Investigation into Calgary water feeder main failure shows several causes

Preliminary findings from the City of Calgary's investigation into why its most critical water feeder main ruptured earlier this year show that several different factors may have contributed to its catastrophic failure.

In a news release sent late Friday, the city says preliminary findings show several causes related to the feeder main failure, including:

• Microcracking along the protective mortar outer layer of the pipe.
• High chloride levels in the soil at various locations.
• Snapped wires following corrosion and hydrogen embrittlement.

"The report indicated that there was not one specific factor that led to the failure of the feeder main in June," reads the release.

The pipe investigation is in response to the June rupture of the Bearspaw south feeder main, a break that threatened Calgary's potable water supply and triggered months of citywide water restrictions. 

The purpose of the investigation — which is being overseen by Associated Engineering and Pure Technologies — is to understand what led to the deterioration of the Bearspaw south feeder main and its eventual failure on June 5.

Built in 1975, the 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. 

The preliminary review of the pipe's design and operations confirmed they were consistent with the proper guidelines of the time, the city says, and operations were also "well within the design parameters of the pipe."

Ongoing feeder main work nearing completion

In late August, the city said more urgently needed repairs along the feeder main were identified during a complete analysis of the pipe. 

Two segments of the feeder main — one along Parkdale Blvd N.W. between 26th Street and 27th Street, and the other at the Memorial Drive westbound off-ramp at Crowchild Trail — are still currently being rehabilitated, but construction work is nearly complete, according to Friday's release. 

While options are still being considered for long-term rehabilitation, the city says the feeder main is "responding well" to all of the rehabilitation work that was completed between June and November.

"Through our acoustic monitoring, we have recorded only two wire snaps on the feeder main between October and November," reads a statement from Michael Thompson, the city's general manager of infrastructure services.

"Throughout July and August, there were 23 wire snaps."

City administration is set to share the preliminary findings of the report during city council's regular Nov. 26 meeting. The final pipe investigation report will be presented at the city's Infrastructure and Planning Committee meeting on Dec. 11.