PERMFILE69474

• Permit No: C1994082A
• IBM Index Class Name: Permit File
• Doc Date: 9/27/2007
• Doc Name: Drainage and Sediment Control Plan
• Section_Exhibit Name: Tab 13 Attachment 13-12
• Media Type: D
• Archive: Yes

FeGruary 1999 Yaart Mine * 13-12 Drainage and Sediment Contra! P/an 13
given azea. Cutve numbers were assumed based on supplied vegetation and soils infomtaton. Where no vegetation or
. soils data was available, average conditions were assumed. Where multiple conditions existed within the watershed, a
weighted average curve number was assigned. A summary of the curve numbers used Eor this evaluation is presented
in Table 13-12.1, Yoast Mine Curve Number.
TABLE 13-12.1
YOAST MfNE CURVE NUMBER
Area
Condition Cover Type Hydrologic
Condition Hydrologic
Soil Group Curve
Number
Undisturbed As en/Mountain Shrub Good >70% B 30
Good >70% C 41
Good >70% D 48
Sa ebrush Good >70% C 47
GOOd >70% D 55
Fair 30%<x<70°/n C 63
Mesic Draina a Fair 30%<x<70°/n C 81
Herbaceous Good >70% D 85
Herbaceous Good (>70%) C 74
Rock Outcrop Bare D 98
Disturbed Pit &Pre-Stripped
Spoil Bare
Baro C
C 91
86
Haul Road Bare C 91
Reclaimed Fair (30%-70%) B 71
. 3.0 SEDIMENTATION CALCULATIONS
The sediment calculations used to model the Yoast Mine site were performed utilizing the SEDCAD4
Computer Modeling Program developed by Civil Software Design. The SEDCAD4 Computer model
calculates annual sediment yield using the Revised Universal Soil Loss Equation (RUBLE). The input
pazameters used in the sedimentation analyses aze presented in the following sections.
3.1 RAINFALL FACTOR, R
A rainfall factor of 30 was used for sediment pond designs at the Yoast Mine site. This value is suitable
for bare or disturbed land that is easily eroded. In 2006, SCC initiated updates to pond storage
capacity demonstrations to account for the post mine conditions which generate significantly less
sediment than disturbed lands. The updated demonstrations used a rainfall factor of 10.
3.2 Soil Erodibility Factor, K
The soil erodibility factors for [he subject site were determined based on soil survey information (Nyenhuis,
1997). The values are shown on Table 13-12.2, Soil Erodibility Factor (Soil Conservation Service, 1983).

Montgomery Watron Mmrng Group * 165 S. Union B°uleuarrl, Suite 460 * LokcwaaA Colorado 80228 * (303J 763-5140
TR-30 Revised 05/07