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and others). The criteria used for comparison and relative degrees of <br />suitability are listed in Volume 2, Tab 6, Table 6-3, Page 6-21 through 6-24 <br />of the permit application. <br />In 4% or less of the samples analyzed, pH, acid/base potential, boron, <br />manganese, cadmium and zinc exceeded suspect levels. In general, the <br />Division concurs with the applicant's determination that normal mixing of <br />overburden will mitigate the toxic effects of these materials. D.J. Dollhopf <br />in "Selective Placement of Strip Mine Overburden in Montana" (Chapter 5, <br />Summary Report, 1981) suggests that if the volume of toxic material is less <br />than 15% of the total volume of material to be replaced, dilution of the <br />toxic material can be successful. <br />Two primary concerns identified by the Division as a part of the PR #1 <br />review were in regard to potentially acid forming materials associated with <br />the Lennox coal seam and excessive clay contents associated with shale <br />strata overlying the Lennox. The Division requested Seneca to prepaze a <br />spoil sampling plan and mitigation plan for areas where the Lennox would <br />be spoiled, and for areas where the Lennox would potentially be exposed by <br />highwall reduction. Amore detailed mitigation plan for areas of excessive <br />clay content was also requested. <br />Seneca submitted an acceptable sampling plan to be employed in areas <br />potentially affected by Lennox spoil or outcrop. The plan calls for samples <br />to be taken on 500 foot centers within the designated area, and analyzed for <br />clay content, pH, and acid-base potential. Mitigation will include additional <br />sampling to define the area of concern, deep ripping of areas of unsuitable <br />clay content and amendment or burial of acid forming material with a <br />minimum of four feet of suitable material as cover. <br />Nitrate-nitrogen levels were excessive in 14% of the overburden core <br />samples taken at the Seneca II-W Mine. The locations of the holes which <br />exhibited elevated levels were distant from one another. Furthermore, the <br />stratigraphic location of the elevated nitrate-nitrogen samples are not <br />correlative. Due to the vertical and horizontal distances between locations <br />containing elevated nitrate-nitrogen levels, percolating ground water will not <br />be adversely affected. The dilutional effects of a predicted spoils aquifer <br />should buffer the concentration of nitrate as nitrogen by the time the <br />aquifer discharges to the surface system. <br />Based on data included in annual reclamation reports submitted prior to <br />Permit Renewal 02 submittal, spoils exhibiting acid forming potential or <br />excessive clay content have not been replaced on the surface. No indication <br />of the presence of acid forming or otherwise deleterious regraded spoil has <br />been found by the Division during mine inspections. <br />18 <br />