1998-01-10_REVISION - M1988112

• Permit No: M1988112
• IBM Index Class Name: Revision
• Doc Date: 1/10/1998
• Doc Name: SAN LUIS PROJECT PERMIT AMENDMENT ADEQUACY RESPONSES M-88-112
• From: STEFFEN ROBERTSON & KIRSTEN
• To: MLRD
• Type & Sequence: AM1
• Media Type: D
• Archive: No

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BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT
CMLRD ADEQUACY LETTER RESPONSES
Page 5 of 28

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10. ~

The data presented in Attachment 1 also demonstrate that no changes
in metal concentrations and acidity have occurred as a result of the
change in processing.
Please commit to achieving 1x10-s cm/sec permeability for the
underlying colluvial material after it has been compacted to 95Y,
maximum Proctor density. It will be necessary to provide verification
to the Division that this permeability has been achieved prior to
installation of the VLDPE.
RESPONSE: Because of the nature of the underlying colluvial materials, it is
nat possible to achieve a uniform 1x106 cm/sec permeability after
the material has been compacted to a 95% maximum Proctor density.
The combination of the low permeability tailings following
deposition, the drainage layer's ability to reduce hydraulic head
on the geosynthetic liner and the function of both the geosynthetic
liner and compacted soils to limit potential seepage eliminates the
potential requirement for a lower permeability of the compacted
subsoil. Seepage potential is discussed in the response to question
11. BMR can achieve and will commit to achieving a 1x10- cm/sec
permeability in the colluvial materials following compaction and to
perform material testing during construction to confirm tihese values.
I1. t Please provide a detailed discussion regarding the potential for a
detection of leakage from the VLDPE 1 finer to the underlying colluvial
materials. A rationale for the placement of the monitoring wells,
including the potential for those wells to intercept i~eakage from
the tailings facility, should be included.
RESPONSE: Potential leakage through the VLDPE liner could occur via two
different pathways; seepage via permeation through the 'liner itself
and through flaws in the liner. Seepage through the liner itself will
be controlled by the thickness of the liner, the head on the liner
and the permeability of the liner. For the VLDPE liner an equivalent
permeability of 1 x 10-11 cm/sec (manufacturer's literature) can be
assumed.
If permeation occurs from the base of the liner, the fluids will not
immediately migrate to the groundwater. The underlying alluvial soils
at the project are unsaturated and at a moisture content
significantly less than the specific retention of the material.
Specific retention is defined as the moisture content above which
gravity flow through the soil will occur. In general, the groundwater
averages about 150-ft below the surface.