Yellowknife spent weeks drawing much of its water from the nearby bay rather than its usual Yellowknife River pipeline to combat major leaks in the system.
Ordinarily, the city’s water is drawn from the Yellowknife River – using an 8.5-km underwater pipe – in part to avoid the risk of Giant Mine, the bayside site of a former gold mine, contaminating the bay’s water.
The risk of that happening is low. Unless something major fails at Giant Mine, water in Yellowknife Bay is considered safe by the mine remediation team and the municipality. The city has in the past called the bay and river “two pristine sources” of water.
Even so, reports have concluded the Yellowknife River (which is upstream of Giant) should remain the preferred option. The city is planning to replace its ageing pipe to the river to maintain that supply – a project last valued at around $60 million.
But a regulatory filing earlier this month shows the city switched to using the bay for large quantities of drinking water in January and March.
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Chris Greencorn, the city’s director of public works, said two major water line breaks in relatively quick succession were to blame.
“When we experience a break of that nature and subsequent volume loss, what happens is that will deplete the reservoirs faster than we can fill them. We fill from the Yellowknife River via pipeline, and that pipeline is only so big,” he said.
“Even if we had the pumping capacity to pull more, we’re still limited by the diameter of that pipe. So when we lose that much volume, we can’t replenish the reservoirs fast enough. If there’s a major fire at the exact same time as a water break, we’re in trouble.”
When a reservoir drops to a certain level, it triggers an alarm, Greencorn said. If city staff don’t know how long it’ll take to repair a major leak, they switch from the river to the bay to increase the amount of water that can be pumped, as the bay pipeline has a diameter of 24 inches compared to the river pipeline’s 16 inches.
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“We can make and treat water a lot faster,” Greencorn said.
New pipeline will be wider
This isn’t the first time in recent history that the city has switched to the bay as its water source.
The same thing happened for four days in September 2022. That switch was partly triggered by a memorable day in which Yellowknife lost power six times in one afternoon.
Greencorn says the city also switched to the bay as a water source for a time when its new water treatment plant was commissioned in 2015.
He said the bay’s water is tested monthly for arsenic (the main contamination concern) and other parameters, and that testing is stepped up when the city is drawing water from the bay, “just to make sure everything is being done in a safe and controlled manner.”
The amount of water drawn from the bay in January and March was more than 27,000 cubic metres or 27 million litres. Normally, the city would be limited by regulators to just 600 cubic metres over the same period.
“It’s unusual,” said Greencorn of the two major leaks the city faced this winter.
“We usually only get one, maybe two water breaks in a complete year. This year, unfortunately, we had a couple back to back,” he said.
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“It’s ageing infrastructure. We deal with smaller water breaks all winter, we fix anywhere between 80 and 100 service connections. These bigger main breaks are definitely less common – except for 2024.”
What’s also uncommon is the length of time the city took to notify regulators. The city only filed figures showing it had exceeded the cap set out in its water licence in mid-April – apologizing for the delay as it did so.
Greencorn says the plan to build a replacement pipeline to the Yellowknife River should solve the problem of pipe size. (The city plans to swap back to getting water from the bay while that pipe is being constructed.)
He said that pipeline, when it’s built, will be of larger diameter and can bring more water into the treatment plant, plus the city plans to increase its pumping capacity at the same time.
“We won’t be limited by this,” he said, referring to this year’s issue. “It’ll fix the problem.”
