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4.14 BACKFILLING AND GRADING <br />4.14.1 General Requirements <br />The mining operations of Colowyo tivill not employ the use of contour mining methods. <br />The following sample of calculations show that Colowyo does not have thin or thick <br />overburden as defined in Subsection 4.14.4 or Subsection 4.14.5. These calculations <br />represent the approximate conditions found in the field and show that there is always more <br />than enough overburden to reestablish the original elevation. As explained in the 1983 <br />Annual Report, Colowyo currently uses an average 20% swell factor for planning purposes. <br />Dragline swell is estimated to be 23%, and truck/shovel swell is estimated to be 17%. <br />Approximately 45% of the overburden is removed by dragline, and 55% by truck/shovel. <br />Since all mining at Colowyo was conducted by truck shovel methods through 1979, the life- <br />of-mine swell factor has continued to increase. <br />Example: 363 feet overburden, 47 feet coal, (these conditions are found along the western <br />edge of the pit in 1988), 20% swell factor <br />363 feet + 20% swell = final thickness = 1.06 <br />363 feet + 47 feet initial thickness <br />Example: 356 feet overburden, 49 feet coal (these conditions are found along the western <br />• edge of the pit in (] 988), 20% swell factor - <br />356 feet + 20%swell - final thickness = 1.05 <br />363 feet + 49 feet initial thickness <br />The original permit application utilized at 17% swell factor to project the anticipated <br />postmining topography. <br />During the initial permit review process the anticipated swell factor was subsequently revised <br />to 23% to ensure that the Streeter Fill volume was adequate to allow for sufficient pit <br />development. At that time, excess swell was anticipated to raise the elevation of the <br />postmining topography by about 5.3 feet, compared to the premining topography. As <br />explained above, in 1984, as part of the 1983 Annual Report, Colowyo further refined its <br />estimates based on measurements to date, and currently uses an overall 20% swell factor for <br />estimating purposes. As indicated in the Annual Reports, the stripping accomplished by <br />draglines can vary from 40% to 45% and from 55% to 60% for truck/shovel. Swell factor <br />will <br /> <br />4.14-] <br />