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to the coal refuse structure would occur if the sub-entries <br />• under the north area pile would be extracted prior to the main <br />entries under the remaining portion of the pile. <br />If sub-mains will be extracted prior to the main entries, an <br />additional rock drain, similar in design to the existing drain, <br />would need to be installed at a location just inside the limits <br />of the advancing face of the sub-entry. The rock drain should be <br />installed along the entire limits of the refuse pile and should <br />extend downstream of the refuse pile toe. The installation of <br />the rock drain will allow seepage to be carried away from the <br />refuse pile area and thereby, maintain the reported factor of <br />safety calculated for the refuse pile. <br />As discussed in Section 2.0, the only other mitigation <br />measures performed will be that of minor regrading of the refuse <br />• pile to prevent ponding of water and regrading to fill in surface <br />cracks produced on the top portion of the refuse pile. <br />3.4 Power Lines <br />The resultant extensions or constrictions of the power lines <br />can be mitigated by measures conducted prior to coal extraction <br />and following subsidence. <br />Measures conducted prior to coal extraction will consist of <br />reducing tension within the lines to allow for the expected <br />tension/extension strains to be dissipated and allow for <br />longation of the lines within the expected affected areas. <br />Measures conducted following subsidence consist of shortening <br />lines or raising power poles where subsidence has reduced <br />electrical clearances. Based on conversation with officials from <br />• Southern Colorado Power District, these measures can be <br />27 <br />