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pipe. The pond area has sufficient capacity to store runoff from the probable maximum precipitation <br />(PMP) event (5 inch rainfall) without overtopping its embankments. <br />4.0 RPEE Waste Rock Pile Permit Desiqn <br />The RPEE waste rock pile design is presented on the permit drawings provided in Appendix D. The <br />layout of the waste rock pile is based on geotechnical analysis and design provided in Section 2. Key <br />components of the waste rock pile design are presented below. RPEE coal refuse storage capacity is <br />shown on a figure in Appendix G. <br />4.1 Stripping <br />Vegetation will be removed and available vegetative soil (or topsoil) will be stripped from the waste <br />rock pile footprint prior to preparing the site for placement of coal refuse materials and constructing <br />underdrainage and surface water drainage controls. Vegetation that can be chipped in place will be <br />mixed with the vegetative soil to enhance organic content. Topsoil is estimated to be approximately <br />24 inches thick on average in the footprint of the waste rock pile. Topsoil has been found to be <br />thicker near the thalweg of the gulch and thinner towards the east and west edges of the waste rock <br />pile footprint. <br />Vegetative soil will be placed in designated stockpiles until needed for contemporaneous reclamation <br />as the face of the waste rock pile reaches design grade. After vegetation and vegetative soil has been <br />stripped, the remaining foundation surface will be benched to prevent the development of a shear <br />plane between colluvium and refuse materials. Interim stockpiles may also be constructed above <br />(south of) the newly prepared waste rock pile site until the soils are used for contemporaneous <br />reclamation or moved to another approved stockpile site. <br />4.2 Buttress <br />A rock buttress stabilizes the toe of the RPEE waste rock pile as required by the Rules. Prior to <br />buttress construction, the buttress area was stripped of soils and colluvium down to bedrock. A <br />keyway was cut into bedrock near the toe of the buttress. The buttress is constructed of rock with <br />colluvium on the upstream, as shown on permit drawing C-04 (Appendix D). The buttress has a slope <br />of approximately 1.911:1 V on its north face (away from the waste rock pile) and a slope of <br />approximately 1H:1V on the south face, against which refuse has been placed. <br />19 <br />P:\Mpls\06 CO\26\06261003 MCC Refuse Pile Site Review & Permit\WorkFiles\Permit Application\2014 Revision\Exhibit 82 2014-05- <br />29.docx <br />