2011-04-06_REVISION - C2009087 (4)

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Peabody Sage Creek Mine March 2011 SL-1 Phase 11 Bond Release Request • 90 percent of the Cover Standard = 0.90 [0.83 X (24.8) + 0.17 X (89.5)] = 32.2% The 2010 Phase II bond release block (BRB) sampling at thirty random locations resulted in cover data that exceeded 90% of the standard (32.2% allowable cover). The figure for allowable cover in the 2010 Phase II bond release block (BRB) (37.5%) is the result of subtracting tree, shrub and non-herbaceous cover (1.2%), perennial noxious weed cover (0.44%) and "excess annual/biennial cover" (0.5%) from the observed first hit total vegetation cover of 39.6%. The cover value for the Phase II bond release block (BRB) was greater than the cover success standard. The hypothesis of reclamation success was tested using a parametric test of the "reverse null" hypothesis. This was conducted using the following expression (CDRMS 2005 revised rule, 4.15.11 (2)(c)): x-Q tc _ S- x Where: X- = Bond Release Block Sample Mean • Q = 90% of Standard S_ = Standard error of mean [ s / Vn ] X S = Sample standard deviation n = Sample size t, = Calculated t value tt =Tablet value (alpha= 0.2) see Rohlf and Sokal 1969 If t, is greater than the 1-tailed t table value for alpha error probability of .20, with (n-1) degrees of freedom then Ho is rejected, and revegetation was deemed successful. A one-sample t-test of the assertion that the 2010 Phase II BRB allowable cover is indistinguishable from 90% of the standard is as follows: t, = (37.5 - 32.2) /(14.2 / sqrt 30) = 2.044 • Since critical t = 0.854 (one-tailed, alpha = 0.2, 29 do and t, is greater than this critical value, the "reverse null hypothesis" is rejected and reclamation success for Phase II is demonstrated. 10