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RULE 4 PERFORMANCE STANDARDS <br /> K`... 5. .. < ,. ..ex N-:•+...tt-...• .. .+. .a•r 4ts rpt ao..lwst�a}tr •.`.•.-.8+w.:"M AwNgYsi+or:. a....•h*• .a . •.., ,c.w.ay. »a,& * ....+.w...s. <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 ensure that the Streeter Fill volume was adequate to allow for sufficient pit development. <br /> At that time, excess swell was anticipated to raise the elevation of the postmining topography by <br /> about 5.3 feet, compared to the premining topography. As explained above, in 1984, as part of the <br /> 1983 Annual Report, Colowyo further refined its estimates based on measurements to date, and <br /> currently uses an overall 20% swell factor for estimating purposes. As indicated in the Annual <br /> Reports,the stripping accomplished by draglines can vary from 40%to 45%and from 55%to 60% <br /> for truck/shovel. Swell factor will continue to be monitored and the postmining topography <br /> adjusted, if necessary. Any adjustments will b..minor, will be done gradually and will not affect <br /> the reclamation plan or postmining land use. Particularly, drainage channel gradients will not be <br /> changed; an entire drainage channel elevation could possibly be revised, but the gradient would <br /> remain as designed. If a change would be necessary, the dump plan elevations would be revised <br /> as appropriate. <br /> In order to verify accuracy of the overburden swell factor predictions and postmining topography <br /> projections in the initial permit term, Colowyo has committed to the following requirements: <br /> "The applicant has committed, within the application to monitor the topographic <br /> configuration of the pit and the postmining reclaimed surface of the mined area, in order <br /> to verify the accuracy of the overburden swell factor and postmining topography <br /> Rule 4 Performance Standards 4-42 Revision Date: 1/22/20 <br /> Revision No.: TR-136 <br />