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2.0 Overburden and Interburden Characteristics <br />Overburden and interburden characteristics are presented in Section 2.04.6, Geology Description. <br />Overburden and interburden suitability and lithologic units for the New Horizon 2 Mine <br />described in Section 2.04.6 are very similar to the shallow overburden units at the New Horizon <br />1 Mine area. The only significant difference between mine areas is the mean thickness of Unit 1 <br />(Bench 1) which averages 5 feet at New Horizon 1 Mine compared to about 55 feet within the <br />New Horizon 2 permit area. Approximately 83 percent of the overburden and interburden <br />material at New Horizon 2, consisting predominantly of Units 1 (Bench 1) and 3. Unsuitable <br />material was identified in the lower overburden and interburden (Units 2 and 4) within the <br />proposed disturbance area (Peabody, Appendix 6-5). <br />3.0 Acid and Toxic -Forming Materials <br />Acid and toxic -forming materials were identified within the New Horizon 2 study area; however, <br />only the acid-forming material occurs within the projected mining disturbance area (Peabody <br />Appendix 6-5 and Map 2.04.6-1, Geologic Cross Section and Sample Locations for New <br />Horizon 2 Study Area). Therefore, some ameliorating activity such as mixing, normal burial, or <br />special handling will be required to replace a suitable four -foot root growth medium and to <br />prevent leachates and runoff from entering the ground water system or discharging into the <br />surface water system. No roads will be surfaced with the acid-forming material. Mitigation of all <br />unsuitable zones within the underburden material (five percent of all unsuitable zones which <br />were identified) will be by avoidance, i.e., these zones will not be disturbed by mining activities. <br />Certain areas of overburden and interburden will also be avoided due to the projected disturbance <br />area boundary described within this application (Map 2.05.3-1, Current Mine Plan - New <br />Horizon 2) or excessive Dakota coal seam depths. These additional avoided areas comprise about <br />60 to 65 percent of all unsuitable 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) <br />and 4 (2.9 feet) would produce a suitable alkaline spoil (see Section 2.04.6, Table 2.04.6-10). <br />Partial mixing of alkaline and acidic materials is anticipated during free dig, dozer pushing, <br />shovel, and truck fleet handling due to the thinness of Units 2 and 4 and the stratification of <br />alkaline and acidic strata. Normal overburden/interburden handling operations also effectively <br />bury the acid-forming strata. <br />Typical overburden/interburden handling operations are described in Section 2.05.3, Operation <br />Plan and Section 2.05.4(2)(c), Backfilling and Grading. <br />July 2018 (TR -84) 2.05.4(2)(d)-2 <br />