Laserfiche WebLink
_2.3 Sample Adleauacv Determination <br />Sampling within each unit (reference area or Phase II) was conducted to a minimum of 20 or 33 <br />samples per unit. From these preliminary efforts, sample means and standard deviations for total non - <br />overlapping vegetation ground cover were calculated. For non - monitoring applications, the typical <br />procedure is that sampling continues until an adequate sample, n m i n , has been collected in accordance <br />with the Cochran formula (below) for determining sample adequacy, whereby the population is estimated <br />to within 10% of the true mean (p) with 90% confidence. <br />When the inequality (n <_ n) is true, sampling is deemed adequate; and n min is determined as <br />follows: <br />nmin = ( t 2 2) / (0.1 X )2 <br />where: n = the number of actual samples collected (initial size = 20 or 33) <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 />x = the mean of the estimate as calculated from the initial samples. <br />If the initial samples do not provide a suitable estimate of the mean (i.e., the inequality is false), <br />additional samples would be collected until the inequality (n 5 n) becomes true. <br />2.4 Success Evaluation <br />Success evaluations involve a direct comparison (and where necessary statistical testing) of the <br />ground cover parameter. In the case of ground cover, comparisons are made against reference area <br />data of the same year. There are two methods in which reference area comparisons can be made. The <br />first is a perennial cover comparison in which annual and biennial cover is completely deleted from <br />vegetation cover values. Implementation of this method requires noxious weeds and annual and biennial <br />cover to be removed from the total Phase II cover data set as well as the two reference areas. Perennial <br />cover is the remaining data and can be used in a direct or statistical reference area comparison. <br />CEDAR CREEK ASSOCIATES, Inc. Page 7 Colowyo Coal Company <br />2007 Phase II Evaluation (Updated Dec -10) <br />