consequence, "Flow through the drainages could temporarily be <br />affected by a subsidence crack across a stream channel, however, the crack <br />would be expected to heal fairly quickly so the surface drainage pattern would be <br />naturally restored ". MCM contends that the ephemeral drainages in the area are <br />too steep to cause a long term disruption to the drainage pattern, and due to the <br />fact the drainages are ephemeral, long term disruption to the drainage pattern is <br />not likely. As shown on Figure 2.1 -8, the majority of the proposed mine plan will <br />have cover in excess of 500 feet, with a large portion of the mine plan under <br />1000+ feet of cover. Mining under higher cover will produce less surface <br />subsidence, thus, less cracking and potential interruption to ephemeral <br />drainages. No mitigation is proposed. <br />