PERMFILE134006

• Permit No: C1994082A
• IBM Index Class Name: Permit File
• Doc Date: 4/25/2007
• Doc Name: Drainage and Sediment Control Plan
• Section_Exhibit Name: Tab 13 Attachment 13-12
• Media Type: D
• Archive: Yes

FeGnrory 1999 Yoarf Mrne * 13-12 Drmnage anr(SeAiment ControlP/an t3
given axes. Curve numbers wue assumed based on supplied vegetation and soils information. 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 oEthe curve numbers used for this evaluation is presented
in Table 13-12.1, Yoast Mine Curve Number.
TABLE 13-12.1
YOAST MINE CURVE NUMBER
Area
Condition Cover Type Hydrologic
Condition Hydrologic
Soil Group Curve
Number
Undisturbed As enlMountain Shrub Goad >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% C 63
Mesic Draina a Fair 30%<x<70% C 81
Herbaceous Good >70% D 85
Herbaceous Good (>70%) C 74
Disturbed Pit &Pre-Stripped
Spoil Bare
Bare 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 Softwaze 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 sediment pond design for the Yoast Mine site. A rainfall Factor value of
30 is consistent with bate, or disturbed land that is easily eroded. This factor is consistent with other
recent erosion analyses performed for the Seneca Mine. In 2006, SCC initiated updates to pond storage
capacity demonstrations. The updated demonstrations used a rainfall factor of 10, which is mote
representative of the postmine conditions.
3.2 Soil Erodibility Factor, K
The loll 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 Erodibility Factor (Sod Conservation Service, 1983).
Montgomery ]Y/atron Mining Group * 165 S. Uerr°n Boxleemr~ Saito 460 *I.okeuroor~ CaGrado 80228 * [phone]
TR-32 Revised 04/07