The Northwest Territories Power Corporation (NTPC) says the Taltson Hydro facility in Fort Smith, Canada, will remain offline until early December as remediation work continues on the station’s surge tank.
A corrosion issue discovered earlier this summer has kept Taltson out of service since early August. NTPC confirmed it has identified a remediation plan that will allow the unit to return to operation once repairs are complete and commissioning is finished.
The work is expected to take about nine weeks, followed by a one-week commissioning period. During that time, South Slave communities will remain on diesel generation.
The surge tank was previously inspected by NTPC engineers in 2013, by a third-party structural engineer in 2015, and by drone in 2023. The 2023 drone mapping showed limited deterioration compared to 2015. A scheduled 2020 inspection using non-destructive testing was deferred and eventually completed in July 2025. Results from that testing showed more severe corrosion than anticipated.
Although surge tank remediation was not part of the Taltson overhaul scope, NTPC had identified it as a future capital requirement in its five-year plan. The current remediation is estimated to cost approximately $15 million, including about $5.2 million in fuel costs for temporary diesel generation.
NTPC stated that if remediation were not undertaken, the South Slave system would remain on diesel for up to two years while a new tank is engineered and installed – an approach expected to cost around $80 million in fuel and operational expenses.
“This remediation project is the first step in a broader, long-term project to replace the surge tank,” NTPC said.
A second phase, now in early planning, involves complete replacement of the tank. The current concept places a new surge tank upstream of the existing one, fabricated in sections offsite and welded together onsite. The replacement is expected to proceed in parallel with the planned Taltson substation project, allowing for shared costs and reduced downtime.
According to NTPC, the selected approach – remediation now, replacement later – represents the lowest-cost option and “ensures safe operation, returns the South Slave to hydro generation earlier, reduces greenhouse gas emissions and reduces hydro downtime when the second phase of the project runs parallel with the scheduled substation replacement.”
NTPC has notified the Public Utilities Board (PUB) that it will apply for a Project Permit for the remediation, as required for capital projects exceeding $5 million.
While the hydro plant remains offline, NTPC is increasing system reliability through additional diesel generation capacity, system coordination improvements, temporary generation rentals, and vegetation management.
Two rental generators are being deployed in Fort Smith (one already online), and Fort Resolution has received an additional rental unit. In Hay River, the largest generator was returned to service in August following overhaul, and two rental units will remain until hydro generation resumes.
NTPC has also added operational staff to support ongoing maintenance and monitoring at both community diesel plants and the Taltson site. Additional vegetation clearing is underway along the transmission right-of-way to mitigate fault risk from trees weakened by wildfire or drought once the line is re-energized.
NTPC is a wholly owned subsidiary of NT Hydro, which is owned by the Government of the Northwest Territories.
Frequently asked questions
-
What is a surge tank
A surge tank is a vital component of a hydroelectric facility that regulates pressure fluctuations and provides a water reserve. It helps to mitigate the effects of pressure surges caused by sudden changes in water flow, especially during startup, shutdown, or load changes, enhancing the overall stability and efficiency of the system.
