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Response: <br /> Based on observations at the site following the September 2013 flooding in South <br /> St. Wain Creek, a significant storm is required to impact the proposed scour berm. <br /> The latest available FEMA mapping shows elevations of the Base Flood (100-year <br /> flood or 1% annual chance) ranging across the site from El. 5541 to El. 5505 <br /> (NA VD 1988). These elevations are below the level of channel scour that was <br /> observed at the site adjacent to the existing pit and waste piles. Technical <br /> Revision No. 2 is revised to state that the scour protection will be designed for a <br /> minimum 100 year flood event and that the size of riprap will be determined during <br /> final design. The riprap gradation used for the scour berm in the preliminary <br /> design assumed a D50 between 36 and 48 inches. <br /> 22. The Reclamation Plan calls for reducing the existing highwall to 1.5H:1V <br /> through drilling and blasting. In addition, the Reclamation Plan calls for backfilling <br /> portions of the reduced slope to 2HAV, while other areas of the reduced slope will <br /> remain at 1.51-1:1V and will receive a two foot cover of riprap talus. Please explain <br /> why 4.8 acres of the site will not be backfilled to 2HAV. <br /> Response: <br /> The mining operations to date have not produced the necessary quantities of <br /> overburden sedimentary rock required to cover the pit highwalls at the 3H:1 V fill <br /> slopes shown in the current Reclamation Plan. This Technical Revision No. 2 <br /> shows final slopes that: <br /> • Provide for stability of all reclaimed slopes, highwalls, waste piles, and <br /> embankments <br /> • Provide stable 2H:1 V fill slopes that buttress and stabilize the pit highwalls <br /> • Provide stable 1.5H.1 V cut slopes that stabilize the overburden sedimentary <br /> rock <br /> • Result in a balanced cut and fill at the site <br /> The 1.5H:1 V cut slopes in the overburden sedimentary rock is separate and above <br /> the top elevation of the 2H:1 V fill slopes placed against the pit high wall. These cut <br /> slopes comprise the 4.8 acres that are not backfilled to 2H:IV. The Engineering <br /> Stability Analysis shows that these cut slopes are stable without backfill, similar to <br /> the natural slopes in sedimentary rock adjacent to the site. <br /> 23. The Reclamation Plan Map which depicts the final configuration of the high wall <br /> does not conform the requirement of Rule 6.2.1(2). The Reclamation Plan Map <br /> 11 <br /> hdrinc.com <br /> 1670 Broadway, Suite 3400, Denver, CO 80202-4824 <br /> (303)764-1520 <br />