2010-12-17_REVISION - C1981019 (142)

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Baseline Survey of Soil Resources - Collom Mining Area July, 2006 I suitability thresholds for both boron and selenium in topsoil (WDEQ, 2004). All soils sampled fall below the recommended limit of S.0 ppm for boron while one sample (0825-R01, 14-30 inches, Campspass - 0.12ppm) minimally exceeded the marginal threshold of 0.1 ppm selenium. These results do not support the need for further analysis, as it appears boron and selenium are found in low concentrations in the parent materials of the Survey Area. Soil Map Unit Descriptions The soil survey identified 62 separate map units comprised of series, families, and other more generally classified soils with broader ranges of characteristics. These map units are presented in Appendix B, Table B-5. The map showing the distribution of the map units is presented in Appendix D as I I Frames at a scale of 1:4,800. The dominant composition of each unit is provided along with general information related to the topographic setting, inclusions, and recommended salvage depths. The recommended salvage depths are preliminary and are based on the suitability criteria presented in the POS, field observations, and an understanding of the probable variability based of the factors influencing pedogenesis in the area. These depths and limiting characteristics should be further reviewed and evaluated in the context of reclamation objectives following development of the mine plan. Soil map unit and plant community correlations can be determined by comparing the results of this survey with the Collom Mining Area Baseline Vegetation Survey prepared by Cedar Creek Associates (2006). Soil Salvage Recommendations The topsoil and subsoil horizons in the Survey Area exhibit the most alteration from the parent material and are the substrates most suitable for use as plant growth media. The topsoil generally exhibits more loamy textures, fewer coarse fragments, higher organic matter content, and higher nutrient C concentrations than the subsoil and may warrant segregated salvage and storage where conditions permit. Each of the soil pedon descriptions were reviewed to determine the optimum salvage depth at each location. These depths were then used to identify the observed range and average salvage depth for each of the soils in the Survey Area. These depths are provided in Appendix B, Table B-6. These observations were further used to identify the probable depths of optimal topsoil and subsoil salvage in each of the map units, as shown in Appendix B, Table B-5. The primary physical properties limiting salvage include high clay content and high coarse fragment content. Soils on the ridge tops, especially the Campspass series, have extremely high clay concentrations in the subsoil that may warrant special consideration for reclamation planning. High percentages of coarse fragments are generally uncommon in the intervals proposed for topsoil salvage. However, many series' subsoils, especially those classified as skeletal, have high volumes of coarse fragment. While some of the soils exhibit moderate susceptibility to water erosion and others exhibit high susceptibility to wind erosion, these factors alone are not expected to significantly limit their use in reclamation. The primary chemical property limiting salvage is nutrient content. Nutrient content is variable throughout the Survey Area, but the pachic Mollisols in the southern portion of the Survey Area exhibited the highest nutrient levels and other qualities that make them suitable as plant growth media. Relative to soils from the swales, valleys, and plateaus in the middle and southern portion of the Survey Area, soils in the aridic moisture regime and the northern valley bottoms have low nutrient content and are also often less suitable at shallow depths. Materials proposed for salvage in Appendix B, Tables B-5 and B-6 can be expected to promote vegetative growth, hydrologic function, long-term nutrient cycling, and erosional stability in the reclaimed landscape relative to deeper materials. However, the need for salvage to the maximum depth of available material will depend on the reclamation plan and the suitability of re-graded spoil in the re-graded landscapes. As such, the recommended depths may not be appropriate where more or less soil replacement is required to reclaim disturbances. • Tetra Tech, Inc. 13