2009-03-04_PERMIT FILE - C1981008A (11)

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• New Horizon 2 Overburden and Interburden Characteristics Overburden and interburden characteristics for New Horizon 2 are presented in Section 2.04.6, Geology Description. Overburden and interburden suitability and lithologic units for New Horizon 2 described in Section 2.04.6 are very similar to the shallow overburden units at the New Horizon 1 Mine area. The only significant difference between mine areas is the mean thickness of Unit 1 (Bench 1) which averages 5 feet at New Horizon 1 Mine compared to about 55 feet within the New Horizon 2 permit area. Approximately 83 percent of the overburden and interburden material at New Horizon 2, consisting predominantly of Units 1(Bench 1) and 3, is classified as suitable for root growth and aquifer medium material (Section 2.04.6). Unsuitable material was identified in the lower overburden and interburden (Units 2 and 4) within the proposed disturbance area (Peabody, Appendix 6-5). Acid and Toxic-Forming Materials at New Horizon 2 Acid and toxic-forming materials were identified within the New Horizon 2 study area; however, • only the acid-forming material occurs within the projected mining disturbance area (Peabody Appendix 6-5 and Map 2.04.6-1, Geologic Cross Section and Sample Locations for New Horizon 2 Study Area). Therefore, some ameliorating activity such as mixing, normal burial, or special handling will be required to replace a suitable four-foot root growth medium and to prevent leachates and runoff from entering the ground water system or discharging into the surface water system. No roads will be surfaced with the acid-forming material. Mitigation of all unsuitable zones within the underburden material (five percent of all unsuitable zones which were identified) will be by avoidance, i.e., these zones will not be disturbed by mining activities. Certain areas of overburden and interburden will also be avoided due to the projected disturbance area boundary described within this application (Map 2.05.3-1, Current Mine Plan - New Horizon 2) or excessive Dakota coal seam depths. These additional avoided areas comprise about 60 to 65 percent of all unsuitable zones which were identified. Complete mixing of the thicker, calcareous overburden Unit 1 or Bench 1 (30.5 feet) and interburden Unit 3 (6.7 feet) with the thinner, acidic overburden/interburden Units 2 (4.5 feet) and 4 (2.9 feet) would produce a suitable alkaline spoil (see Section 2.04.6, Table 2.04.6-10). • (Revised Nov 2008) 2.05.4(2)(d)-6