More answers and more questions brought on by investigation into Calgary's catastrophic feeder main break

Months after one of Calgary's treated water arteries burst this summer, a 600-page report into what caused the break was finally presented to city council on Wednesday.

The third-party review points to several failure mechanisms, including microcracks along the pipe and surrounding soil conditions, which contributed to the deterioration of the feeder main and its ultimate rupture. 

Built in 1975, the Bearspaw south feeder main, which is 11-kilometres long and as wide as two metres in diameter in parts, is an integral part of Calgary's civic water system. It transports roughly 60 per cent of the city's treated water supply.

When the Bearspaw south feeder main broke on June 5, it prompted a local state of emergency, threatened the city's potable water supply and led to various levels of water restrictions for Calgary and surrounding communities for months afterward. 

While the initial break took weeks to fix, with emergency parts arriving from as far away as San Diego, the crisis also unveiled chronic issues with the pipe itself. This led to several other hot spots being identified as in need of urgent repairs. 

Soon after the break, the city ordered a consultant t review of what led to the deterioration and ultimate failure of the pipe.

The investigation — which was overseen by Associated Engineering — concluded that several factors contributed to the pipe's catastrophic failure, as well as stress at five hot spots, including:

• Microcracking along the protective mortar outer layer of the pipe, which allowed soil contact with the prestress wires. Based on the investigation, it appears the feeder main could have experienced previous damage to the outer layer of the pipe, according to the city.
• High chloride levels in the soil at various locations, as well as within certain portions of the mortar that had already experienced microcracking. 
• Severe damage to the wires that keep the pipe strong, including various wires that had snapped following stress corrosion and hydrogen embrittlement. The damage, the report suggests, appears to be caused by chloride penetrating the microcracks along the mortar of the pipe.

Chloride levels became a notable discussion point following Wednesday's presentation.

According to the report, there is "no doubt" chlorides played a role in the distressed pipe portions that were exhumed from the area of 16th Avenue and 42nd Street N.W. 

The city's road salt and brine de-icing formula is highly likely to have contributed to the elevated chloride levels that were found in soil samples.

Steve Wyton, manager of asset management planning with the City of Calgary, says the city plans on investigating the use of road de-icing agents further in order to assess their use. 

"We are going to be increasing our soil monitoring and soil testing program," he said Wednesday. 

"We definitely need to better understand what are the impacts going forward on this specific piece of pipe, but as well to the entire feeder main network."

Wyton added that this same type and vintage of pipe is being used in other parts of Calgary's water system, so assessing the soil in other areas will be necessary.

According to the report, 12.5 per cent of the 9.6 kilometres of pipe that was initially inspected right after the failure was in some form of distress — which is what led to the first round of rehabilitation repairs. 

"These inspections revealed a total of 239 deteriorated pipes in addition to the pipe that ruptured," said Wyton.

"To put this in context, there are over 2,000 pipe segments within the feeder main. So in other words, the majority of the pipe segments are in good condition."

Wyton added there are segments of the feeder that still have minor to moderate structural deterioration, but overall, the pipe is considered to be in fair condition.

The report concluded that the design of the pipe was consistent with accepted guidelines at the time it was constructed, and also that its use and operations were within its design parameters, meaning no drastic pressure changes immediately leading up to the break were responsible for the pipe's failure.

"As engineers, we don't design things to fail as epically as that pipe failed. We design things to show signs of failure slowly," said Kerry Black, University of Calgary assistant professor and Canada Research Chair in the department of civil engineering. 

"What we saw there was a much more brittle failure."

Black says the report does answer a few of the immediate questions about why the pipe failed, and that there isn't necessarily one unexpected element that can be blamed. 

However, she also believes that this report will trigger more discussions around what might be leaching into Calgary's soil.

"I think you're going to see more investigation into the quality and nature of the soils in our city and how that may be contributing long-term to a faster deterioration of our pipes."

Investigation faces criticism

One city councillor says he's not completely satisfied with the investigation.

"We still haven't heard the catalyst," said Raj Dhaliwal following the presentation.

"Given what I heard … there was some technical design information missing. Why didn't we risk rank it appropriately and make it a higher probability of failure?"

The infrastructure and planning committee also heard about how city officials prioritize pipe inspections based on risk. While the feeder main's failure would have a high impact if it failed, it was deemed to be a low risk.

The Ward 5 councillor says this report didn't give him a definitive answer as to how a similar problem can be avoided in the future.

When the city requested that an outside consultant investigate the cause of the feeder main's rupture, at the time, Mayor Jyoti Gondek said a full third-party review would "go a long way to providing both answers and transparency for the public."

On Tuesday, though, Gondek was critical of how the investigation process unfolded.

It's because elements of the investigation were completed by consultants in June and August, but the conclusions weren't released until now.

"We gather all kinds of information, and then we set about the business of writing a report … and until that report is done, we don't hear anything about it. I think that's got to change," she said.

"If there's anything that we've learned this summer, you have to get information out to people as you know it, and hanging on to things until we have a report to submit is a habit that we're going to have to break."

Gondek also continued to press the report's presenters from city administration during Wednesday's council committee meeting on why updates about what caused the break weren't shared with the public as they were discovered.

"It is great to have a comprehensive report like this, but I've said this before: there are components of this report that could have been released publicly much sooner than they were," she told reporters at city hall on Wednesday, following the presentation of the report.

Finalized costs still TBD

The final cost of the 29 repairs to the pipe, including the repair of the original break, is still being finalized.

Early estimates suggest the initial repair and first five hot spots will cost $20-$25 million, while the subsequent repairs could cost $15-$20 million.