WC136 MayJune 2024 - Magazine - Page 26
soils to an arsenic concentration of 340 milligrams per kilogram
within areas previously developed for mining, and to an arsenic
concentration of 160 milligrams per kilogram for the townsite,
marina lands, boat launch, and shoreline. As well, contaminated
sediments and historically deposited tailings located in water
along the shoreline will be covered with rock, a new boat launch
will be built, and existing marina infrastructure will be rehabilitated. Contaminated sediment is slated for removal from Baker
Creek, which runs through the mine site to Yellowknife Bay, and
some parts of the creek will be realigned and widened to mitigate
future flooding. Plans for the creek also include construction of
new fish habitat, revegetation to prevent erosion and sediment
loading, and landscaping to manage surface runoff.
Water is also central to the project’s pollution treatment
systems. Currently, water that infiltrates into the underground
mine is pumped to a large surface-level tailings pond for storage
and, during roughly half the year when temperatures are warm
enough, the water is directed to an effluent treatment plant
to reduce concentrations of arsenic and other contaminants.
The treated water then goes into a settling pond followed by a
polishing pond for discharge when it meets the project’s licensed
effluent quality criteria.
However, this setup is temporary. A new water treatment plant
designed to meet federal drinking water quality guidelines of 10
micrograms of arsenic per litre is slated for completion by April
2026. Plato said the new plant will add a clarifier tank to separate
sludge and liquids, sand and anthracite gravity filters to remove
suspended particles, and carbon dioxide to reduce pH and thus
increase adsorption capacity. The plant will have meters to confirm treatment targets are met prior to year-round discharge by
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WATER C AN ADA • M AY/JUNE 2024
pipeline to an outfall in Yellowknife Bay. Sludge waste, meanwhile, will be dewatered using a filter press that reduces solids
to 20 per cent in volume, and the sludge and spent adsorption
media will be disposed in a purpose-built non-hazardous waste
landfill on site.
While work proceeds apace, there are challenges. Runoff from
newly constructed covers for the tailings containment pits is
not expected to immediately reach levels deemed acceptable for
releasing suspended solids and metal concentrations.
“Our planned approach is to capture, hold, and monitor
runoff for a short period of time until it meets the project’s surface water discharge criteria, deeming it acceptable for release,”
Plato said. As well, the new water treatment plant isn’t designed
to treat for chloride or sulphates, both of which occur in high
concentrations deep in the stratified mine water pool.
“Our approach is to conduct operational monitoring at the
intake wells and other deep-water monitors to track changes in
chemistry as water is pumped for treatment,” Plato explained.
When remediation activities conclude, CIRNAC plans to
implement a perpetual care plan to document how the site will
continue to be monitored and managed. Plato said the department needs to determine how future generations who live in the
area, as well as other rights holders and stakeholders, will remain
informed about the site.
Although pollution is finally being addressed, Fred Sangris
expresses a fundamental distrust stemming in part from decades
of impacts and loss and fruitless attempts to seek recourse. While
the destruction of the traditional Dene economy and way of
life weighs heavily, perhaps the broadest impact has been with
respect to water. Even by the late 1940s, governments knew to
some degree that local waterways were unsafe and arranged to
supply some Dene communities with potable water, and various
arrangements continue to this day. The City of Yellowknife conveys water from its treatment plant to Ndilǫ during the summer
through above-ground plastic piping, but during the long north-
WAT E R C A N A D A . N E T
Getty Images
A photo taken from Bush Pilot’s Monument near Yellowknife with Ndilo
First Nation land in the distant far left corner. Ndilo First Nation Chief Fred
Sangris says the pristine places his people used to hunt and fish in have
been poisoned by the Giant gold mine.
