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Appendices 6-3 and 6-4 of Tab 6. Analytical data associated with Wolf Creek and Sage Creek overburden and underburden is presented in Tables 6-7A through 6-7D, and Appendix 6-3 of Tab 6. Summary tables and text delineating unsuitable zones and addressing mitigative measures for unsuitable zones within Wadge, Wolf Creek and Sage Creek overburden and underburden are included in Appendix 6-5. Wadge Overburden/Underburden Assessment In 4% or less of the samples analyzed, pH, acid/base potential, boron, manganese, cadmium and zinc exceeded suspect levels. In general, the Division concurs with the applicant's determination that normal mixing of overburden will mitigate the toxic effects of these materials. D.J. Dollhopf in "Selective Placement of Strip Mine Overburden in Montana" (Chapter 5, Summary Report, 1981) suggests that if the volume of toxic material is less than 15% of the total volume of material to be replaced, dilution of the toxic material can be successful. Two primary concerns identified by the Division as a part of the PR-1 review were in regard to potentially acid forming materials associated with the Lennox coal seam and excessive clay contents associated with shale strata overlying the Lennox. The Division requested Seneca to prepare a spoil sampling plan and mitigation plan for areas where the Lennox would be spoiled, and for areas where the Lennox would potentially be exposed by highwall reduction. Amore detailed mitigation plan for areas of excessive clay content was also requested. Seneca submitted an acceptable sampling plan to be employed in areas potentially affected by Lennox spoil or outcrop within the original permit area. The same sampling plan will be applied to all regraded spoil areas and graded fmal highwalls in the south extension mining block. The plan calls for samples to be taken on 500 foot centers within the designated area, and analyzed for clay content, pH, and acid-base potential. Mitigation will include additional sampling to define the area of concern, deep ripping of areas of unsuitable clay content and amendment or burial of acid forming material with a minimum of four feet of suitable material as cover. Nitrate-nitrogen levels were excessive in 14 % of the overburden core samples taken at the Seneca II-W Mine. The locations of the holes which exhibited elevated levels were distant from one another. Furthermore, the stratigraphic location of the elevated nitrate-nitrogen samples are not correlative. Due to the vertical and horizontal distances between locations containing elevated nitrate-nitrogen levels, percolating ground water will not be adversely affected. The dilutional effects of a predicted spoils aquifer should buffer the concentration of nitrate as nitrogen by the time the aquifer discharges to the surface system. Seneca II-W Findings Document 27 November 17, 2004 Permit Revision No. 4