2021-01-28_GENERAL DOCUMENTS - C1982057

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3. Analytical data associated with Wadge overburden and immediate underburden are presented in Tables 6-4 through 6-7, and Appendices 6-3 and 6-4 of Tab 6. Analytical data associated with Wolf Creek and Sage Creek overburden and underburden are presented in Tables 6-7A through 6-71), 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 when the volume of toxic material is less than 15% of total volume to be replaced, dilution of the toxic material can be successful. Two primary concerns identified by the Division as a part of the PR1 review regarded potentially acid forming materials associated with the Lennox coal seam and excessive clay contents associated with shale strata overlying the Lennox. The Division requested that SCC prepare spoil sampling and mitigation plans for areas where the Lennox would be spoiled or,would potentially be exposed by high wall reduction. The Division also requested a detailed mitigation plan for areas of excessive clay. SCC submitted an acceptable sampling plan for areas potentially affected by Lennox spoil or outcrop within the original permit area. The plan specified taking samples on 500 foot centers within the designated area, and analyzed for clay content, pH, and acid-base potential. Mitigation included 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. The regraded areas were sampled during reclamation as required, and all of the samples indicated no mitigation would be required. Nitrate/nitrogen levels were excessive in 14%of the overburden core samples taken at the Seneca IIW Mine. The locations of the holes exhibiting elevated levels were distant from one another. Furthermore, the stratigraphic locations of elevated nitrate/nitrogen samples are not correlative. Due to the vertical and horizontal distances between locations with 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. Wolf Creek/Sage Creek Overburden/Underburden Assessment Only two parameters (iron and lead)exhibited unsuitable levels within sampled increments from the one bore hole that penetrated the sequence in the south extension area. Within each of four delineated intervals (Sage Creek, Upper Wolf Creek, and Lower Wolf Creek overburdens, and Wolf Creek underburden),composite samples were taken from each 10 foot depth increment. The average value for lead within the Lower Wolf Creek overburden interval was in the unsuitable range, due to a very high value within one of five sampled increments. One or more sample increments within the Sage Creek and Wolf Creek overburden intervals exhibited unsuitable iron levels, but the average iron level within each interval was suitable. One of six sampled increments in the Upper Wolf Creek overburden was in the unsuitable range for lead,but the average value for the Page 17 of 37