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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. This <br /> map depicts the expected configuration of the permit area at the end of 2022. The postmining topography <br /> map was developed using actual topography from aerial surveys in October 2019, along with engineering <br /> estimates of material movement from 2019 through 2022. Map M-14A includes a series of cross-sections <br /> that provide a comparison of pre and post mining topography in the active mining area for the current permit <br /> term (2018-2022). <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 re-contouring 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 are <br /> more precisely designed, and thus cause some deviation from the map as presented. Cut lengths may be <br /> affected as a result of better or worse economic conditions which affect the economic stripping limit, or as <br /> a result of differences between inferred coal oxidation limits from existing drill data versus the actual limits <br /> encountered when mined. <br /> If changes in cut lengths occur, the locations of the pits as of December 2022 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 other <br /> factors such as changes in the characteristics of the overburden and interburden which in turn affect digging <br /> rates or by changes in scheduled digging times resulting from labor or equipment problems. These <br /> influences could cause an increase or decrease in the areas requiring regrading as compared to those <br /> shown on Map M12. Regrading areas depicted on Map M12, Postmining Topography,and Map M10 series, <br /> represent regrading under maximum production. <br /> As explained in section 3.1.4.1, a permanent fill resulting from K pit truck/loader operations was constructed <br /> in the Horse Gulch drainage area. This fill resulted in a raised topography in the affected area. The fill <br /> location is shown on Map M10A. The postmining configuration is shown on Map M12. Final geotechnical <br /> designs for the Horse Gulch fill are included in Appendix T. A description of the fill is explained below. <br /> Horse Gulch Fill <br /> Mining of K Pit with a truck and loader fleet required the use of a head of hollow fill capable of storing <br /> approximately 24.6mm BCY of excess spoil. The fill was necessary to ensure the safety of men and <br /> equipment during mining operations. Spoil placed upslope of the active T/L fleet could have potential to <br /> fail, moving downslope onto the T/L or coal loading operations. <br /> 3-40 <br /> Revision: TR-126 <br /> Approved: <br />