WC134 JanFeb 2024 - Magazine - Page 22
FEATURE
In the course of the breach, the pond lost all its process water,
and the slurry of tailings and water, along with mud and other
debris flowed uncontrolled into Polley Lake.
controls, enable the ongoing but gradual release of treated water
into adjacent waterways. At the time of the breach, according
to Mount Polley mine records filed with Environment Canada,
pond holdings included 177 tonnes of lead, 326 tonnes of nickel,
18,400 tonnes of copper, and more than 400 tonnes of naturally
occurring arsenic.
In the course of the breach, the pond lost all its process water,
and the slurry of tailings and water, along with mud and other
debris, flowed uncontrolled into Polley Lake, Hazeltine Creek
and Quesnel Lake, causing erosion in some places and lake levels
to rise by up to 1.5 metres. In total, the breach impacted an area
measuring roughly 2.4 square kilometres. The province immediately declared an emergency and issued a pollution abatement order under B.C.’s Environmental Management Act to manage the
discharge, assess environmental impacts, and undertake protective measures. The province and regional health authority issued
a boil-water advisory and other restrictions, Fisheries and Oceans
Canada temporarily closed part of the local salmon fishery, and
extraction was put on hold.
Post-breach assessment
Over the next few years, impact assessments and reviews overlapped with early remediation and restoration. Reviews examined
tailings effluent deposits on land and in waterways, impacts
on creek structures and lake beds, effects on aquatic plant and
animal life, and changes in soil, water, and sediment. A detailed
site investigation by Golder Associates in 2016 concluded that
persistent organic pollutants and heavy metals such as mercury
in the soil, air and surface water were within regulatory levels,
though sediment layers did exceed standards for lead. Vegetation
was found to contain copper and vanadium, and fish samples
had aluminum, copper, and vanadium, but the report deemed
the risks to subsistence and recreational land users, loggers, and
workers on site to be low. Levels of iron, manganese, arsenic,
molybdenum, and sulphate in sampled groundwater exceeded
drinking water standards, but the report dismissed the importance of this, noting a lack of wells drawing groundwater in the
Hazeltine Corridor. And, the tailings were determined to not be
acid generating and thus unlikely to leach metals. The report’s
authors categorized human health risks associated with the tailings’ storage facility embankment breach as “very low.”
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WATER C AN ADA • JANUARY/ FEBRUARY 2024
Remediation and controversy
In 2019, Mount Polley Mining Corporation (MPMC), the
subsidiary of Imperial Metals that operates the mine, submitted a
remediation plan, also drafted by Golder, that served as the final
requirement of the environment ministry’s pollution abatement
order, which was lifted later that year. And the Mount Polley Review Panel, an independent body consisting of three geotechnical
specialists the province convened, concluded the broad categorical environmental impact of the dam breach and tailings spill
was a matter of physical disruption rather than actual chemical
contamination.
The review panel’s conclusions ultimately led to an emphasis
on physical measures such as restoring creek banks, replanting
forests and other local vegetation, and reestablishing fish habitats
and wetlands, rather than repairing the chemistry. The panel’s report also informed the decision to store the slurry in situ in perpetuity in the lower levels of the water strata of both lakes, more
than 100 metres beneath the surface, as opposed to potentially
risky attempts at removal. In a posting on its website, MPMC
said analyses of water, sediment, benthics, and fish determined
that the tailings at the bottom of the lake are chemically and
physically stable, and the best environmental option was deemed
to leave the slurry undisturbed, let natural sediments slowly cover
it, and allow the lakes to continue to recover naturally.
WAT E R C A N A D A . N E T
