es onse No.                                     Response

        Leachate monitoring was addressed in the DEIS. The leachate collection
system should
        provide rapid, readily obtainable samples of leachate quality. Other
monitoring
        instrumentation could be added to plan of operation or during project
operation if needed.
        However, it is uncommon to have sampling points directly within the
waste mass itself,
        regardless of the waste type. Laboratory tests of scale physical
models could be set up
        using actual project process water, tailings, and environmental conditions.

 331   Piping can be controlled by soil gradation requirements both for the
liner and for the
       underlying subbase soil. In addition, piping would be minimized if
the water pressure on the
       liner were controlled by pumping the leachate collection system. In
a well graded soil with
       a moderate fines content, the resulting soil pore spaces should be
sufficiently small to
       retain even unhydrated (not swollen by water) bentonite particles.
Piping is rare or unusual
       with properly constructed lined landfills. The problem has been observed
with water
       retention dams and conventional tailings dams where high hydraulic
heads and more
       permeable materials are commonly employed.

 332   As noted in response #329, the neutralizing capacity of the tailings
is not totally dependent
       on the addition of carbonate sludges.

 333   Refer to response #329. Monitoring of the pore water within the tailings
mass could be
       performed during operations, but sampling would be difficult. There
would be little
       advantage in this type of sampling because there is access to the
leachate via the leachate
       collection system. The depth of neutralization would be unimportant
assuming sufficient
       acidity was produced to even require neutralization.

 334   Refer to response #329.

 335   The DEIS section on MWDF liner-leachate compatibility (page 113) indicated
high
       concentrations of acidic chemicals could degrade the liner. However,
acid leachate with a
       wide range of dissolved salts should not affect amended soil permeability
significantly.
       Only strongly acidic conditions for extended time periods can cause
such damage. If such
       conditions existed, they would be detectable in the leachate. With
the physical conditions
       of the site, such acidic conditions are not expected.

       The tailings would not be classified as hazardous because it does
not meet the conditions
       imposed by the EPA toxicity test. Wastes such as flyash, coal spoils
material, and several
       other inorganic waste types also have the potential to form acid leachate
but are not
       hazardous wastes.

 336   DEIS page 13 explained how runoff water would move laterally in the
drain layer to the
        recharge enhancement zones thus minimizing seepage into the tailings
mass. DEIS Fig.
        1-17 provided details of the MWDF showing the perimeter vertical
drains. The use of the
        perimeter vertical drains would allow water to seep into the subsoils
without causing
        saturation or erosion of the dike sideslopes. These drainage features
were included in the
        cap redesign in the second feasibility study for the MWDF. This has
advantages for both
        the groundwater modeling of contaminant transport and for reducing
potential surface



      water and saturation effects on the sideslope cover soils.

337   The effect of water in the sideslopes would only cause probl4
      cross-section would become saturated. The dikes would be (
      deepened vertical drain and horizontal drain segments at the
      possibility for slope stability problems.

338   The geomembrane is one of several features that would be b
      features include the cover vegetation, cover soil, drain layel

      The effective duration of the geomembrane in a buried envi
      where it is kept anaerobic and in contact with soil water, ral



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