1983-10-20_HYDROLOGY - M1977378

• Permit No: M1977378
• IBM Index Class Name: HYDROLOGY
• Doc Date: 10/20/1983
• Doc Name: Seepage Control Program
• From: MLRD
• To: Standard Metals
• Permit Index Doc Type: Hydrology Report
• Media Type: D
• Archive: No

OF COO /
NQ p DEPARTMENT OF NATURAL RESOURCES i;11--�y77
David H.Getches,Executive Director -_31U
, 8 MINED LAND RECLAMATION DIVISION
�—� D"ID C.SHELTON Director
Richard D.Lamm
Governor
TO: /ark Loye
FROM: Mic 1 Stanton
RE: Standard Metals Seepage Control Plan
DATE: &/ October 20, 1983
The seepage control program implemented by Standard Metals was apparently
planned to dress�Fe-visual seeps occurring at the toe of the
impoundment and to reduce phreatic levels within the embankment.
An interesting paradox exists between the construction of this pond and
the Board's stipulation regarding the ground water conditions. This
facility was designed to be a free-draining structure. The company 's
correspondence indicates that impoundment was constructed over alluvium
and that a blanket drain (sized from the upper portion of the alluvium)
extends approximately 100 feet beneath the dam. The dam was formerly
constructed using the centerline method of construction; tailings are
cycloned to produce a sands fraction for the dam, and slimes are then
discharged to the pond. This method of dam construction is often used
where space prohibits downstream expansion of an embankment. Tailings
deposition thus alternates between the upstream and downstream methods
and the dam consists of intertongued sands and slimes. Saturation of the
materials in the dam is cause for concern regarding the embankment's
stability; it is thus important that the phreatic level in the dam be
kept as low as possible. Hence, the relationship between the geology,
the stream, and the design of the facility has probably permitted
communion between solution in the pond and the Animas River.
A proposed change in tailings deposition from the centerline method to
the upstream method will place more material over saturated slimes. This
proposal carrries with it concerns regarding the structural integrity of
the embankment. Such plan should be carefully monitored and probably
should not continue for a prolonged period in which a substantial load
would accumulate over the underlying slimes fraction.
The corrective measures instituted by Standard Metals will control some
of this seepage, but will probably not eliminate it. Because of the
alluvium underlying the pond, it would be reasonable to assume that some
ground water flow exists between the pond and the river, this situation
may also exist with the blanket drain. The only way to potentially
eliminate seepage would be to line the pond or construct a grout-type
cutoff curtain and corresponding pump-back system. However, both such
measures may be impractical at this site.
423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. [phone]