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• Extension of Rock Subdrains <br />In order to provide for effective drainage from the stockpile foundation, <br />the previous mine operator, Dorchester Coal Company, constructed a rock <br />subdrain extending under the existing refuse pile. As a result of <br />concerns relative to the importance of effective drainage on refuse pile <br />stability and the potential for blockage of the primary subdrain if <br />significant subsidence were to occur in the refuse pile area, the MLRD <br />specified and Dorchester designed and constructed a secondary subdrain as <br />the existing stockpile advanced to the west. <br />Similar foundation drainage considerations are applicable for the proposed <br />refuse pile expansion. Accordingly, EFCI will extend the existing primary <br />and secondary Subdrains in sequence with refuse pile advance. Rock <br />subdrain specifications and construction will be consistent with the <br />design recommendations presented in Appendix 1, Geotechnical Report, which <br />• were also utilized in constructing the existing rock Subdrains. <br />The rock subdrain extensions will be established with a minimum gradient <br />of two (2) percent, subdrain material will consist of durable rock fills, <br />and drain material will be wrapped with Typar 3401 filter cloth or <br />equivalent to prevent clogging. The locations of the existing rock <br />Subdrains, and the proposed primary and secondary subdrain extensions are <br />shown on the Coal Refuse Pile Expansion Map (Map TR07-1). <br />Coal Refuse Placement <br />Following establishment of the drainage collection ditches, preparation <br />of the foundation area, and progressive construction of the subdrain <br />extensions, EFCI will proceed with coal refuse placement in expansion <br />areas. Coarse and fine refuse materials will be hauled from the on-site <br />preparation plant to the coal refuse pile and dumped. Refuse materials <br />will be spread by a tracked dozer in horizontal lifts of no greater than <br />. two (2) feet. <br />8R Revised - February, 1990 <br />