ENFORCE29442

• Permit No: M1988112
• IBM Index Class Name: Enforcement
• Doc Date: 6/24/1992
• Doc Name: POTENTIAL FOR GROUND WATER IMPACTS DUE TO SEEPAGE THROUGH THE COMPOSITE LINEAR UNDERLYING THE SAN LU
• From: MLRD
• To: BRUCE HUMPHRIES
• Media Type: D
• Archive: No

III IIIIIIIIIIIII III ~
STAT~OF
MINED LAND RECLAMATION DIVISION
Department of Natural Resources
t 313 Sherman St., Room 215
Denver, CO 80203
303 866.3567
FAx: [phone]
DATE: June 24, 1992
T0: Bruce Humphries'
FROM: Allen Sorenson~j ,
OF COCO
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~t'L, ~~ v n Z `.a f ary i./ MiOhael R. LOng,
G . Z ~ ~ T r Division Director
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RE: Potential for Ground Water Impacts Due to Seepage Through ~he
Composite Liner Underlying the San Luis Project Tailing Po d,
File No. M-88-112
I have completed my review of the information submitted by Rob Dore of
Steffen, Robetson and Kirsten (SRK) detailing the ca'c;:lations, sup rting
assumptions, and data used in the design of the containment system r the San
Luis Project's Tailings impoundment facility. Items of primary concern to the
Division that are addressed in the SRK memorandum are:
Support for the use of a permeability for "Type 2" borrow material
used in construction of the tailings impoundment sub-drai, age layer
of 5E-04 CM/SEC, and
Methods used in calculating the amount of seepage that may be
expected to escape the tailings impoundment though potent~al flaws
in the VLDPE liner.
There is a great deal of additional information presented in the SRK technical
memorandum but I will confine my comments to these two main points.
The chief factor in limiting seepage through the composite liner, is~the
ability of the sub-drainage layer to minimize the hydrostatic head a~plied to
the liner. The ability to minimize the head applied, is dependent o the
permeability of the drain layer material. The material specified, b~sed on
grain-size distribution for construction of the drain layer (Section 6.2.2,
Technical Specifications, Appendix J, 112 Permit Amendment, Septembe~ 1989) is
a compromise between a material that would provide permeability for rainage,
and a material that would provide filter compatibility with the tail ngs. The
material specified falls within the SM group of the Unified Soil
Classification System. Testing of material installed during construction
indicates that the material placed was within stipulated grain-size
specifications. The SRK technical memorandum states that "Based upo accepted
relationships for particle size for silty sand and gravel and permea iiity,