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~G Doc Date:12/11/2001 4.14 BACKFILLING AND GRADING IIIIIIIIIIIIIIIIIII 4.14.1 General Requirements The mining operations of Colowyo will not employ the use of contour mining methods. The following sample calculations show that Colowyo does not have thin or thick overburden as defined in Subsection 4.14.4 or Subsection 4.14.5. These calculations represent the approximate conditions found in the field and show that there is always more than enough overburden to reestablish the original elevation. As explained in the 1983 Annual Report, Colowyo currently uses an average 203 swell factor for planning purposes. Dragline swell is estimated to be 233, and truck/shovel swell is estimated to be 173. Approximately 453 of the overburden is removed by dragline, and 553 by truck/shovel. Since all mining at Colowyo was conducted by truck/shovel methods through 1979, the life-of-mine swell factor has continued to increase. Example: 363 feet overburden, 47 feet coal, (these conditions are • found along the western edge of the pit in 1988), 203 swell factor 363 feet + 20$ swell = final thickness = 1.06 363 feet + 47 feet initial thickness Example: 356 feet overburden, 49 feet coal (these conditions are found along the western edge of the pit in late 1988), 203 swell factor 356 feet + 203 swell = final thickness = 1.05 356 feet + 49 feet initial thickness The original permit application utilized a 173 swell factor to project the anticipated postmining topography. During the initial permit review process the anticipated swell factor was subsequently revised to 233 to ensure that the Streeter Fill volume was adequate to allow for sufficient pit development. At that time, excess swell was anticipated to raise the elevation of the postmining topography by about 5.3 feet, compared to the premining topography. As explained above, in 1984, as part of the 1983 Annual Report, Colowyo further refined its estimates based on measurements to date, and currently uses an overall 203 swell factor for estimating purposes. As indicated in the Annual Reports, the stripping accomplished by draglines can vary from 403 to 453 and from 553 to 603 for truck/shovel. Swell factor will 4.14-1