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• percent of the predicted value with 90 percent statistical confidence using aone-tailed <br />Students t statistical test. <br />5.2 Total Herbaceous Production <br />Based on a review of the data and best-fit curves and accompanying equations from both <br />the 2002 investigation and additional data reviewed in this investigation, as well as <br />calculation of predictive values for total herbaceous production over the range of sampled <br />September-July precipitation, it is recommended that the predictive equation originally <br />recommended in the 2002 investigation: y = 5.1676a'~ - 87.19x + 464.85, where x is the <br />value of the cumulative September-July precipitation at the mine and y is the value of the <br />total herbaceous production, be used as a predictive equation to determine total <br />herbaceous production success at the Keenesburg Mine site. As with any revegetation <br />success criteria, revegetation success for this parameter would be deemed demonstrated if <br />the total herbaceous production of the area to be tested is greater than 90 percent of the <br />predicted value with 90 percent statistical confidence using aone-tailed Students t <br />statistical test. <br />5.3 Species Composition <br />As detailed above, the current species composition success criteria is not realistic when the <br />Osgood Sand Reference Area, from which this criterion was developed, cannot meet the <br />• criterion. Based on statistically adequate vegetation cover data taken between 1994 and <br />2004, a new species composition success criterion should be implemented. Any criterion <br />should represent the range, number, and lifeform types of the native vegetation <br />community. The revised criterion is as follows. The species composition on the reclaimed <br />area shall be such that there are at least four perennial species of which three are warm <br />season perennial grasses and one is a cool season perennial grass. No one component of <br />the above four species should comprise greater than 40% relative importance nor less than <br />3% relative importance. Relative importance will be measured by calculating relative <br />cover of the revegetation species. Vegetation species that may be used in the calculation <br />of species composition may be any plant species not defined as a noxious or prohibited <br />plant species, and may be native or introduced. <br /> <br />Coors Energy Company Keenesburg Mine Page 12 <br />2005 Addendum to Revision of Revegetatbn Success Crkeria <br />