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2 described in Section 2.04.6 are very similarto 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 />which averages 5 feet at New Horizon 1 Mine compared to about 30 feet within the New Horizon <br />2 permit area. Approximately 83 percent of the overburden and interburden material at New <br />Horizon 2, consisting predominantly of Units 1 and 3, is classified as suitable for root growth and <br />aquifer medium material (Section 2.04.6). Unsuitable material was identified in the lower <br />overburden and interburden (Units 2 and 4) within the proposed disturbance area (Peabody, <br />Appendix 6-5). <br />Acid and Toxic-Forming Materials at New Horizon 2 <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 Horizon <br />2 Study Area). Therefore, some ameliorating activity such as mixing, normal burial, or special <br />handling will be required to replace a suitable four-foot root growth medium and to prevent <br />. leachates and runoff from entering the ground water system or discharging into the surface <br />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 <br />disturbance area boundary described within this application (Map 2.05.4-1, Operations Plan - <br />New Horizon 2) or excessive Dakota coal seam depths. These additional avoided areas <br />comprise about 60 to 65 percent of all unsuitable zones which were identified. <br />Complete mixing of the thicker, calcareous overburden Unit 1 (30.5 feet) and interburden Unit 3 <br />(6.7 feet) with the thinner, acidic overburden/interburden Units 2 (4.5 feet) and 4 (2.9 feet) would <br />produce a suitable alkaline spoil (see Section 2.04.6, Table 2.04.6-10). Partial mixing of alkaline <br />and acidic materials is anticipated during cast blasting, dozer pushing, scraper and shovel/truck <br />handling due to the thinness of Units 2 and 4 and the stratification of alkaline and acidic strata. <br />Normal overburden/interburden handling operations may also effectively bury the acid-forming <br />strata. <br />(Revised 6-is-2ooi~ 2.05.4(2)(d)- 2 <br />