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2.5 PRACTICE FACTOR, P <br />The practice factor is used to account for conservation practices for the watershed. The following values <br />were utilized in the pond design evaluations (Renard et al, 1996) (Schwab and Warner, 1987): <br />TABLE 4 <br />PRACTICE FACTOR <br />SURFACE SURFACE TYPE PRACTICE CONTROL <br />FACTOR <br />Undisturbed Mountain Shrub None 0.90 <br /> Oak-Aspen None 0.90 <br /> Sagebrush (good) None 0.90 <br /> Sagebrush (fair) None 0.90 <br />Disturbed Topsoil Stripped None 0.90 <br />Reclaimed Topsoiled and Seeded Contour Furrowed 0.38 <br /> 1 to 2 Year Growth Contour Furrowed 0.38 <br /> 3+ Year Growth Contour Furrowed 0.38 <br />2.6 SEDIMENT PARTICLE DISTRIBUTION <br />A general sediment size consist was developed based on the weighted average of physical analysis data <br />results for mine areas. The following general size consist was agreed upon between the DRMS and <br />Colowyo: <br />Sand 27 percent <br />Silt 40 percent <br />Clay 33 percent <br />A sediment distribution was generated from the general size consist, as noted above, and input to the <br />SEDCAD4 program. The resulting sediment distribution is shown on the SEDCAD4 printouts and <br />illustrated by the attached grain size distribution graph. <br />3.0 POND GEOMETRY INPUT PARAMETERS <br />Pond dimensions and input parameters were obtained from scaled drawings generated from pond as-built <br />surveys. The input parameters are shown on the SEDCAD4 printouts and summarized in Table 6. <br />4.0 POND CLASSIFICATIONS AND SPILLWAY EVALUATIONS <br />In order to address compliance with applicable provisions of Rules 4.05.9(2)(d), 4.05.9(2)(e), and <br />4.05.9(10), WWC completed an impoundment hazard analysis for all ponds to determine the hazard <br />classification for each pond in accordance with the guidance provided by USDA- Soil Conservation <br />Service Technical Release TR-60, "Earth Dams and Reservoirs". As part of the pond hazard analysis, the <br />adequacies of emergency spillway structures to meet applicable TR-60 discharge criteria and to maintain <br />adequate freeboard to prevent overtopping were also evaluated. The TR-60 discharge criteria used in the <br />emergency spillway capacity and freeboard evaluations were as follows: <br />• Discharge flow basis for emergency spillway capacity evaluation (for a Class B pond): <br />• 100-yr, 6-hr peak flow + 0.12 (PMP, 6-hr peak flow - 100-yr, 6-hr peak flow) <br />• Discharge flow basis for impoundment freeboard evaluation (for a Class B pond): <br />• 100-yr, 6-hr peak flow + 0.4 (PMP, 6-hr peak flow - 100-yr, 6-hr peak flow) <br />Exhibit 7 Page 6 Revision Date: 6/19/09 <br />Revision No.: TR-73