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Baseline Survey of Soil Resources - Collom Mining Area July, 2006
<br />Wind Erodibility
<br />The soil surface layer's texture, organic matter content, carbonate reaction, mineralogy, and coarse
<br />fragment content are factors affecting soil loss due to wind erosion (USDA 2003). Clay content, organic
<br />matter, and coarse fragment content decrease wind erodibility, whereas silty and fine sandy surface materials
<br />are the most prone to wind erosion.
<br />While many of the soils in the Survey Area are in a fine textural family, many have much more loamy surface
<br />textures. This is primarily a result of the notable loess influence on soils throughout the Survey Area. Those
<br />soils with the most notable loess influence, including Shawa, Maudlin, Weed, Skyway, and Lamphier, are all
<br />highly erodible by wind. In the absence of moisture, these soils may begin to erode and may be difficult to
<br />stabilize once exposed. The deep blowouts created in areas of intense traffic on ridges in the
<br />southwestern portion of the Survey Area are evidence of this erodibility. Care should be taken when
<br />salvaging and replacing these soils to limit their exposure to wind.
<br />Water Erosion
<br />The K-factor quantifies susceptibility of soil to erosion by water, with higher values indicating greater
<br />susceptibility. The fine sand and silt fractions of soil are most susceptible to erosion while organic matter
<br />and coarse fragments reduce susceptibility to erosion. Water erosion hazard is based on a soil-erodibility
<br />factor (K-factor) which is determined by the percentage of silt, clay, very fine sand, and organic matter of
<br />the surface horizon, soil structure, and profile permeability class. K factors commonly range from less
<br />than 0.05 to over 0.5. If the K-factor is below 0.3, susceptibility to water erosion is low and the soil is
<br />"good" for use in reclamation without limits. However, when the K-factor approaches or exceeds 0.4,
<br />there is notable potential for water erosion from overland flow when it occurs.
<br />While the surface soil is the material initially at risk from runoff and water erosion when a soil is exposed,
<br />soils within the top 12 inches of each site were evaluated to consider the effects of mixing during salvage
<br />C operations. Textural and organic matter values used in the calculation of the K-factor for the soils of the
<br />Survey Area were determined through review of laboratory results. Soil structure and permeability class
<br />were based on field observations. The K-factors were calculated using the soil erodibility equation
<br />presented in the NSSH (NRCS, 2003a). The results of these calculations are shown with other soil
<br />physical properties in Appendix B, Table B-3.
<br />None of the soils tested in the Survey Area had K-factors in excess of 0.4, but several did have values
<br />greater than 0.25, indicating a moderate susceptibility to water erosion. Sites with K-factors in excess of
<br />0.25 were residual and colluvial soils located on ridge crests and steep sloes in the extreme southern end
<br />of the Survey Area, or soils developed on alluvial fans, terraces, and other gentle sloping sites in the
<br />northern portion of the Survey Area. These locations correlate closely to alluvium and other soils formed
<br />in materials weathered from hard sandstones and siltstones in the lower portion of the Williams Fork
<br />Formation and the upper portion of the lies Formation. In light of these moderately high K-factors, it is
<br />advisable to avoid placement of these materials on steep slopes in the post-mine landscape, or ensure that
<br />they are mixed with other less erosive soils.
<br />Soil Chemical Properties
<br />Soil chemical properties evaluated in this survey include acidity and alkalinity (pH), electrical conductivity
<br />(EC), sodium adsorption ratio (SAR), nutrient content, and Boron and Selenium levels.
<br />Soil Acidity and Alkalinity
<br />The acidity and alkalinity of soils in the Survey Area are closely tied to the parent materials, topographic
<br />position, and moisture regime. Soils developed in alluvial parent materials in frigid aridic and ustic regimes
<br />(e.g.., Adderton, Havre, and Battlement) all had average pH levels above neutral (neutral pH = 7). Other
<br />soils developed primarily from residuum, slope colluvium and loess in cryic and ustic regimes (e.g., Waybe,
<br />Rhone, Maudlin, Thornburgh) all had average pH values below neutral. Soils developed from alkaline
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<br />Tetra Tech, Inc. 11
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