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3.5.3 Post Mining Contours <br />The projected postmining topography of Trapper Mine is shown on Map M12, Postmining Topography. <br />This map depicts the expected configuration of the permit area at the end of 2014, except for temporarily <br />abandoned D/E pit that shows postmining topography after it is filled with utility ash near the end of mine <br />life. The postmining topography map was developed using actual topography from aerial surveys in <br />October 2006, along with engineering estimates of material movement from 2008 through 2012. Map M- <br />14A includes a series of cross- sections that provide a comparison of pre and post mining topography in <br />the active mining are for the current permit term (2008 - 2012). <br />Postmining topography cannot be predicted exactly, however, the best estimate given today's technology <br />is presented. Map M12 is, therefore, an approximation of the recontouring limits with a representation of <br />the shape of the topography that will most likely be produced. However, by March 15th each year of the <br />permit term, Trapper will submit to the Division a map showing actual postmining topography for the <br />previous year. Appendix W will contain each year map. <br />As production fluctuates to reflect changes in economic and natural conditions, the areas requiring <br />regrading may change to a limited extent. Lengthening or shortening of various cuts may occur as they <br />are more precisely designed, and thus cause some deviation from the map as presented. Cut lengths <br />may be affected as a result of better or worse economic conditions which affect the economic stripping <br />limit, or as a result of differences between inferred coal oxidation limits from existing drill data versus the <br />actual limits encountered when mined. <br />If changes in cut lengths occur, the locations of the pits as of December 2012 may also be affected as the <br />progression of the pits is a function of their lengths. The pit locations may also be affected by several <br />other factors such as changes in the characteristics of the overburden and interburden which in turn affect <br />digging rates or by changes in scheduled digging times resulting from labor or equipment problems. <br />These influences could cause an increase or decrease in the areas requiring regrading as compared to <br />those shown on Map M12. Regrading areas depicted on Map M12, Postmining Topography, and Map <br />M10 series, represent regrading under maximum production. <br />As explained in section 3.1.4.1, a permanent fill resulting from K pit truck/loader operations is envisioned <br />for Horse Gulch area. This fill will result in raised topography in the affected area. The fill location is <br />shown on Map M10A. The postmining configuration is shown on Map M12. Final geotechnical designs for <br />the Horse Gulch fill have been submitted and are included in Appendix T. A description of the fill is shown <br />below. <br />Horse Gulch Fill <br />Mining of the K -Pit with a truck and excavator (T /E) fleet will require the use of a head of hollow fill <br />capable of storing approximately 24.6mm BCY of excess spoil. The fill is necessary to ensure the safety <br />of men and equipment during mining operations. Spoil placed upslope of the active T/E fleet could have <br />potential to fail, moving downslope onto the T/E or coal loading operations. <br />3-40 <br />6 /2010 <br />