Third-party modelling shows that Calgary would need a repair on only one section of the Bearspaw water main in the next five years, giving the city time to do more rehabilitation.

Calgary city councillors received a broader update during the Nov. 26 regular meeting of council on the preliminary findings of the Bearspaw water feeder main failure.

To date, however, city officials said there’s “no smoking gun” as to what caused the June 5 rupture. There is some speculation, however, that de-icing material containing chloride may have been a contributing factor.

Francois Bouchart, director of capital priorities and investment, took councillors through a detailed presentation dating back to the initial break but also included information on the type of pipe the City of Calgary has in the ground in that area. It also reiterated the same initial conclusions as the preliminary report delivered earlier this month.

Bouchart said that since the fixes done after the summertime rupture, only two wire snaps have been detected, from the roughly half-million wire wraps around the 7.3 kilometres of pre-cast concrete pipe. Acoustic monitoring of the stretch is ongoing.

“Therefore, we’re comfortable, we’re confident, that the pipe has stabilized as a result of making those repairs,” he said.

Preliminary findings showed that the pipe met specifications at the time, and it was operated well within parameters. The conditions that led to the failure include microcracking of the outer mortar covering, hydrogen embrittlement, corrosion of the supportive wires and soil conditions – including high chloride content.

“Those chloride levels are not uniform along the length of the pipe. They happen in pockets, and those levels are significantly higher than what was measured approximately a decade ago when we did soil samples back 10 years ago,” he said.

“Combined with a pipe that, if exposed to the chlorides, could lead to the corrosion of the wires.”

Based on modelling done since the repairs, Bouchart said their consultants predicted only one additional repair would be needed over the next five years. That would allow them to take a proactive approach to the rehabilitation of the feeder main.

Better update than before: Mayor Gondek

Calgary Mayor Jyoti Gondek quizzed Bouchart and GM of Infrastructure Services, Michael Thompson, on how a specific cause was being narrowed down.

“It sounds like there’s no consistency in what could have caused this, and there’s no direct correlation between the four conditions you’ve given us and the breakage that we saw,” she said.

GM Thompson said they continue to investigate further.

“But to date, there is no smoking gun as to what caused these failures,” he said.

Bouchart later said that it’s not surprising that there’s no specific cause to the feeder main break, thus far.

“I think that just like other experiences that we’ve had with pipe failures, it’s very rare that there’s just one factor that you have to focus on,” he said.

“There are multiple factors, and therefore we’re not surprised that ultimately, the investigation said that at different locations, different factors came into play.”

Outside of city council chambers, Mayor Gondek said she was much happier with the breadth of information provided in this latest update. She was dismayed by the lack of substantive material in the prior update in October.

“They described some of the conditions, including soil conditions and corrosion that led to the failure, and they talked about the fact that there’s no direct correlation between the causes that they found and what ended up happening,” she said.  

“They also verified that the consultants that they worked closely with did not say that they could have or should have done anything differently, so it was a much better report than last time.”

She did expect that some of this information could have been provided sooner. Still, she hopes that the information provides some sense of relief to residents in Bowness and Montgomery.

“The repairs are working, and I want to thank the community again for being so incredibly patient and so understanding while we went about the planned maintenance, as well as when we had to deal with the emergency,” she said.

“So, I think there’s good news today to be shared that we are in really good shape over the next five-year period. It’s anticipated that one more repair might be needed, but nothing more significant than that.”

Bouchart also said that they would be working with the City of Calgary’s mobility unit to see if there are any mitigations that could be used in these areas for de-icing. He cautioned against taking any significant measures before they had all the information necessary.