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

Febrnary 7999 Yoart Mine * 13-12 Drainage and Sedmrent ConholP/an 18
The design results are summarized on Figure 13-12.3, Post Mirtittg Channel Designs. As shown on this
• figure, channel sections with shallow slopes oz low flows will be grass-lined. However, channels with steep
slopes and velocities exceeding 5 fps will be armored. The Pader method for steep slopes was used to
estimate rip rap size. Based on our experience, the rock size estimated by Pader is underestimated.
Therefore, we add 3 inches to the rock size required for design purposes.
7.0 TOPSOIL STOCKPILE SAE
A request for a small area exemption (SAE) has been included in this submittal to cover the planned topsofi
stockpiles at the Yoast mine. Runoff from the stockp$es will be controlled by constructing a small
containment berm immediately down-gradient of the pfles. The SAE request is presented in Appendix 13-
12.4, Topsoil Stockpile SAE, of this Attachment.
8.0 STOCK POND DESIGN
The construction of stock ponds is proposed in conjunction with the construction of various
postmine channels. 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 bas 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. Attached are designs for the proposed stock ponds ST-1 and ST-2. 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 tce of the embankment. The combined slope of all the embankments will be less than
SH: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 Summary Table.
YOAST MINE
STOCK POND SPILLWAY SUMMARY
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 leas 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 impoundments, the
constriction material consists of the same general strata, and the extremely conservative inputs
TA-29 ~ Revired6/06
Montgomery Watrox Mining Group * 765 S. Uuion Boulevard, Suite 460 * Lakenrood, Colorado 80228 * [phone]