2019-11-22_REVISION - C1981019 (2)

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RULE 4 PERFORMANCE STANDARDS 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 specified 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 surveyed configuration of the pit and reclaimed areas,the permittee will determine the overall overburden swell and the resultant variation between premining and post-mining topographic elevation for the mined areas. Further, the permittee will ascertain,record and report to the Division the proportions of overburden excavated using truck/shovel and dragline methods. The maps and a report presenting the methodology and results of the required determinations will be submitted to the Division Rule 4 Performance Standards 4-42 Revision Date: 11/18/19 Revision No.: MR-211