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2.0 Overburden and Interburden Characteristics <br />Overburden and interburden characteristics for New Horizon 2 are presented in Section 2.04.6, <br />Geology Description. Overburden and interburden suitability and lithologic units for the New <br />Horizon #2 Mine described in Section 2.04.6 are very similar to the shallow overburden units at the <br />New Horizon #1 Mine area. The only significant difference between mine areas is the mean <br />thickness of Unit 1 (Bench 1) which averages 5 feet at New Horizon #1 Mine compared to about <br />55 feet within the New Horizon #2 permit area. Approximately 83 percent of the overburden and <br />interburden material at New Horizon 2, consisting predominantly of Units 1 (Bench 1) and 3. <br />Unsuitable material was identified in the lower overburden and interburden (Units 2 and 4) within <br />the proposed disturbance area (Peabody, Appendix 6-5). <br />3.0 Acid and Toxic -Forming Materials at New Horizon 2 Mine <br />Acid and toxic -forming materials were identified within the New Horizon 2 study area; however, only <br />the acid-forming material occurs within the projected mining disturbance area (Peabody Appendix <br />6-5 and Map 2.04.6-1, Geologic Cross Section and Sample Locations for New Horizon 2 Study <br />Area). Therefore, some ameliorating activity such as mixing, normal burial, or special handling will <br />be required to replace a suitable four -foot root growth medium and to prevent leachates and runoff <br />from entering the ground water system or discharging into the surface water system. No roads will <br />be surfaced with the acid-forming material. Mitigation of all unsuitable zones within the <br />underburden material (five percent of all unsuitable zones which were identified) will be by <br />avoidance, i.e., these zones will not be disturbed by mining activities. Certain areas of overburden <br />and interburden will also be avoided due to the projected disturbance area boundary described <br />within this application (Map 2.05.3-1, Current Mine Plan - New Horizon 2) or excessive Dakota coal <br />seam depths. These additional avoided areas comprise about 60 to 65 percent of all unsuitable <br />zones which were identified. <br />Complete mixing of the thicker, calcareous overburden Unit 1 or Bench 1 (30.5 feet) and <br />interburden Unit 3 (6.7 feet) with the thinner, acidic overburden/interburden Units 2 (4.5 feet) and <br />4 (2.9 feet) would produce a suitable alkaline spoil (see Section 2.04.6, Table 2.04.6-10). Partial <br />mixing of alkaline and acidic materials is anticipated during free dig, dozer pushing, shovel, and <br />August 2013 (PR -08) 2.05.4(2)(d)-2 <br />