Calgary city council has learned officials are confident the Bearspaw feeder main is stable after a summer full of repairs in response to June’s critical rupture.
However, modelling shows one more repair may be needed in the next five years, according to a presentation from city administration to council on Tuesday.
“This gives us the time that we need to do rehabilitation of our system,” said Francois Bouchart, the city’s director of capital priorities and investment.
Bouchart said work on that rehabilitation plan is ongoing, with consultants examining whether the city should replace the pipe’s lining, or build an entirely new pipe parallel to the current line.
The information came as part of preliminary findings of an investigation into what led to the feeder main’s failure on June 5, which plunged the city into a summer of water restrictions and repairs on 29 weak segments of the line.
According to Bouchart, all the repairs are now complete and only two wire snaps have been detected by acoustic monitoring along 7.5 km of the line. The report noted 23 wire snaps were detected between July and August on just 2.4 km of the pipe.
“I’m really hoping that residents in Bowness and Montgomery have a sense of comfort that the repairs that were done in their communities over the summer and into September have worked,” Calgary Mayor Jyoti Gondek told reporters.
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The preliminary findings showed several factors believed to have contributed to the rupture of the pipe, which carries roughly 60 per cent of Calgary’s water supply.
Those factors include microcracking of the protective plaster outer layer, wires breaking due to corrosion and hydrogen embrittlement, and high chloride levels in the soil surrounding the pipe.
Officials speculated the high chloride levels may be due to materials used for de-icing on city streets.
However, Bouchart noted there is no one “smoking gun” that contributed to the critical rupture of the feeder main.
“There’s multiple factors that come into play and at different locations, one of those factors might play a bigger role in the deterioration of the pipe than in others,” Bouchart said.
Early findings from the review, conducted by Associated Engineering and Pure Technologies, also found the original design of the pipe was consistent with the proper guidelines of the time, and operations of the feeder main were “well within” the design parameters of the pipe.
City administration noted work was underway to do an inspection of the pipe in the fall and winter months of this year, which typically experience lower water demand, prior to the pipe’s failure.
“The news I heard from city administration was their consultants did not indicate that they could have or should have done anything differently,” Gondek said.
However, Gondek said there is speculation the life expectancy of the pipe was wrong as it broke halfway through its 100-year lifespan.
During the presentation to council, Bouchart said 2024 is a “typical” year for water main breaks in Calgary with 162 breaks as of Oct. 31, compared to 200-300 breaks per year.
While most of those breaks have occured on smaller pipes, Bouchart said Calgary has experienced 17 breaks in its “backbone” feeder main system over the last 11 years which don’t always impact service due to redundancy in the system.
Calgary’s feeder main system is comprised of 469 km of pipes ranging in size, and Bouchart noted nearly 40 per cent are younger than 30 years old.
Only 187 km, or three per cent, of the city’s water system is made of the same pipe as the Bearspaw feeder main, Bouchart said.
To provide additional redundancy, Bouchart said the city is advancing two new feeder main projects to the north and south of the Bearspaw Water Treatment Plant.
“Both of those projects were part of our long range plan,” Bouchart said. “What we are doing is accelerating the delivery of that infrastructure, thereby increasing the redundancy within our system.”
The full report into the cause of the Bearspaw feeder main break is expected to be released on Dec. 11, when it is presented to the city’s Infrastructure and Planning Committee.
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