The GREGI research team has conducted, since 1992, a large amount of
characterization and research work on the site of the South waste rock dump at La
Mine Doyon, Quebec. This is part of a larger research program going on at this site
since 1990 and aimed at the understanding and the solving of acid mine drainage
problems associated with waste rock piles. This research program is part of the
MEND national program and is funded by La Mine Doyon (owned by Lac
Minerals and Cambior), by the Quebec provincial government through CRM and
by the federal government through CANMET. This report is submitted to
CANMET as required in the funding agreement.
Acid mine drainage (AMD) generation from waste rock dumps (WRD) constitute a
challenging problem for the mineral industry of Canada. Unlike AMD generated
by tailings ponds, AMD generated by WRD are more concentrated and can reach
much higher flow rates. So, even if acid generating WRD are less common than
acid generating tailings ponds, they constitute an important threat to the
environment and must be managed at great cost by the mineral industry.
La Mine Doyon South waste rock dump is one of the largest acid generating dump
in Eastern Canada. Since the beginning of this research program, numerous reports
describing the site and the ongoing physico-chemical processes had been released
by GREGI. It is now well established that the large magnitude of the AMD
production at the WRD is related to the rapid supply of air and water to the
reaction sites through convection and percolation in this very permeable porous
medium.
Water entering a dump from precipitation is a key element in the AMD generation
processes and is the main vector of acid release into the environment. This is why a
complete characterization of the AMD processes in a waste rock dump must
include a comprehensive water budget.
The first objective of this report is to present the hydrologic data made available by
the various characterization programs going on at La Mine Doyon. This data is
growing as monitoring continues and as new monitoring devices are regularly
added. This report presents a preliminary analysis of a developing body of data and
knowledge about hydrologic processes at La Mine Doyon South dump.
The measurement of hydrologic variables like rainfall, temperature and drainage
flow rates is straightforward. But other key hydrologic variables, like infiltration,
are more difficult to measure and some development of monitoring procedure or
devices are included in the project. Automation of monitoring devices is also used
to ease the task of on-site data collection and ensure a more continuous record of
key data. The second objective of this report is to present both classical and
innovative methodologies for monitoring hydrological processes at La Mine
Doyon site.
The third and final objective of this report is to present a comprehensive water
budget of the South dump. This budget must be consistent with observations
provided by the geochemical and mineralogical data available. This type of
information was used to build a geochemical mass budget related to the water
budget through concentration and volume changes.
As stated earlier, classical hydrological methods were used when applicable. These
include analysis of meteorological and climatic data from close by weather stations
as well as the operation of an automatic weather station on the site. Weir stations
and piezometers are also operated on the site. Some less standard instrumentation
used in this project include lysimeters stations.
The methodology is thus straightforward. We try to measure as many hydrological
variables as possible to obtain the longest and most accurate records as possible.
This data is used to build the water budget. As the project has been going on for
more than 4 years, some records are becoming more and more significant.
Moreover, as the water budget picture becomes clearer, data deficiencies are
identified and new monitoring devices are designed and put into operation.
The analysis of hydrological data collected is also supported with some modeling.
Models are used to assess hydrologic variables that cannot be measured. Model
calibration with measured data ensures genuine modeling estimations.
