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 YoartlLline * 13-12 Drainage and Sediment Control Plan • 14
7.0 TOPSOIL STOCKPILE SAE
A request for a small area exemption (SAE) has been included in this submittal to cover the planned topsoil
stockpiles at the Yoast mine. Runoff from the stockpiles will be controlled by constructing a small
containment berm immediately down-gradient of the piles. The SAE request is presented in AppendixY 13-
12.4, Topsoil Stockpile SAE.
8.0 STOCK POND DESIGN
The construction of stock ponds is proposed in conjunction with the construction of various postmine
channels. Locations are shown on Exhibit 13-12.1A, Permanent Channel and Pond Watersheds.
Since the stock ponds are relatively small in size and there are no residential or commercial structures or
mining operations immediately below any of the stock ponds, they do not create a threat to public health
and safety or threaten significant environmental health.
SCC has constructed numerous stock ponds (temporary and permanent) in the Seneca II and II-W
reclaimed areas, which continue to function as designed and according to the applicable requirements of
Rule 4.05.9. Designs for the proposed stock ponds ST-1 and ST-2 are presented in Appendix 13-12.5,
Stockpond Emergency Spillway Design SEDCAD Results. A certified as-built of each stock pond will
be submitted following construction.
All stock ponds are located in reclaimed areas and are not primary sediment control structures. They are
relatively small with a storage capacity of not more than two (2) acre-feet and an embankment height no
greater than five (5) feet measured from the invert of the spillway to the upstream toe of the embankment.
The combined slope of all the embankments will be less than 5H:1V with no slopes greater than 2H:1V.
All stock ponds will contain a single open channel spillway designed to safely pass a 25-yr/24-hr
precipitation event. The spillway will be configured to have a minimum of one (1) foot of freeboard.
Riprap requirements were determined using the PADER Method and adding three (3) inches to account for
conservatism. Emergency spillway configurations and riprap size for each stock pond location is presented
in the Table 13-12.8, Stock Pond Spillway Summary.
TABLE° 13=12:8
STOCK POND SPILLWAY SUMiViARY
Pond 25-yr Flow
(cfs) Bottom Width
(ft) Depth of Flow
(ft) Freeboard
(ft) Riprap
Dso
(in)
ST-1. 18.5 10 0.3 1.0 6
ST-2 44.2 10 0.8 1.0 9
The Colorado Office of the State Engineer was contacted regarding jurisdiction for the permanent stock
ponds at the Seneca II Mine Qanuary 2003). According to the Division Engineer and as stated in Section
35-49-107(2) CSR, any dams that are less than five feet high and impound less than two acre-feet of water
would not fall under their jurisdiction.
The Yoast Mine will incorporate the typical stability analysis for all proposed and future stock ponds based
on the worst-case condition experienced and analyzed at the Seneca II Mine. The rationale for using this
approach is based on relatively small size of the impoundment, the construction material consists of the
same general strata, and the extremely conservative inputs used in the analysis.
A Stock Pond Stability Analysis, conducted for the Seneca II Mine (Tab 13, Appendix 13-9A, Seneca II
Montgomery [Y~atron Mining Group * 16S S. Unian Boulevarr~ Suite 460 * Lakewood, Colorado 80228 * [phone]
TR_37 Revised 08/08