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Coors Energy Company Keenesburg Mine—Phase III Bond Release Application Revegetation Success Demonstration 3.2 Sample Adequacy Sample size was based on either: 1. A minimum of 15 samples with sample adequacy being met; 2. Sampling to a statistically adequate sample size; or 3. Sampling to a maximum of 30 samples. Table 2 and Table 3 present the actual sample size and sample adequacy calculations for each Reclamation Area in 2021 and 2022, respectively.Non-noxious cover was used in the field estimate sample adequacy while allowable cover was used in hypothesis testing. Sample adequacy was calculated using the following formula: t2s2 nmin = (dX)2 where: nmin=Minimum sample size s2= Sample variance (n-1 degrees of freedom) d=Precision(0.10) x = Sample arithmetic mean t=The (a=0.10)t-table value for a 1 tail t-test,n-1 degrees of freedom (infinite degrees of freedom may be used if n>30) n= Sample size Table 2: Area 29/23, 30, and 31 Sample Adequacy 2021 Non-Noxious Cover Allowable Cover Reclamation 1-tailed St. Nmin St. Nmin Area N* t-value Mean Dev. ** Mean Dev. ** Area 29/23 18 1.333 35.9 9.9 14 29.1 9.9 21 Area 30 15 1.345 30.5 8.5 14 27.5 8.5 18 Area 31 15 1.345 37.7 9.6 12 37.7 9.6 12 *N=Sample Size **N-min=Minimum sample size necessary to detect a 10%reduction in the mean with 90%confidence using n-1 degrees of freedom Table 3: Area 29/23, 30, and 31 Sample Adequacy 2022 Non-Noxious Cover Allowable Cover Reclamation 1-tailed St. Nmin St. Nmin Mean Area N* t-value Mean Dev. ** Dev. ** Area 29/23 30 1.311 43.9 13.2 16 18.9 13.1 83 Area 30 24 1.319 31.5 10.8 21 18.7 10.8 58 Area 31 21 ; 1.325 27.4 6 9 22.6 6 13 *N=Sample Size **N-min=Minimum sample size necessary to detect a 10%reduction in the mean with 90%confidence using n-1 degrees of freedom SL-12 6 May 2024