2008-12-04_PERMIT FILE - C1994082A ‎(4)‎

• Permit No: C1994082A
• IBM Index Class Name: Permit File
• Doc Date: 12/4/2008
• Doc Name: Drainage and Sediment Control Plan
• Section_Exhibit Name: Tab 13 Attachment 13-12
• Media Type: D
• Archive: Yes

February 1999 Yoart [b7ine * 13-12 Drainage and Sediment Control Plan • 15
Mine Stock Pond Stability Analysis) by iVIWH (2003), 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:1V
• Height from Spillway Invert to Upstream Slope Toe: 5 Feet
The embankments are constructed 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: ~ = 38°; cohesion = 0 psi
• Unit Weight = 120 pcf
Based on these assumptions, a safety factor of 1.56 was calculated by the limit equilibrium analysis. Rule
4.05.9(8)(b) states that stock ponds shall have a min;mtumi 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.
9.0 REFERENCES
Barfield, Warner, & Haan (1981). Applied Hydrology and Sedimentology for Di~•turbedArea~-. Oklahoma Technical
Press, Stillwater, Oklahoma.
Colbond Inc., Product Specification Information, Enka, North Carolina 28728, www.colbond-usa.com
Erosion Control Technical Council, 2006. Standard Speczfication.r for Rolled Erosion Control Product~•, St. Paul,
Minnesota 55118, www.ectc.org
ESCO Associates, Inc., 1993. 1990/1992 Vegetation Baseline Report, Yoast Study Area, Routt
County Colorado. Prepared for Peabody Western Coal Company. (see Tab 10, Vegetation)
Greenfix America, Product Specification Information, Brawley, California 92227, www.greenfix.com
Montgomery Watson Harza (MWH), 2003. Seneca II Mine Stock Pond Stability Analysis (see
Seneca II Mine and Reclamation Plan, Tab 13, Appendix 13-9A), dated August 8, 2003
Natural Resources Conservation Service, 2007. RouttAtea, Colorado, Parts ofRio Blanco and Routt
Counties. Web Soil Survey 2.0 National Cooperative Soil Survey. U.S. Department of
Agriculture, http://websoilsurvey.nres.usda.gov, accessed 12/31/07
Montgomery [~atran Mining Grnup * 16S S. Union Boulevard Suite 460 * I..akett~oat~ Colorado 80228 * [phone]
'x_37 Revised 08/08