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depositional environments of the coal-bearing strata of the Dakota Formation. Although <br /> lateral and vertical variability exist, certain distinct physiochemical differences are <br /> apparent between and within some of the Phase I and Phase II sample sites, especially for <br /> the parameters pH and acid-base potential; sand, silt, and clay contents, cation and anion <br /> dominance; sulfur type, and sodium adsorption ratio. The six lithologic units identified <br /> for the Nucla East study area are very similar to previous lithologic units formulated for <br /> Mine Areas 2 and 3. As discussed in the Mixing and Mitigation of Marginally Suitable to <br /> Unsuitable Material section and Tab 21 , Minesoil Reconstruction, only pH and acid-base <br /> potential will impact overall spoil suitability. In most instances, avoidance and normal <br /> overburden mixing will effectively dilute and mitigate potentially inimical zones as <br /> documented in Appendix 6-5. <br /> The major or significant concern within the Nucla East study area is the active and <br /> potential acidity associated with lithologic Units 2 and 4. Sodium concentrations (SAR) <br /> are unsuitable in the southwestern portion of the study area, however, these areas will <br /> not be disturbed by mining. Approximately 83 percent of the overburden and interburden <br /> strata, predominantly consisting of Units 1 and 3, was classified as suitable and would be <br /> potentially available as a topdressing medium. <br /> 6-1-40 Revised 04/11/88 <br />