The City of Yellowknife says water supply returned to normal on Monday afternoon following four days of drawing water from Yellowknife Bay.
Ordinarily, the city’s water is drawn from the Yellowknife River – using an 8.5-km underwater pipe – to avoid taking water from the bay because of concern about Giant Mine, the bayside contaminated site of a former gold mine.
On Thursday last week, the city advised environmental regulators of an emergency switch in water source because of a failure between the Yellowknife River pumphouse and the water treatment plant.
The city sent divers to inspect the pipe but only uncovered the issue on Monday afternoon.
Chris Greencorn, the city’s director of public works, told Cabin Radio a series of recent power outages had contributed to “a perfect storm of events.”
“Our public works crews worked in conjunction with Yellowknife divers on short notice to complete underwater inspections,” Greencorn wrote on Monday after supply from the river had been restored.
“After an extensive investigation … we determined the cause to be a combination of electronics failure and multiple on/off cycling of the water treatment plant due to intermittent power supply on September 11, 2022.”
Greencorn said the outages that day – there were at least six in a 24-hour span – caused more vibration in the city’s system than normal.
“The vibrations that occurred mobilized pipe sediment that clogged some components, that impacted pumping operations,” he wrote.
“This was confirmed by the dive team, that noted some areas of the underwater line had sediment freed from around the pipe, indicating movement.”
Why the river is preferred
The city is spending more than $30 million, much of it federal cash, to replace the ageing river pipeline and preserve the river as its water source. A 2018 report concluded that piping water from the river is much more expensive than doing so from the nearby bay, but safer.
“Arsenic contamination of the Yellowknife Bay source water due to a major failure at Giant Mine has a low probability of occurring but is considered plausible,” the report stated.
No such failure at Giant Mine has recently occurred and the city says there was no issue with the Yellowknife Bay water used in city homes between Thursday and Monday.
“Preliminary arsenic testing was completed and no detectable levels were noted,” Greencorn wrote in a Thursday email published to the regulatory public registry.
“Based on continuous testing of the bay water,” he continued, “we have no reason to believe that there are any parameters of concern that may impact drinking water quality.”
Bay is ‘pristine’ source, says city
On Friday last week, responding to Greencorn, NWT government water resource officer Meg McCluskie had suggested that the city let residents know about the change.
“There has been significant public concern over the years about the quality of water in Yellowknife Bay. It is advisable that you communicate with the public that, while the current intake location to bring water to the treatment facility has changed, the City of Yellowknife continues to provide its residents with water that meets health standards,” McCluskie wrote.
“We will take that under advisement and determine next steps after a fulsome review of all documents,” Greencorn responded.
“We consider ourselves very fortunate to have two pristine raw water sources at our disposal. And while there has been significant public concern as you note, we have years of water quality data showing the lake water is of high quality, and the concerns are largely due to the presence of Giant Mine.”
Speaking with Cabin Radio on Monday, Greencorn added that the issue demonstrated the need to replace the pipeline, regardless of the cost.
“That thing is 50-some years old,” he said. “This is exactly why we started putting plans in place for a replacement.”
Reporters are due to tour Giant Mine later this week as the federally led remediation project shows off progress to date.
There are more than 200,000 tonnes of a toxic mining byproduct, arsenic trioxide, stored in chambers under the mine. The remediation project has an on-site water treatment plant of its own and has stated water management will be “an important part” of current and future work at Giant.