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2.4 Sample Adeauacv Determination <br /> Cover, production, and woody plant density sampling within each unit was conducted using 30, 45, <br /> and 60 or 82 points, respectively. Cover and production sampling points were co-located, woody plant <br /> density sample points were laid out on a unique grid. From these preliminary efforts, sample means and <br /> standard deviations for total non-overlapping vegetation ground cover, total production, and wood plant <br /> density were calculated. The Cochran formula (below) for determining sample adequacy was used to <br /> calculate nmin, whereby the population is estimated to within 10% (cover and production) or 15% (woody <br /> plant density) of the true mean (p) with 90% confidence. <br /> When the inequality (nmin <_ n) is true, sampling is deemed adequate; and nmin is determined as <br /> follows: <br /> nmin = (t 25 2) / (d X )2 <br /> Where: n = the number of actual samples collected (initial size = 30, 45, 60, or 82) <br /> t = the value from the one-tailed t distribution for 90% confidence with n-1 <br /> degrees of freedom; <br /> s 2 = the variance of the estimate as calculated from the initial samples; <br /> d = precision (0.10 for cover and production; 0.15 for woody plant density); <br /> x = the mean of the estimate as calculated from the initial samples. <br /> 2.5 Success Comparisons <br /> Rule 4.15.11 (2)(a) of the Colorado Coal Regulations allows for direct comparison of cover and <br /> production values if sample adequacy is demonstrated and a minimum of 15 transects in each unit is <br /> collected (as in 2019 and 2021). If adequacy is not met,various forms of null and reverse null hypothesis <br /> testing based on the mean may be employed to demonstrate success which do not require adequacy. <br /> Rule 4.15.11 (3)(b)(i) of the Colorado Coal Regulations allows for direct comparison of woody plant <br /> density values if a minimum of 75 >_100 mz transects in each unit is collected (as in 2021). In lieu of a <br /> direct comparison, Rule 4.15.11 (3)(a) allows the use of a reverse null ranked "L" test to demonstrate <br /> success. In this approach, success is demonstrated when the lower 80% confidence limit of the reclaimed <br /> area median is >70% of the relevant success standard (or 90% of the technical standard according to TR- <br /> 63) with a minimum sample size of 30 (as in 2019). <br /> CEDAR CREEK ASSOCIATES, Inc. 9 Bowie #1 Mine-West Mine - 2021 <br /> Phase III Bond Release Evaluation <br />