2008-02-22_APPLICATION CORRESPONDENCE - C2008086 (39)

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CHAPTERFOUR Environmental Consequences and Mitigation a stable and productive vegetation community adequate in quality and quantity to support the planned postmining land uses (wildlife habitat and rangeland). There would be an increase in the near-surface bulk density of soil resources after reclamation. As a result, the average soil infiltration rates would generally decrease, which would increase the potential for runoff and soil erosion. Topographic moderation following reclamation would potentially decrease runoff, which would tend to offset the effects of decreased soil infiltration capacity. The change in soil infiltration rates would not be permanent because revegetation and natural weathering action would form a new soil structure in the reclaimed soils, and infiltration rates would gradually return to premining levels. The reclaimed landscape would contain stable landforms and drainage systems that would support the postmining and construction land uses. Mine and Facilities The mine facility site will impact the following soil map units: • Killpack-Badlands-Persayo complex; 3 to 12 percent slopes; saline • Mesa-Avalon complex; 3 to 12 percent slopes • Tolman-Rock outcrop-Chugcreek complex; 3 to 12 percent slopes; very stony • Persayo silty clay loam; 3 to 25 percent slopes • Moffat-Kompace complex; 6 to 35 percent slopes • Chipeta silty clay loam; 3 to 30 percent slopes • Leebenchwarm-Avalon complex; 3 to 12 percent slopes The proposed mine facility is located on soil map units that have high erosive potentials (Persayo, Chipeta, and Badland); therefore, erosion and sedimentation should be mitigated during construction of the mine facility site. These soil map units formed in residuum from alkaline marine shales containing gypsum, which is corrosive to concrete and is known to lower fertility and plant water availability. Moreover, both the Persayo and Chipeta soil series have high shrink-swell capacities, which can cause structural damage to structures and foundations. When disturbing the natural land surface in these areas of shale and other soft sedimentary material, it is advised to avoid constructing in locations generally prone to landslides, including steep slopes or the base of slopes with noticeable mass movement. These attributes may cause limitations during construction and overall maintenance of the mine facility site. Railroad The proposed construction of the rail spur will impact the following soil map units: • Killpack-Persayo complex; 3 to 25 percent slopes • Killpack-Badlands-Persayo complex; 3 to 12 percent slopes; saline • Leebench warm-Avalon complex; 3 to 12 percent slopes • Persayo silty clay loam; 3 to 25 percent slopes • Killpack silty clay loam; 0 to 2 percent slopes 4-77 DBMS 632