2008-09-29_PERMIT FILE - C1981019A (12)

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RULE 4 PERFORMANCE STANDARDS 4.14 Backfilling and Grading 4.14.1 General Requirements The mining operations of Colowyo will not employ the use of contour mining methods. The following sample of 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 20% swell factor for planning purposes. Dragline swell is estimated to be 23%, and truck/shovel swell is estimated to be 17%. Approximately 45% of the overburden is removed by dragline, and 55% 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), 20% 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 (1988), 20% swell factor 356 feet+ 20% swell = final thickness = 1.05 363 feet+ 49 feet initial thickness The original permit application utilized at 17% swell factor to project the anticipated postmining topography. During the initial permit review process the anticipated swell factor was subsequently revised to 23% 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 20% swell factor for estimating purposes. As indicated in the Annual Reports, the stripping accomplished by draglines can vary from 40% to 45% and from 55% to 60% for truck/shovel. Swell factor will continue to be monitored and the postmining topography adjusted, if necessary. Any adjustments will be minor, will be done gradually and will not affect the reclamation plan or postmining land use. Particularly, drainage channel gradients will not be changed; an entire drainage channel elevation could possibly be revised, but the gradient would remain as designed. If a change would be necessary, the dump plan elevations would be revised as appropriate. In order to verify accuracy of the overburden swell factor predictions and postmining topography projections in the initial permit term, Colowyo has committed to the following requirements: "The applicant has committed, within the application to monitor the topographic configuration of the pit and the postmining reclaimed surface of the mined area, in order to verify the accuracy of the overburden swell factor and postmining topography projections. As specifie4d in the application, monitoring for these purposes shall consist of annual survey, utilizing field survey or aerophotogrammetric methods approved by the Division. Using maps depicting the annual Rule 4 Performance Standards 4.14-1 Revision Date: 6/23/08 Revision No.: MR-91