Great
Slave Lake: Pristine…or Polluted?
Great
Slave Water Quality: Filling in
the Blanks
While pollution problems related
to the Great Slave mining industry
would appear to be limited to
the Yellowknife area, water scientists
point out that little is known
about the overall water quality
of northern bodies of water such
as Great Slave Lake. Detailed
information about northern Canadian
lakes ranges from limited to non-existent,
with no data on the effects of
local or global pollution on fish
and other aquatic life. As part
of a recently-launched Canadian
federal research mission, known
as the Northern Rivers
Ecosystems Initiative
(in response to the recommendations
of the Northern River Basins Study),
the fish populations of Great
Slave Lake and the Slave River
are being assessed, and the presence
and abundance of contaminants
in Slave River fish and delta
sediments are being investigated.
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With its remote northern location, vast
area of 28,568 square kilometres, small
population of less than 20,000 people, and
only a handful of heavy industries, Great
Slave Lake is regarded as one of the most
pristine water bodies in the world. Yet
residents of Yellowknife, on Great Slave’s
northern shore, cannot drink the lakewater.
It has been polluted by the area’s
mining industry, forcing the community to
draw its drinking water from the Yellowknife
River, 5 kilometres away from the city.
Arsenic Atmosphere:
For several years, beginning in 1943, the
“roasting” process that was
used to remove gold from arsenopyrite rock
sent arsenic trioxide and sulphur dioxide
into the air. Pollution control devices
installed during the 1950’s trapped
arsenic dust, but arsenic contamination
detected in Yellowknife drinking water during
the 1970’s resulted in the movement
of the domestic water supply intake from
Great Slave Lake to the Yellowknife River.
The gold roasting process at the city’s
Giant gold mine was discontinued in 1999,
leaving 238,000 tonnes of highly toxic,
water soluble arsenic trioxide dust, stored
in 15 underground chambers a few hundred
metres from Great Slave Lake. Although the
storage vaults are contained in bedrock
and sealed with concrete bulkheads, concerns
remain about leaching of arsenic into groundwater.
Surface water contamination from the Giant
Mine’s tailing ponds may also pose
a pollution problem.
Remediation:
A joint long-term management strategy for
the underground arsenic vaults is being
formulated by the Canadian federal government
and the current owner of the Giant Mine;
options include freezing the arsenic in
place, or extracting it and treating it
as hazardous waste.
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