2009-03-02_PERMIT FILE - C1980004 ‎(6)‎

• Permit No: C1980004
• IBM Index Class Name: Permit File
• Doc Date: 3/2/2009
• Section_Exhibit Name: Appendix S Sediment Pond Seepage and Stability Analysis
• Media Type: D
• Archive: No

APPENDIX S
McClane Canyon Mine
Sediment Pond Seepage and Stability Analysis
The following stability analysis was conducted to demonstrate the sediment pond
embankment to be in compliance with DRMS Rule 4.05.9(8)(b), `any impoundment not
meeting the size or other criteria of 30 CFR 77.216(a), and located where failure would
not be expected to cause loss of life or serious property damage, shall have a minimum
static safety factor of 1.3 for a normal pool with steady state seepage saturation
conditions'.
The McClane Canyon Sediment pond is located south of the Office Complex and south
and west of the proposed topsoil stockpile. The sediment pond is a dugout pond, thus,
in reality there is only a 2' embankment. In order to most accurately estimate material
properties for the modeling software, the material properties used are based on the
drilling that was performed by Buckhorn Geotech in the fall of 2007. As can be seen on
the following schematics, it is assumed the foundation ends at the bottom of the pond,
and that is where the embankment begins. The summary of material properties used for
the model (description below) is the best estimate with the given laboratory information
and design constraints.
Laboratory data was only gathered on a handful of samples, so in order to get the most
accurate estimate, the drill log and material description for BH#06 (drill hole closest to
the sediment pond) was compared to the laboratory data. For BH#06, from
approximately the surface to 10' Buckhorn described the material as a silty fine sand
which correlates well to the laboratory data generated for BH#01; yielding a unit weight
-' of 109.5 pcf. Drill Hole BH#06, from a depth of 10-22' was described as a yellowy brown
clayey silt, which correlates well to laboratory data for BH#02 and yields a unit weight of
114.2cf. Cohesion for both layers was an estimated conservative value of 100psf.
Stabifit Anal sis Material Pro ernes
I
Saturated Angle of
~.
Hydraulic Internal Unit

T Conductive Friction Cohesion Weig ht

,...._
~. Material i

Embankment
Foundation ~-~ ~
~
~
--
..~ (ftlsec)

1 (10-4)
1 (10-4) (degrees) ~

30
30 _
~ (psf) ~ (pcf)
_J
100 f 110
.100 ~ 1 4
m. ~...-....
...____~_,.
~~

~.-...

~~
The seepage model shows the phreatic surface crossing the embankment and
discharging into either McClane Creek or E. Salt Creek. The calculated phreatic surface
was used in each of the stability analyses. Because of the location of the pond, and it
not being a true 'dam', two embankments were analyzed for completeness. (1) stability
of 2' embankment on the northwest side of the pond near McClane Creek, and (2)
analysis of the 2' embankment on the southwest side of the pond near E. Salt Creek. In
each case, the stability exceeds the minimum factor of safety of 1.3 for a normal pool
with steady state seepage and is therefore in compliance with Rule 4.05.9(8)(b).