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BACKGROUND <br />• In conjunction with ongoing underground coal mining operations, Oxbow Mining LLC <br />(OMLLC) generates limited quantities of coal refuse and non-coal processing waste <br />material. In order to address current and future operational requirements for disposal of <br />coal refuse and non-coal processing waste material in a safe and environmentally <br />compatible manner, OMLLC needs to permit and develop a new coal refuse disposal <br />facility. <br />OMLLC has completed designs for the new coal refuse facility, designated as the II West <br />Coal Refuse Facility, located in the second ephemeral drainage to the west of the existing <br />West Valley Coal Refuse Facility, as shown on the Genera] Facilities Map, (Map 2.05- <br />Ml (Sheet 5 of 5)). The proposed coal refuse disposal facility will be designed, operated, <br />and reclaimed in essentially the same manner as the present West Valley Coal Refuse <br />Facility. Site investigations for the proposed coal refuse facility included geologic <br />mapping, soils borings, a geophysical survey to determine depth to bedrock, and site <br />reconnaissance for any springs or seeps. No springs, seeps, or other ground water <br />sources were found in the refuse pile foundation area. Geologic and foundation <br />conditions are addressed in the II West Coa] Refuse Facility Design Report (Design <br />Report) prepared by Environmental Strategies Corporation (ESC). The ESC Design <br />Report, included in Exhibit 2.05-E4, also includes designs and geotechnical stability <br />analyses for the proposed facility. <br />• The refuse facility design reflects interception and diversion of al] potential runon by <br />designed diversion ditches, and collection and routing of al] runoff from the refuse <br />facility to perimeter collection ditches. The ESC design assumed effective drainage of <br />any seepage or infiltration through the refuse pile by means of a designed rock <br />underdrain, as required by the applicable regulatory provisions of Rule 4.09.2(2). <br />Because all surface drainage is handled by designed diversion and collection ditches and <br />no ground water sources were found in the refuse facility foundation area, underdrain <br />design is based on potential maximum infiltration of precipitation directly incident on the <br />refuse facility area. This design report addresses design and construction of the required <br />rock underdrain, consistent with the applicable regulatory provisions and accepted <br />engineering design practices. <br />UNDERDRAIN DESIGN <br />The required rock underdrain is sized to safely pass the maximum flows resulting from <br />infiltration through the refuse pile, using a conservative (high) permeability figure as the <br />limiting factor to determine maximum infiltration rates and corresponding underdrain <br />flows. Design calculations assume that the drain will be constructed of naturally- <br />occurring durable sandstone rocks and cobbles recovered during foundation preparation <br />activities for the coal refuse pile. The following calculations address rock underdrain <br />sizing requirements. <br />• <br />