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Coors Energy Company Keenesburg Mine—Phase II/III Bond Release Application <br /> Sedimentology Demonstration <br /> 2.1 Rainfall Factor(R) <br /> The equation used previously to compute the R factor is as follows: <br /> Average Annual R=27*(P2 6)2 2 <br /> where: <br /> P2,6=2-year, 6-hour precipitation event in inches from published rainfall data <br /> (e.g., Miller, et al 1973). <br /> The 2-year, 6-hour Type II storm event for the Keenesburg, Colorado area was <br /> conservatively identified as 1.4 inches of rainfall. The annual average R factor was then <br /> computed to be 56.6 for both the reclaimed and adjacent undisturbed areas. This number <br /> was used again for the final RUSLE calculations rather than the number generated by the <br /> RUSLE program because it was more conservative. <br /> 2.2 Soil Erodibility Factor(IC) <br /> The soil erodibility factor K is a measure of a soil's susceptibility to erosion. For previous <br /> sedimentology reports at this Keenesburg site, K values were determined for undisturbed <br /> and reclaimed soil conditions using the 1979 Soil Conservation Service (now Natural <br /> Resources Conservation Service) publication, Soils of Colorado: Loss Factors and <br /> Erodibility Hydrologic Groupings. Factor values were established based on K values for <br /> "A", "B", and subsoil horizons salvaged from the Valent and Osgood soils. For reclaimed <br /> and undisturbed conditions K factors of 0.11 and 0.10, respectively, were previously <br /> established and continue to be used in this evaluation. <br /> 2.3 Length Slope Factor(LS) <br /> Slope steepness and length both affect the degree of soil erosion on a given slope surface. <br /> Characteristics for the reclaimed unit were obtained from the slope cross-sections identified <br /> on Figure 1 and summarized in Table 1. The slope cross-section represents the longest slope <br /> in the area. For the reclaimed areas the general land use was set at 8 (disturbed fill, <br /> topsoiled, no rock cover); for the undisturbed condition the general land use was set at 6 <br /> (range, semi-arid with coarse soils). <br /> LS factor values were calculated in RUSLE by entering slope length and gradient <br /> percentage for the slope segment(s) in each reclamation unit. Additional input information <br /> required by RUSLE included soil texture= loamy sand. <br /> Table 1: Reclaimed Unit Slope Characteristics <br /> Cross- <br /> Elevation Section <br /> Cross- Elevation Change Length Slope LS Factor LS Factor <br /> Section (Ft) (Ft) (Ft) (%) (Reclaimed) (Undisturbed) <br /> A-A' 4825-4805 20 796 2.51% 0.654 0.388 <br /> SL-12 3 May 2024 <br />