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May Day Idaho Mine Complex- 112(d)Permit Anrendntent <br /> April 17,2017 <br /> Tile historical tailings deposited on the floodplain are of unknown date or origin. These were <br /> characterized by a uniform sandy loam texture, and while this material supported abundant <br /> riparian vegetation, there was minimal soil development (Plate 5). A wetland mitigation project <br /> was undertaken in 2008 within this material and did not show any soil development (Plate 5). <br /> 2.5 Mine Rock <br /> Mine rock was present on the outslope of benches at the May Day No. 1, May Day No. 2, and <br /> Lamb Operational Area. Mine rock was present above the Idaho Operational Area. These areas <br /> were characterized by coarse,angular mine rock of gravel to cobble size with a matrix of fine <br /> grained material on slopes of 30-35°. There was no evidence of soil development, but <br /> regeneration was observed on these slopes (Plate 6). <br /> 3.0 Topsoil Availability <br /> "Topsoil"describes soil that should be salvaged before project ground disturbance. It is suitable <br /> for establishment and maintenance of plant growth, and is not necessarily the A, E, or B horizon, <br /> but may be any or a combination of those horizons. For a soil horizon to be considered topsoil, it <br /> had to meet the topsoil suitability criteria presented below: <br /> • Less than 15%rock fragments. <br /> • More than 1.0%organic matter. Soil color was used as the indicator of percent organic <br /> matter. The horizon needed to have a 10YR 4/3, moist, or darker color to meet the <br /> organic matter criterion. <br /> • Loamy textures—silty clay loam, silt loam,loam, sandy clay loam, sandy loam, or clay <br /> loam <br /> • A pH between 6.5 and 7.8. <br /> • Electrical conductivity(EC) of less the 8 decisieniens/m(dShn) - estimated based on the <br /> presence of visible salts; if visible salts were present the EC was considered greater than <br /> 8 dS/m. <br /> • A sodium adsorption ratio (SAR)of less than 13 —estimated based on the presence of <br /> columnar structure in the Bt horizon; if columnar structure was present the SAR was <br /> considered greater than 13. <br /> The main limiting factor for topsoil recovery is the presence of rock fragments. Soil salvaging <br /> and stockpiling will not be undertaken for the following reasons: <br /> • the collection of topsoil on the steep slopes will be difficult; <br /> • the separation of topsoil from the rock fragments would greatly reduce the volume of <br /> topsoil to be salvaged; <br /> • the limited area to store stockpiled topsoil; and <br /> • the fact that natural regeneration on disturbed areas indicates that topsoil is not required <br /> for reclamation. <br /> May Day Idaho Mine Complex 112(d)Permit Application <br /> Revised April 10,2017 <br /> 3 <br />