Cost of Yellowknife's replacement water pipeline balloons again

The estimated cost of replacing a key piece of infrastructure the city of Yellowknife relies on for drinking water has nearly doubled in the span of a year. 

In a report presented to city council on Monday, consulting firm AECOM detailed the estimated costs to replace an aging water pipeline that runs from Yellowknife River to the city.

In 2017 the city hired a consulting firm to evaluate replacing the Yellowknife River pipeline. It estimated the cost to be $34.5 million. In 2024 that was revised to likely cost $62.7 million. Now in the latest report, a new pipeline is estimated to cost $107.7 million. Detailed upgrade designs for pumphouses and replacement of the pipeline are said to be the reason for the price jump.

Yellowknife draws water from Yellowknife River and has used the eight-kilometre pipeline since 1968-69. The city began relying on the river to avoid pumping water from Yellowknife Bay, its previous primary water source, due to concerns around arsenic contamination.

Ryan King, the project lead for AECOM, presented the report to city council members. He said things have changed since the 2017 report, including increased knowledge of Giant Mine rehabilitation program plans.

"There's been a lot of data, a much better plan, a much more known plan, and the timeline is now known from the Giant Mine project remediation and the risks of arsenic," King said.

Arsenic contamination a priority consideration for report

The report also raised two new options for the city to consider. 

The first being that the city continues using the Yellowknife River source with the bay as a backup, then when the pipeline can no longer be used, Yellowknife Bay would become the primary source.

The second new option is that Yellowknife Bay becomes the primary water source with the arsenic treatment system. The existing Yellowknife River pipeline would then become the secondary source and back-up if needed. 

All proposed plans include varying upgrades to the pumphouses.

While switching to Yellowknife Bay water would be cheaper than replacing the pipeline to the river, as it would run a cost of around $60 million, King acknowledged the longstanding concern of arsenic contamination. However, he says this has a low probability of occurring but is considered plausible in the case of a major failure at Giant Mine.

King added that Health Canada estimates that the average Canadian has a 40 per cent risk of developing cancer in their lifetime. He said the calculated incremental risks with drinking water from the bay source increases the value to 40.0044 per cent and for the river it's 40.0019 per cent.

The report states that with more information around risks being available, these could be addressed by the construction of a new water treatment plant and arsenic treatment system. This would treat contaminated water before it is discharged to Yellowknife Bay.

Coun. Ben Hendriksen brought up the question of what exactly could happen in the case of water contamination with the treatment plant.

"How effective is it?" Hendriksen asked.

King replied that there are limits to what it can treat.

"There's a threshold at the concentrations where it'll exceed its treatment effectiveness," King said.

The report states that the risk of a breach resulting in a catastrophic release affecting the bay water source is expected to be reduced when the next phase of the Giant Mine Remediation Project enters service in 2026. 

It adds that risks would be further reduced when the tailings ponds are fully decommissioned and other mine closure activities are completed.

The presentation of the AECOM report took place in advance of a memo that is expected to be presented to city council on March 10 to inform disaster and relief funding allocations.