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TABLE 1, SCS CURVE NUMBERS <br />COVER <br />COVER TYPE <br />HYDROLOGIC <br />PERCENT <br />Hyd. <br />CURVE <br />CURVE <br />CURVE <br />CONDITION <br />VEG. <br />Soil <br />NUMBER, <br />NUMBER, <br />NUMBER, <br />COVER <br />Group <br />HISTORIC " <br />TR -73 <br />CURRENT <br />Undisturbed <br />Mountain Shrub <br />Good <br />85 <br />C <br />41 <br />57 <br />All areas <br />61 <br />All areas <br />Oak -Aspen <br />Good to Fair <br />50-85 <br />C <br />41 <br />57 <br />57 <br />All areas <br />Sagebrush <br />Good <br />85 <br />C <br />47 <br />47 <br />47 <br />All areas <br />Sagebrush <br />Fair <br />50 <br />C <br />63 <br />63 <br />63 <br />Disturbed All areas <br />Topsoil <br />Bare <br />N/A <br />B <br />91 <br />85 <br />85 <br />stripped, roads <br />Spoil piles <br />Bare <br />N/A <br />B <br />did not <br />did not <br />74 Z, <br />& active pit <br />exist <br />exist <br />Reclaimed <br />Topsoiled and <br />Bare <br />N/A <br />B <br />86 <br />83 <br />Prospect Basin <br />seeded <br />83 <br />All other areas <br />80 3) <br />Prospect Basin <br />1 to 2 year <br />Fair — Good <br />25 -45 <br />B <br />61 <br />77 <br />77 <br />All other areas <br />growth <br />74 41 <br />Prospect Basin <br />3+ year growth <br />Fair — Good <br />70+ <br />B <br />56 <br />74 <br />74 <br />All other areas <br />1 <br />62 51 <br />Sources: - Table 8, attached, derived from National Engineering Handbook (NEH -4) (USDA -SCS, 1985) <br />- Undisturbed lands are assumed HSG C, based on SCS county mapping units; except for Prospect drainage disturbed lands are <br />HSG B based on measured infiltration rates reported in Striffler and Rhodes, 1981 in conjunction with Part 630 NEH, Chapter <br />7, Hydrologic Soil Groups. For Prospect Drainage, all CNs, disturbed and undisturbed, are as per TR -73 and generally assume <br />HSG C. <br />- Curve numbers presented in the "Historic" and "TR -73" columns represent previously agreed upon values between DRMS and <br />Colowyo. <br />Notes: 1) Designs certified prior to 2009 were in general based on these CNs <br />2) This CN applies only to tributary portions of active pit area, which are significantly roughened and contain numerous large <br />equipment induced local depressions. Active pit areas where all runoff is captured within the pit are not included in modeled <br />runoff calculations. CNs for tributary active pit and spoil pile areas are considered as "Cultivated land, without conservation <br />treatment" with HSG B, in Table 7 <br />3) CN based on an average of "Fallow, with Crop Residue, Poor Condition ", Table 8, with 50% HSG A and 50% HSG B <br />4) CN based on an average of "Pasture or Range, Fair Condition ", Table 7, with 50% HSG A and 50% HSG B <br />5) CN based on an average of "Pasture or Range, Good Condition ", Table 7, with 50% HSG A and 50% HSG B, conservatively <br />revised upward. <br />Exhibit 7 Page 4 Revision Date: 3/18/13 <br />Revision No.: TR -95 <br />