During the decommissioning of Les Terrains Aurifères (LTA-Barrick-Bousquet) site at
Malartic, the preferred option for the rehabilitation of the acid-generating tailings
impoundment consisted of constructing a composite cover. The cover was set up
during the winter of 1995-1996 and completed in the fall of 1996. The site has been the
subject of a monitoring study, within the frame of NEDEM 2000, for almost three years,
with the involvement of Barrick, the Ministry of Natural Resources of Quebec and
CANMET through the Canada-Quebec agreement on mineral development. A first
report, concerning the construction and the instrumentation of the multi-layer cover
(NEDEM 2.22.4a 1999) is available. Since that time, a new set of monitoring stations
have been installed on the site in order to get a better in situ spatial representation of
the present conditions, particularly in the slopes.

The present report concerns the performance of the cover during the period of 1996 to
1998. The main findings emanating from the present project are that, by capillary
effect, the cover remained practically saturated over a period of three years, on the
slopes as well as on top, and that the reduction of the average tailings oxidation flux
was shown to be 95 % over the three years of observation.

Some zones showed local water contents lower than the design objective, particularly
on the outer slopes having a significant drop in elevation. The performance observed in
hydraulic break test cells indicate, however, that this type of structure would be
effective in cases where supplementary intervention would be necessary in these drier
zones.