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• appeaz to contradict the empirical data. For these reasons, the best-fit curves from the <br />2002-2004 reclamation areas data do not improve on the predictive ability of the <br />equations from the 2002 investigation. <br />4.5.2 Total Herbaceous Production <br />Calculation of predictive values from the best-fit curves from the 2002 investigation <br />revealed a concern with the equation for the Osgood Sand Reference Area. At the lowest <br />precipitation level the equation predicted a negative result. As total herbaceous <br />production can never be negative in a real world scenario, this automatically disqualifies <br />the equation for consideration as a practical predictive measure of revegetation success. <br />Best-fit curves and corresponding equations from the cumulative data of 2002-2004 for <br />the reference area yielded curves and equations with high correlation coefficients and more <br />reasonable curve shapes, however, inflection points in the mid range of precipitation and <br />especially low predicted values at low precipitation levels brought into question the <br />usefulness of these equations. <br />Total herbaceous production values from the reclamation areas in 2002-2004 resulted in <br />best-fit curves and predictive equations with significantly lower correlation coefficients <br />and less data specific curves as a result of more variable data. These conditions resulted in <br />predicted total herbaceous production values that were higher at low precipitation levels <br />and lower at higher precipitation levels. The predictive equation developed in the 2002 <br />• investigation appears to provide the best correlation, practical curve shape, and predictive <br />values. <br />For these reasons, the best-fit curves from the 2002-2004 reclamation areas or the <br />cumulative data from 2002-2004 from the Osgood Sand Reference Area data do not <br />improve on the predictive ability of the equation from the reclamation azeas in the 2002 <br />investigation. <br />5.0 RECOMMENDATIONS <br />5.1 Total Vegetation Cover <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 vegetation cover over the range of sampled <br />September-July precipitation, it is recommended that the predictive equation originally <br />recommended in the 2002 investigation: ~! = 00.4478a'r + 14.I1x - 63.217, where x is <br />- the value of the cumulative September-July precipitation at the mine and y is the value of <br />the total vegetation cover, be used as a pre~ive equation to determine total vegetation <br />cover revagefation success at the Keenesburg Mine site. As with any revegetation success <br />• criteria, revegetation success for this pazameter would be deemed successfully <br />demonstrated if the total vegetation cover of the azea to be tested is greater than 90 <br />Coors Energy Company Keenesburg Mine Page 11 <br />2005 Addendum to Revision of RevegetaUon Success Criteria <br />