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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 80 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 80) <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 2020). 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 2020). 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 - Run of Mine - 2020 <br />Phase III Bond Release Evaluation <br />