2011-04-06_REVISION - C2009087 (4)

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Peabody Sage Creek Mine SL-1 Phase 11 Bond Release Request u 0 Table 2, Sample Adequacy Summary for Total First Hit Cover March 2011 Area Total First Hit Cover (x) s N nmin t Phase II Bond Release Block 39.6 14.3 30 23 1.311 Mountain Brush RA 71.5 7.4 15 2 1.345 Sagebrush RA 71.1 7.8 15 3 1.345 Table 3, Sample Adequacy Summary for Allowable First Hit Herbaceous Cover Area Allowable First Hit Herbaceous Cover (x) s N nm;,, t Phase II Bond Release Block 37.5 14.2 30 25 1.311 Mountain Brush RA 12.4 5.1 15 29 1.345 Sagebrush RA 44.7 8.8 15 8 1.345 Final ratio-adjusted cover value used in weight averaged standard is 12.4. See below. The lack of sample adequacy for the mountain brush reference area using allowable first hit herbaceous cover necessitated an approach using a series of adjustments and calculations to arrive at an adequate sample and final determination of the allowable first hit herbaceous cover value for establishing the cover standard. The historical cover success standard developed for the Seneca II Mine and which applies to PSCM is an area- weighted average of first hit herbaceous cover values determined from the mountain brush and sagebrush reference areas. Further, the first hit cover is adjusted to allowable as discussed previously. In recent years it was required by CDRMS to perform sample adequacy using first hit herbaceous cover data. In the mountain brush, achieving sample adequacy using first hit herbaceous cover data results in very high sample numbers as a result of high variability. The mountain brush structure is dominated by a rather dense woody canopy, but may also have some areas of relatively open canopy to the herbaceous • understory. These characteristics contribute to the highly variable first hit herbaceous cover 8