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

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CHAPTERFOUR Environmental Consequences and Mitigation North of the Highline Canal, the Killpack-Persayo and Killpack-Badlands-Persayo complexes dominate the rail spur alignment. South of the canal, the Persayo silty clay loams dominate the alignment and are primarily used as agricultural parcels. These soil map units that have high erosive potentials; 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. The Persayo soil series has high shrink-swell capacities, which can cause structural damage to structures and foundations. Moreover, the Killpack soil series formed in alluvium and residuum from saline marine shale. Saline inhibits or eliminates re-vegetation potential in the affected area because of increased soluble salt concentrations in the root zone of the soil (MRCS 2004). Selenium also occurs naturally and is present in these sedimentary formations. This element is required in trace amounts for human and animal health, but it can have adverse health problems for livestock, wildlife, and humans when ingested in higher-than-required concentrations. The high selenium content in the region is known to have adversely affected fish and avian populations, and the salinity has impacted agricultural lands, water delivery facilities, and water quality (USGS 2007). Transmission Line North of the Highline Canal, the transmission line will impact the following dominant soil map units: • Killpack-Persayo complex; 3 to 25 percent slopes • Persayo-Blackstone complex; 6 to 45 percent slopes • Badlands-Deaver-Chipeta complex; 25 to 99 percent slopes; extremely stony • Mack-Avalon complex; 3 to 12 percent slopes • Killpack-Neiberger complex; 3 to 25 percent slopes These dominant map units are moderately to very deep, well-drained soils that formed in slope alluvium and alluvium derived from sandstone and shale on sideslopes and toeslopes of rolling shale hills. Once again, these soils have high erosive potentials, high shrink-swell capacities, and high selenium, saline, and gypsum levels. South of the Highline Canal, the transmission line will impact the following dominant soil map units: • Sagers silty clay loam; 0 to 2 percent slopes • Killpack silty clay loam; 0 to 2 percent slopes • Ustifluvents; 0 to 2 percent slopes The Sagers and Killpack silty clay loam map units are moderately to very deep, well-drained soils that formed in alluvium and residuum from saline marine shales. These soils are on basin and valley floor remnants, alluvial fans, and stream terraces. Ustifluvents are moderately well- drained soils found on flood plains formed in alluvium derived from sandstone and shale. The soils that compose the alignment south of the canal are primarily used for agricultural production and may be irrigated. Some of these soils are considered prime farmland if irrigated, and impacts on them should be minimized. 4-78 DBMS 633