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RULE 4 PERFORMANCE STANDARDS <br /> 4.14 BACKFILLING AND GRADING <br /> 4.14.1 General Requirements <br /> The mining operations of Colowyo will not employ the use of contour mining methods. <br /> The following sample of calculations show that Colowyo does not have thin or thick overburden <br /> as defined in Subsection 4.14.4 or Subsection 4.14.5. These calculations represent the approximate <br /> conditions found in the field and show that there is always more than enough overburden to <br /> reestablish the original elevation. As explained in the 1983 Annual Report, Colowyo currently <br /> uses an average 20% swell factor for planning purposes. Dragline swell is estimated to be 23%, <br /> and truck/shovel swell is estimated to be 17%. Approximately 45%of the overburden is removed <br /> by dragline,and 55%by truck/shovel. Since all mining at Colowyo was conducted by truck/shovel <br /> methods through 1979, the life-of-mine swell factor has continued to increase. <br /> Example: 363 feet overburden, 47 feet coal, (these conditions are found along the western edge of <br /> 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 edge of <br /> the pit in(1988), 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 postmining <br /> topography. <br /> During the initial permit review process the anticipated swell factor was subsequently revised to <br /> 23% to allow for sufficient pit development. At that time, excess swell was anticipated to raise <br /> the elevation of the postmining topography by about 5.3 feet, compared to the premining <br /> topography. As explained above, in 1984, as part of the 1983 Annual Report, Colowyo further <br /> refined its estimates based on measurements to date,and currently uses an overall 20%swell factor <br /> for 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 will <br /> continue to be monitored and the postmining topography adjusted, if necessary. Any adjustments <br /> will be minor, will be done gradually and will not affect the reclamation plan or postmining land <br /> use. Particularly, drainage channel gradients will not be changed; an entire drainage channel <br /> elevation could possibly be revised, but the gradient would remain as designed. If a change would <br /> be necessary,the dump plan elevations would be revised as appropriate. <br /> Rule 4 Performance Standards 4-34 Revision Date: 12/20/19 <br /> Revision No.: TR-135 <br />