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Final Grading: Final grading and preparation of the backfilled material before placement of <br />topsoil material will be completed along the contour to minimize subsequent erosion and <br />instability. If such grading is hazardous to equipment operators, then grading will be done in a <br />direction other than generally parallel to the contour. <br />Final Pit Backfilling: In order to eliminate any final highwalls and to achieve the approximate <br />original landform, some highwall material will be pushed or dozed into the mined area. Map <br />2.05.4-2 shows typical cross sections of the fill material placed into the mined pits. Material <br />above the final highwall may be blasted or ripped and then graded to blend into the surrounding <br />topography. <br />Thin and Thick Overburden: The NHN Mine permit area does not meet the requirements of <br />either the thick or thin overburden as shown by the following calculations: <br />96.00' maximum stripping depth <br />55.91' average overburden <br />9.60' Max. Combined Upper and Lower Dakota <br />At the average stripping depth <br />55.91' overburden <br />+ 7.05' coal <br />62.96' material excavated <br />at 15% Swell <br />1.15 x (55.91) = 64.30 material replaced <br />64.30'/62.96' = 1.021 of the initial thickness <br />Therefore, the 0.8 requirement for thin overburden and the 1.2 requirement for thick overburden <br />are not met. <br />At the maximum stripping depth <br />96.00' overburden <br />+ 9.60' coal <br />105.60' material excavated <br />at 15 % Swell <br />1.15 x (96.00') = 110.40' material replaced <br />110.40'/105.60'= 1.045 of the initial thickness <br />Section 2.05.4(2)(c) Page 2 Sept. 2015 (TR -11) <br />