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

FeGrnnp~ 1999 Taart Mine * 13-12 Drainage and Sediment Lontro/ Plan ~ 9
used in the analysis.
• A Stock Pond Stability Analysis, conducted for the Seneca II Mine Tab 13, Appendix 13-9A, Yolume
12) by MWH, used aworst-case scenario, which proved to be stable. In summary, the analysis
contains the following:
A force limit equilibrium stability analysis was completed using the Slope/W software
package. A Morgenstern Price analysis was used in conjunction with a search routine to
estimate the lowest safety factor for the embankment. This method satisfies both moment
and force equilibrium of a given analysis.
For the worst-case scenario, embankment geometry with the following characteristics was
used:
• Embankment Crest Width: 5 Feet
• Downstream Slope Height: 9 Feet
• Downstream Slope Angle: 2H:1V
• Upstream Slope Height: 8 Feet
• Upstream Slope Angle: 2H:IV
• Height from Spillway Invert to Upstream Slope Toe: 5 Feet
The embankments are constmcted from spoil material produced during mining, This
material was placed in controlled lifts and compacted. Based on this fact, observations of
the onsite spoil piles, and typical strength values for spoil material, the following strength
properties were assigned to the embankment.
• Spoil: ~ = 38s; cohesion = 0 psi
• Urtit Weight = 120 pcf
Based on these assumptions, a safety factor of 1.56 was calculated by the limit equilibrittm analysis.
Rule 4.03.9(8)(b) states that stock ponds shall have a minimum static safety factor of 1.3. Based on
this analysis and that the Yoast Mine will use the same construction methodology, it is concluded
that the proposed stock pond designs will meet or exceed the minimum safety criteria established
in Rule 4.05.9.
~.0 REFERENCES
Barfield, Wamer, & Haan (1981). Applied Hydsalogy and Sedimentology for Disturbed Areas. Oklahoma
Technical Press, Stillwater, Oklahoma.
Nyenhuis, J. (Dec. 1997). Seneca II W South Expansion Soil Survey.
Renard, K.G., G.R. Foster, G.A. Weesies, D.K. McCool, and D.C. Yoder, coordinators. (1996). Predicting
Soil Erosion by Water: A Guide to Conservation Planning with the Revised Universal Soil Loss
Equation (RUBLE). Agricultural Handbook No, 703. U.S. Department of Agriculture. ~naldrafi7
Schwab and Wamer (1998); SEDCAD4 Design Manual and user's Guide, University of Kentucky,
Biosystems and Agrculrural Engineering Department.
Soil Conservation Service (1983). Soils of Colorado, Lors Factors and Erndibility Hydrologic Groupings.
• Soil Conservation Service (1986). Urban Hydrology jor Small Watersheds (TK-55).
PR-02 Rrvired3/OS
Montgomery lY/ahan Mining Gro>p * 765 S. Union Ban/amrd, ,fnile 460 * llrkeuood, Colorado 80228 * [phone]