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Bureau of Land Management Environmental Assessment <br /> Royal Gorge Field Office DOI-BLM-CO-F020-2020-0036 EA <br /> After coordination with the operator, the proposed mining method would replicate what is <br /> presently being implemented at the active quarry (Appendix B, Exhibit C), with minor changes <br /> to the highwall and bench design, site preparation schedule (e.g., stripping, sloping, contouring, <br /> etc.) and frequency of mining/processing equipment use. Section 2.1.3 summarizes the current <br /> and proposed project design features that would be implemented onsite. <br /> Reserves and Mine Life <br /> Due to variable overburden thicknesses throughout the mine extent, a maximum total mining <br /> depth would be projected at 200 feet. The most recent working floor has a bottom elevation of <br /> 8,020 feet. As a result of recent exploration drilling,the operator has projected a max bottom <br /> deposit elevation of 7,935 feet, for a total elevation change of 85 feet for the overall mine <br /> expansion proposal. Mining progression would gradually continue until either the mineral <br /> material reserves are exhausted or are no longer economically viable. With a maximum deposit <br /> thickness of 120 feet and total proposed disturbance of 10.75 acres (468,270 ft), approximately <br /> 3,823,596.18 tons (1,911,798.09 yd3) of federal mineral reserves would be available for <br /> production within the proposed expansion boundary. As the maximum extent of the obsidian <br /> deposit is unknown,the reserves in the far northern region proposed in the potential reserves' <br /> boundary described in section 3.2 (Figure 7)not included in the proposed expansion boundary <br /> calculations. The operator predicts that the quarry could continue producing material for at least <br /> 25 years; however, the extent of the mine life would strongly depend upon the future demand <br /> and viability of the obsidian material and maximum extent of the deposit. <br /> Site Preparation—Stripping Topsoil and Overburden <br /> Prior to mining, site preparation would consist of stripping all topsoil and overburden from the <br /> maximum highwall/bench configuration extent(approximately 15 acres; Figure 3). <br /> Approximately, 5,000 yd3 of stripped topsoil would be stockpiled in a designated area with a 2:1 <br /> slope and revegetated with a native seed mixture for stabilization. Sediment controls(e.g., silt <br /> fences)would be installed along the base of the stockpile to control erosion and preserve the <br /> material. Most of the topsoil material would be stored for use in final reclamation. During final <br /> reclamation, 3 to 6 inches of topsoil would be spread along all disturbed areas such as <br /> overburden cells, overburden slopes above quarry highwalls, earthen stormwater control <br /> structures, road cuts and fills and pad outslopes. <br /> An estimated 20,000 yd3 of overburden would then be stripped from the area and sloped back to <br /> 2:1 above the margins of the quarry highwall. Initially, stripped overburden would be used to <br /> construct stormwater control features and expand the working floor near the base of the <br /> highwall. Excess overburden, approximately 10,000 yd3, would be permanently stored north of <br /> the active quarry (Figure 3) with slopes no greater than 2:1 and revegetated with a native seed <br /> mixture. Of the total production volume, an estimation of 15%overburden and 85%product <br /> would be mined. <br /> 8 <br />