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• Conclusions <br />Overburden characteristics within the New Horizon 2 study area reflect the variable depositional <br />environments of the coal-bearing strata of the Dakota Formation. Although lateral and vertical <br />variability exist, certain distinct physiochemical differences are apparent between and within some <br />of the Phase I and Phase II sample sites, especially for the parameters pH and acid-base potential; <br />sand, silt, and clay contents, cation and anion dominance; sulfur type, and sodium adsorption ratio. <br />The six lithologic units identified for the New Horizon 2 study area are very similar to previous <br />lithologic units formulated for Mine Areas 2 and 3. As discussed in the Mixing and Mitigation of <br />Marginally Suitable to Unsuitable Material section and Section 2.05.4(2)(d), Topsoil (Redistribution), <br />only pH and acid-base potential will impact overall spoil suitability. In most instances, avoidance <br />and normal overburden mixing will effectively dilute and mitigate potentially inimical zones as <br />documented in Peabody Appendix 6-5. <br />The major or significant concern within the New Horizon 2 study area is the active and potential <br />acidity associated with lithologic Units 2 and 4. Sodium concentrations (SAR) are unsuitable in the <br />southwestern portion of the study area, however, these areas will not be disturbed by mining. <br />• Approximately 83 percent of the overburden and interburden strata, predominantly consisting of <br />Units 1 and 3, is classified as suitable and would be potentially available as a top dressing medium. <br />Additional Exploration Drilling <br />As approved via a technical revision in September, 1992, twelve exploratory holes were drilled in <br />order to better define the crop/subcrop boundary. The holes averaged 50 feet in depth, and were <br />5-1/8" in diameter. See Map 2.04.6-6 for the hole locations and access. <br />During 1993, Western Fuels-Colorado, drilled 35 coal exploration holes,(fourteen of which were <br />core drilled) in lands adjacent to the New Horizon 2 mine area. This new data as well as the <br />existing data provide the geologic information for mine planning for this permit revision. <br />Revised 27 Aug 2002 38 <br />