2010-12-17_REVISION - C1981019 (142)

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Baseline Survey of Soil Resources - Collom Mining Area July, 2006 bedrock (carbonate cemented sedimentary materials) under an ustic regime in the central portion of the Survey Area generally have the most neutral of all soils. This correlation is reflective of three factors: I) soils at higher elevations likely experience more leaching, which removes carbonates from the soil and lowers pH; 2) The loess that influences many of the high elevation soils does not appear to have had a strong carbonate component; 3) Soils in the northern portion of the Survey Area are in an aridic moisture regime that leads to high carbonate accumulation at shallow depths. The pH of all samples tested ranged from 5.6 to 8.8 and averaged 7.04. While this range is broad, it is unlikely that pH is a significant limiting factor for use in reclamation, except where obvious accumulations of carbonates (e.g., aridisols) are evident in the deep subsoil. Electrical Conductivity A soil's EC is a measure of the salt content of the soil (measured as mmhos/cm) and is directly related to osmotic potentials and water availability. Soils with an EC less than 8.0 mmhos/cm are generally considered non-limiting. Of the soils sampled in the Survey Area, only two samples exceeded this threshold and almost all of the other samples were below 2.0 mmhos/cm. Those samples with the highest EC, including those that exceeded 8.0 mmhos/cm, were taken deep in the profile (20 to 40 inches below ground surface) of soils with high clay content (Cochetopa, Morapos, and Campspass). Often the high clay content would make these soils unsuitable for salvage regardless of the conductivity. EC is not a notable limiting factor in the Survey Area. Sodium Adsorption Ratio The SAR of the soil is a measure of soil sodicity, which degrades soil structure and inhibits plant growth at C higher levels. Levels above 8.0 can be limiting and may cause surface crusting. Levels above 12 are further limiting and may require treatments with amendments to revegetate. The SAR of most soil sampled was less than 2.0 with only three exceeding 8.0 and none exceeding 12. All of the soils with an SAR over 8.0 were taken from below 24 inches in the soil profiles. Most of the soils with the highest SAR (Cochetopa, Campspass, and Yamo) were also observed to have high EC. These results indicate that SAR is not a notable limiting factor in the Survey Area. Nutrient Content The nutrient content of native (non-cropland) soils is generally low, and therefore there are not strict guidelines for determining limitations. However, data from the various series across the Survey Area provided a reference base to compare within. Phosphorus content ranged from 0.03 to 34 milliequivalents per liter (meq/L) and averaged six (meq/L). The soils with the lowest phosphorus levels were the Aridisols (Forelle, Yamo, etc.) while the highest phosphorus levels were found in Lamphier, Campspass, and Weed soils. Potassium levels ranged from 11.3 to 1430 (meq/L) and averaged 276 (meq/L). Potassium was found at the highest levels in the Rhone, Lamphier, and Shawa series and lowest levels in the Danavore and Yamo series. Available nitrogen levels ranged from 0.02 to 35.8 (average = 2.52) with the most nitrogen available (on average) found in Rhone and similar soils. No series was especially low in nitrogen content. Soil organic matter is a critical source of nutrients in native soils and often accounts for low free nutrient levels. Soil organic matter ranged from to 0.3 to 9.6 percent and averaged 3.13 percent. The Aridisols and Entisols exhibited the lowest organic matter content, while the pachic mollisols, Rhone, Lamphier, and Cochetopa series had the highest content. Boron and Selenium Concerns over boron and selenium content in mine soils prompted testing of background levels in the Survey Area. The soils tested revealed boron concentrations ranging from 0.07 to 1.34 parts per million (ppm) and averaging 0.39 ppm. Selenium levels range from less than 0.02 to 1.0 ppm with most registering below the detection limit. The WDEQ Topsoil and Overburden Guidelines specify recommended Tetra Tech, Inc. 12