The Centre de recherches minérales du Québec (CRM) has undertaken an
experimental research project to determine the effect of flooding the existing
Solbec-Cupra tailings site; the influence of flooding on covering water quality and
porewater quality in the oxidized and nonoxidized tailings was particularly examined.

The experimental research project was achieved through financial assistance from the
MEND program, with a contribution from CAMBIOR. The on-site experimentation was
initiated in the summer of 1989. The first two phases of the project were realized by the
CRM. The third phase was contracted out to MONTERVAL INC. in 1991. The fourth
phase of this program, contracted out to ROCHE LTÉE, Groupe-conseil, involved a
two year monitoring period.

The flooding experimentation consisted in simulating different scenarios “in situ”, using
instrumented basins. A total of five (5) inert plastic cylinders were driven down to
different depths in the tailings, each cylinder being long enough to allow a minimum
water depth of one meter above tailings surface. Each basin was instrumented with
inside single level piezometers to sample porewater: in oxidized and non-oxidized
tailings, organic soil (peat) and in the underlying till.

Three single piezometers were also installed outside (but close to) the basins, and six
others were installed in the center part of the tailings site; the objective of these was to
assess tailings and sub-soil conditions prior to flooding.

The 1992-1993 program (phase IV) was intended at determining the effect of
neutralization of the oxidized layer of tailings prior to flooding, and involved the
installation of a new basin.

The key conclusions drawn from the experimental results are:

• Flooding of tailings under a shallow cover of water inhibits oxidation of acidic
  tailings, and prevents the continuation of the process in non-oxidized tailings.
  The inhibitive effect is progressive, and porewater in oxidized tailings remains
  acid for a certain period of time before reaching a neutral level.
• Neutralization of the oxidized layer of tailings by adding and mixing finely crushed
  limestone prior to flooding had the effect of rapidly stopping the oxidation process
  and raising and maintaining porewater pH to neutral level.
• A downward infiltration of acid porewater from oxidized tailings was induced by
  the water column in the basin. This phenomenon is not anticipated to happen,
  though, from flooding the total pond as a whole.
• Results from monitoring the water cover quality indicate that flooding of tailings
  under one meter of water will improve the quality of tailings pond effluent, and
  eventually to a level complying with MENVIQ mining industry environmental
  guidelines.
• Results from monitoring the water cover quality also indicate that flooding of
  tailings under one meter of water will eventually result in a pond having the same
  water quality as the incoming surface water.
• Based on the overall positive experimental results, and from an environmental
  point of view, flooding of the Solbec-Cupra tailings site appears as the most
  acceptable rehabilitation solution.