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Evaluation of Potential Subsidence Impacts of Longwall Mining in the Spruce Stomp Lease Area <br />to Aquatic Life and Water Supply <br />The land in the area is primarily used for grazing cattle and subsurface coal mining. Additional <br />uses include water supply for downgradient farms and municipalities, recreation, hunting, fishing <br />and limited timber harvest. <br />4.1.3 Geology /Geologic Features <br />The underlying geology of the West Fork Terror Creek watershed consists of primarily <br />sedimentary deposits of the Tertiary Wasatch Formation, Upper Cretaceous Mesaverde <br />Formation and Quaternary deposits (U.S. Department of Agriculture, 2000). The Mesaverde <br />Formation is the primary coal- bearing formation in this area. The Tertiary Wasatch Formation <br />was transported and relocated following the Mesaverde Formation and consists of sandstone, <br />shales and conglomerates. Quaternary deposits (alluvium, colluvium and landslides) consist of <br />soil and rocks which have been deposited as a result of mass wasting processes. The West Fork <br />Terror Creek watershed contains primarily historic geologic hazards, but during high periods of <br />rain, landslides on steep slopes may occur (U.S. Department of Agriculture, 2000, U.S. <br />Department of Interior, 2005). Regional and site specific surficial geologic mapping in the <br />Potential Project area are shown on Figures 4 and 5, respectively. <br />Landslide activity was observed along one reach of West Fork Terror Creek within the Potential <br />Project area during an April 2012 site visit. Signs of earth movement included trees growing at <br />irregular angles, exposed bare earth at small head scarps, downed trees and areas with trees of a <br />single age class. The scope and magnitude of the observed landslide activity was within the <br />expected range for this area based on terrain, location and underlying geology. <br />4.1.4 Soils <br />Surface soils in the Potential Project area are mapped in two separate reports: Soil Survey of <br />Grand Mesa — West Elk Area, Parts of Delta, Garfield, Gunnison, Mesa and Montrose Counties <br />and Soil Survey of Paonia Area, Parts of Delta, Gunnison, and Montrose Counties (see <br />Figure 6). The West Fork Terror Creek channel in the Potential Project area is covered by two <br />mapped soil units: 158 Herm - Fughes -Kolob family complex, 25 to 40 percent slopes, and 39 <br />Fughes loam, 25 to 65 percent slopes (see Figure 6). <br />121- 014.000 Wright Water Engineers, Inc. Page 4 <br />January 2013 <br />