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criteria used for comparison and relative degrees of suitability are listed in Volume <br />2, Tab 6, Table 6-3, Page 6-21 through 6-24 of the permit application. <br />In 4% or less of the samples analyzed, pH, acid/base potential, boron, manganese, <br />cadmium and zinc exceeded suspect levels. In general, the Division concurs with <br />the applicant's determination that normal mixing of overburden will mitigate the <br />toxic effects of these materials. D.J. Dollhopf in "Selective Placement of Strip Mine <br />Overburden in Montana" (Chapter 5, Summary Report, 1981) suggests that if the <br />volume of toxic material is less than 15 % of the total volume of material to be <br />replaced, dilution of the toxic material can be successful. <br />Two primary concerns identified by the Division as a pazt of the PR-1 review were <br />in regazd to potentially acid forming materials associated with the Lennox coal seam <br />and excessive clay contents associated with shale strata overlying the Lennox. The <br />Division requested Seneca to prepare a spoil sampling plan and mitigation plan for <br />areas where the Lennox would be spoiled, and for aeeas where the Lennox would <br />potentially be exposed by highwall reduction. Amore detailed mitigation plan for <br />areas of excessive clay content was also requested. <br />Seneca submitted an acceptable sampling plan to be employed in aeeas potentially <br />affected by Lennox spoil or outcrop. The plan calls for samples to be taken on 500 <br />foot centers within the designated area, and analyzed for clay content, pH, and <br />acid-base potential. Mitigation will include additional sampling to define the area <br />of concern, deep ripping of aeeas of unsuitable clay content and amendment or burial <br />of acid forming material with a minimum of four feet of suitable material as cover. <br />Nitrate-nitrogen levels were excessive in 14% of the overburden core samples taken <br />at the Seneca II-W Mine. The locations of the holes which exhibited elevated levels <br />were distant from one another. Furthermore, the stratigraphic location of the <br />elevated nitrate-nitrogen samples are not correlative. Due to the vertical and <br />horizontal distances between locations containing elevated nitrate-nitrogen levels, <br />percolating ground water will not be adversely affected. The dilutional effects of a <br />predicted spoils aquifer should buffer the concentration of nitrate as nitrogen by the <br />time the aquifer dischazges to the surface system. <br />Based on data included in annual reclamation reports, spoils exhibiting acid forming <br />potential or excessive clay content have not been replaced on the surface. No <br />indication of the presence of acid forming or otherwise deleterious regraded spoil <br />has been found by the Division during mine inspections. <br />Pursuant to 4.05.8(3), temporary storage of acid or toxic forming spoil may exceed <br />30 days if the operator demonstrates that burial or treatment is not feasible within <br />30 days due to weather conditions or other specified factors, and will not result in <br />material risk of water pollution or other environmental damage. If deemed <br />Seneca II-W Findings Document 19 November 3, 1999 <br />