_REVISION - M1980244 ‎(24)‎

• Permit No: M1980244
• IBM Index Class Name: Revision
• Doc Name: PSSA Sump Soil Liner Fill
• From: Golder Associates
• To: DMG
• Type & Sequence: AM8
• Media Type: D
• Archive: No

Cripple Creek & Victor Gold Mining CompanyJune 3, 2003
Mr. Phil Bames -2- 003-2203
• 1. If the SLF is a dispersive clay; or
2. The seepage velocities are high (e.g. more than 3 to 4 feet per second).
Dispersion of a clayey soil occurs when ionic conditions within the soil and water cause clay particles
to deflocculate (e.g the soil structure is broken down). Clayey soils with high dispersiviry will
deflocculate in water and erode when exposed to low-velocity water. A clay's susceptibility to
dispersion is related to the presence of cations (sodium, calcium, magnesium, potassium) in the soil
pore water. Generally, the repulsive forces between clay particles, which act to cause deflocculation,
decrease as the concentration of ions increases. One exception is the concentration of sodium ions, in
which the repulsive forces increases with increasing concentration. Typically, in a clay-water system,
the repulsive forces and the tendency toward dispersion increases as the concentration of ions
increases along the series calcium-magnesium-potassium-sodium-lithium (e,g. a clay with a high
sodium is more dispersive than a clay having a high concentration of calcium and little sodium).
A mineralogical analysis of clay soil from Wilson Creek area at CC&V was conducted by Vector
Engineering and presented in a report entitled "Design and Layout Arequa Gulch Facility Cresson
Project" dated June 1992. The results of this analysis found that the clay soil primarily consisted of
montmorillonite with some illite and kaolinite. Clay soils comprised of montmorillonite clays tend to
be more flocculated (less dispersive) in neutral pH water. The SLF for the external pond has the same
parent rock as for the Wilson Creek area (granodiorite); therefore the SLF should be non-dispersive
when exposed to the water from the extemal pond. Site observations are consistent with this
conclusion. Open slopes with dispersive clays typically have deep erosional gulleys or erosion
tunnels. These features are not observed at CC&V.
Ordinary clays with ]ow dispersivity do not erode in the presence of water unless the flow velocity is
relatively high (e.g. more than 3 to 4 feet per second). Golder evaluated the potential seepage velocity
from liner leakage. Liner leakage rates and velocities were calculated assuming a 1 square centimeter
hole in the geomembrane. The 1 square centimeter hole is considered the "standard hole" size used by
the Environmental Protection Agency (EPA) for landfill liners. The seepage velocity was calculated
for a hydraulic head of both 5 and 30 feet. The calculated velocity from a 1 square centimeter hole in
a geomembrane under 5 feet of head would be approximately 0.0003 feet per second. With 30 feet of
head, the calculated velocity is 0.00] feet per second. The calculated seepage velocities are
considerable lower than threshold erosion velocities of 3 to 4 feet per second.
CLOSURE
The assessment conducted by Golder for the PSSA sump has found that the SLF will not be
negatively impacted by hydraulic head on the secondary liner. ht addition, erosion and dispersion
resulting from potential pond leakage will not damage the SLF.
If you have questions regarding this letter, please contact me at [phone].
Sincerely,
COLDER ASSOCIATES INC.
~~
Johtt"F Lupo, Ph.D., P.E.
• ~. Project Manager
C:\Docummb and Sellings\Idufl\LOCa15n[ings\Taryorary lnmma Fil6\OLKCDZ\OWQ203.0100.09025PSSASump.doc Golder ASSOCIateS