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<br />Acid and Toxio-Forming Materials at New Horzon 2 <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 6-5 <br />and Map 2.04.6-1, Geologic Cross Section and Sample Locations for New Horizon 2 Study Area]. <br />Therefore, some ameliorating activity such as mixing, normal burial, or special handling will be required <br />to replace a suitable four-foot root growth medium and to prevent leachates and runoff from entering <br />the ground water system or discharging into the surface water system. No roads will be surfaced <br />with the acid-forming material. Mitigation of all unsuitable zones within the underburden material (five <br />percent of all unsuitable zones which were identrfied] will be by avoidance, i.e., these zones will not be <br />disturbed by mining activities. Certain areas of overburden and interburden will also be avoided due to <br />the projected disturbance area boundary described within this application (Map 2.05.41, Operations <br />Plan -New Horizon 2) or excessive Dakota coal seam depths. These additional avoided areas <br />comprise about 60 to 6S percent of aN unsuitable zones which were identified. The identified <br />unsuitable sodic strata which occurs in the southwestern portion of the study area (Sites 872E and <br />662E) will be avoided entirely. <br />Complete mixing of the thicker, calcareous overburden Unit 1 (30.5 feet) and interburden Unit 3 (6.7 <br />feet) with the thinner, acidic overburden/'interburden Units 2 (4.5 feet] and 4 (2.9 feet) would produce <br />a suitable alkaline spoil (see Section 2.04.6, Table 2.04.6-10). Partial mixing of alkaline and acidic <br />materials is anticipated during cast blasting, dozer pushing, scraper and shovel/truck handling due to <br />the thinness of Units 2 and 4 and the stratification of alkaline and acidic strata. Normal <br />overburden/interburden handling operations may also effectively bury the acid-forming strata. <br />Typical overburden/interburden handling operations are described in Section 2.05.3, Operation Plan <br />and Section 2.05.4(2](c), Backfilling and Grading. The overburden/interburden material excavated by <br />truck and shovel from the cropline pit is placed in box cut spoil stockpiles as shown on Map 2.05.41, <br />Operations Plan -New Horizon 2. Based upon the existing spoil stockpile at New Horizon 1 mine area, <br />the overburden/interburden will likely be stratified by individual distinct lifts of different lithologic <br />material. Lithologic Unit 1 material will typically be placed near the base of the stockpile with a thin <br />topdressing of Units 2, 3, and 4. As the stockpiled material is returned to the final pit, mixed Units 2, <br />3, and 4 will be placed near the pit base and subsequently covered with Unit 1 material. Mixed Units <br />2, 3, and 4 have mean pH and ABP values of 6.0 and -1 .B, respectively, which are both considered <br />suitable for aqurfer or root growth medium material (Section 2.04.6, Table 2.04.6-3). <br />The following overburden/interburden handling techniques are being utilized after the lower Dakota <br />Coal has been removed from the box cut pit. Initially, the upper unconsolidated overburden is removed <br />by shovel and trucks and placed into the adjacent pit void. Cast blasting is being utilized, when <br />possible, to fracture the remaining consolidated overburden/interburden. During cast blasting, <br />2.05.4(2)(d}2 <br />