2015-09-09_PERMIT FILE - C1981019A ‎(16)‎

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 9/9/2015
• Section_Exhibit Name: Exhibit 07 Methodologies & Assumptions for Sedimentation Pond Design Evaluations
• Media Type: D
• Archive: Yes

2.5 PRACTICE FACTOR, P
The practice factor is used to account for conservation practices for the watershed. The following values
are utilized in the pond design evaluations (Renard et al, 1996) (Schwab and Warner, 1987):
TABLE 4
PRACTICE FACTOR
SURFACE
SURFACE TYPE
PRACTICE
CONTROL
FACTOR
Undisturbed
Mountain Shrub
None
0.90
Oak -Aspen
None
0.90
Sagebrush (good)
None
0.90
Sagebrush (fair)
None
0.90
Disturbed
Topsoil Stripped
None
0.90
Reclaimed
Topsoiled and Seeded
Contour Furrowed
0.38
1 to 2 Year Growth
Contour Furrowed
0.38
3+ Year Growth
Contour Furrowed
0.38
2.6 SEDIMENT PARTICLE DISTRIBUTION
A general sediment size consist was developed based on the weighted average of physical analysis data
results for mine areas. The following grain size components were agreed upon between the DRMS and
Colowyo:
Sand
27 percent
Silt
40 percent
Clay
33 percent
As input into the SEDCAD Model, the grains size curve is as follows:
Finer than 4.75 mm
100%
0.075 mm
73%
0.040 mm
33%
0.001 mm
20%
A sediment distribution was generated from the general size consist, as noted above, and input to the
SEDCAD4 program. The resulting sediment distribution is shown on the SEDCAD4 printouts.
3.0 POND GEOMETRY INPUT PARAMETERS
Pond dimensions and input parameters are obtained from scaled drawings generated from pond as -built
surveys. The input parameters are shown on the SEDCAD4 printouts and summarized in Table 6.
4.0 POND CLASSIFICATIONS AND SPILLWAY EVALUATIONS
In order to address compliance with applicable provisions of Rules 4.05.9(2)(d), 4.05.9(2)(e), and
4.05.9(10), WWC completed an impoundment hazard analysis for all ponds to determine the hazard
classification for each pond in accordance with the guidance provided by USDA- Soil Conservation
Service Technical Release TR -60, "Earth Dams and Reservoirs ". As part of the pond hazard analysis, the
adequacies of emergency spillway structures to meet applicable TR -60 discharge criteria and to maintain
adequate freeboard to prevent overtopping were also evaluated. The TR -60 discharge criteria used in the
emergency spillway capacity and freeboard evaluations are as follows:
Exhibit 7 Page 7 Revision Date: 3/18/13
Revision No.: TR -95