ENFORCE30153

• Permit No: M1988112
• IBM Index Class Name: Enforcement
• Doc Date: 4/21/1992
• Doc Name: POTENTIAL SEEPAGE THROUGH THE TAILINGS IMPOUNDMENT LINER AT SAN LOUIS PROJECT
• From: MLRD
• To: BRUCE HUMPHRIES
• Media Type: D
• Archive: No

iii iiiiiiiiiiiu iii •
STAT~F
MINED LAND RECLAMATION DIVISION
Department of Natural Resources
1313 Sherman St.. Room 215
Denver. CO 60203
303 866-3567
FAx~ 303 8328106
DATE: April 21, 1992
T0: Bruce Humphries /~
FROM: Allen Sorenson
OF CDf
ti~~ ~-;
.~=
~y .
Roy Ramer.
Governor
M2hael B Long.
Drv~s~on Drtc ctor
RE: Potential Seepage Through the Tailings Impoundment Liner aJt the
San Louis Project
Potential leakage through the VLDPE liner could occur through flaws in the
liner, and by permeation through the liner. Unsaturated flow from the base of
the tailings impoundment to the water table will occur when the sp cific
retention of the sub-soils (estimated by SRK to be ten percent) is exceeded.
The imperative question is whether the seepage from the tailings i poundment
will be of a quantity that will raise the moisture content of the ub-soils
beyond the moisture content at which gravity flow through the soil will occur.
One factor upon which the rate of seepage depends is the head applied to the
liner. The sub-drainage layer above the liner is designed to mini ize the
head on the liner. I have asked Rob Dory of SRK to supply the Division with
demonstration of what the maximum head will be, based on the perme bility of
the drainage laver and the amount of water entering it.
I have performed calculations for the rate of seepage (see attache sheet) for
both one and two feet of applied head. The amount of seepage due o
permeation through the liner under a two-foot head is .0061 cu.ft. yr.
per sq.ft. of liner. With 7,300,000 sq.ft. of liner at build out, 'this
results in 44,530 cu.ft./yr. seepage. For one foot applied head, ~he rate of
seepage due to permeation through the liner is .0031 cu.ft./yr. pe sq.ft. of
liner or 22,630 cu.ft./yr. for the impoundment.
The amount of seepage due to flaws in the liner, based on one .1 s~.cm. hole
per acre, is insignificant compared to seepage due to permeation. SRK has
calculated an amount of seepage due to liner flaws, assuming one-f~ot head, to
be 63.4 cu.ft./yr. I have asked Rob Dory of SRK to submit these c lculations
for review. These calculations become very complicated, involving 'some
complex differential equations, so I have as yet not attempted the myself.
These models should involve hems-spherical or conical zones of flo above and
below the liner flaw; this is what should be looked for in the SRK'submittals,