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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. <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 C factor <br />Sagebrush 0.070 <br />Mountain shrub 0.080 <br />Grassland 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 0.010 has been adopted for <br />the reclaimed mined land vegetative cover at Colowyo in the above described <br />methodology reference. <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 was used, given that Colowyo uses drill seeding parallel to the <br />contour. The curve in Fig. 6-2 for 4" to 6" furrows was used, along with the slopes <br />previously calculated for the LS factor to arrive at P factors for each Reclamation <br />Unit in the reclaimed post-mining condition. <br /> <br />Phase I and 11 Bond Release Application 16