2008-01-16_PERMIT FILE - C1994082A ‎(6)‎

• Permit No: C1994082A
• IBM Index Class Name: Permit File
• Doc Date: 1/16/2008
• Doc Name: Drainage and Sediment Control Plan
• Section_Exhibit Name: Tab 13 Attachment 13-12
• Media Type: D
• Archive: Yes

Febrnrny 1 JJJ Yoart Mine * 13-12 Drainage and Sediment Control Plan •3
given area. Curve numbers were assumed based on site-specific vegetation and soils information. Where no
vegetation or soils data were available, average conditions were assumed. Where multiple conditions existed within the
watershed, an area-weighted trove number was calculated. A summary of the curve numbers used for this
evaluation is presented in Table 13-12.1, Toast Mine Cuuve N~-unber.
TABLE 13-12.1
YOAST MINE 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% - 70% C 63
Fair (30% - 70% D 70
Mesic Draina e Fair 30% - 70% C 81
Herbaceous Good >70% D 85
Herbaceous Good (>70%) C 74
Rock Outcrop Bare D 98
Disturbed Pit & Pre-Stri ed Bare C 91
Spoil Bare C 86
Haul Road Bare C 91
Reclaimed Fair (30% - 70%) B 71
. 3. (1 S ~ D I MIJ NTATION 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 sedunent yield using the Revised Universal Soil Loss Equation (RUBLE). The input
parameters used in the sedimentation analyses are presented in die following sections.
3.1 RAINFALL FACTOR, R
;1 rainfall factor of 30 was used for the original 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 utilize a rainfall factor of 10.
3.2 SOIL ERODIBILITY FACTOR, K
The soil erodibility factors For the subject site were determined based on soil survey information (Nyenhuis,
1997). The values are shown on Table 13-12.2, Soil Erodibiliry Factor (Soil Conservation Service, 1983).
3.j L[il~'GT'1-F-SLOI'r FACTOR, LS
Input parameters to determine the LS factor were obtained from permit maps of the watershed areas.
\Tahies measured from the permit maps are presented in the attached SEDCAD4 results.
tl~lartgorrrery IYatsnn 11 fining Grarp * 165 S. Union Bonlevarrl, Suite 460 * Luke:vood, CoAoando 80278 * [phone]
'TR-3G Revised 08/07