2017-09-28_REVISION - M1981185 (145)

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