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Vegetative Cover Factor, C <br />This factor depends on the type and the density of vegetation. For the pre - <br />mining condition, three general plant communities were mapped. The "C" factor <br />associated with each has been developed for use in sediment pond design, and <br />is described in Methodologies and Assumptions for Sediment Pond Evaluation, <br />Vol 2 D, Exhibit 7, Introductory Text as well as recent agency guidelines <br />conveyed in CDRMS November 23, 2010 comment review. The value selected <br />for the "grassland" plant community is from Table 5.A.3 of Reference 1) on page <br />18. <br />The three plant communities and their associated "C" factors as adopted in that <br />reference are replicated in the following table: <br />Plant community <br />C factor <br />Sagebrush <br />0.011 <br />Mountain shrub <br />0.005 <br />Grassland <br />0.013 <br />The weighted average "C" factor of the several types of pre- mining cover within <br />each Reclamation Unit was then calculated. <br />For the reclaimed post- mining condition a C factor of 0.007 has been adopted for <br />the reclaimed mined land vegetative cover at Colowyo based on CDRMS <br />guidance in the November 23, 2010 comment review. <br />Conservation Practice Factor, P <br />This factor depends on conservation practice, most notably contour plowing and <br />cultivation. For the pre- mining condition a factor of 0.9 seems to be customary, <br />although it can be argued that a default value of 1.0 may be more appropriate. <br />The higher value implies a higher amount of pre- mining erosion under natural <br />conditions. Nevertheless, this analysis conservatively used the 0.9 factor for the <br />pre- mining condition. For the post- mining condition, the method described in Fig. <br />6 -2 of USDA 1996 could be used, given that Colowyo uses drill seeding parallel <br />to the contour. The curve in Fig. 6 -2 for 4" to 6" furrows was used, along with the <br />slopes previously calculated for the LS factor would produce P factors for each <br />Reclamation Unit on the order of 0.30 to 1.00 in the reclaimed post- mining <br />condition. For simplicity, this factor was ignored for this filing, and a P factor of <br />0.9 used for the pre- mining condition was also used for the reclaimed lands, <br />based on guidance CDRMS provided in their November 23, 2010 comment <br />review letter. This essentially ignores any benefits that contour plowing and <br />seeding may have imparted, which is clearly the most conservative approach. <br />Phase I and 11 Bond Release Application 16 <br />