Alberta’s engineering regulator says it found no evidence of unskilled practice or unprofessional conduct in the City of Calgary’s management of the Bearspaw South water main that burst in June 2024 — but a forensic investigation commissioned by the city noted that the rupture was caused, among other things, by extensive corrosion, chloride contamination, and brittle wire failure in a 1975-era pipe expected to last a century.
The rupture triggered water restrictions in Airdrie and other municipalities across the region, lasting through the summer and into the fall.
According to the City of Airdrie, "The City of Airdrie purchases water from the City of Calgary. The water is treated by the City of Calgary and then travels in supply mains to Airdrie reservoirs. From there, it is pumped through distribution mains to water service pipes and then flows out of the taps in our homes, businesses and out of fire hydrants."
The Association of Professional Engineers and Geoscientists of Alberta (APEGA) released its findings on May 28 following a 10-month practice review into the Bearspaw South water main rupture. APEGA concluded that Calgary had "sound engineering oversight" and was in full compliance with provincial legislation, regulations, and practice standards.
The regulator launched its review on July 22, 2024. The final report was delivered to the city on May 7, 2025. APEGA stated, "If during a practice review unskilled practice or unprofessional conduct were to be suspected or found in engineering or geoscience practices, APEGA would launch a formal investigation." No such concerns were found.
A forensic investigation commissioned by the City of Calgary and conducted by Associated Engineering found the rupture occurred in a 4.9-metre segment of 1950-millimetre prestressed concrete cylinder pipe that forms part of the Bearspaw South Feedermain (BSFM), constructed in 1975.
According to the report’s executive summary, "The cause of the June 5 failure was the breakage of a sufficient number of prestress wires in a pipe segment causing a loss of pressure resisting capability in the pipe… Approximately 200 wires… were observed to have failed."
The report documented severe pitting, corrosion, and brittle fractures in the prestress wires, along with evidence of hydrogen embrittlement and stress corrosion cracking. These were attributed to chloride penetration through microcracks or damaged mortar coatings on the pipe.
Soil testing along the corridor revealed "significantly aggressive soils" in certain areas. The report concluded the pipe’s structural integrity had been compromised over time by environmental exposure.
Associated Engineering found no evidence that the pipe was improperly manufactured when installed. However, the authors noted that "some of these changes may have extended the life of the pipe if they were in place in 1975."
Pump operation, transient pressure events, stray electrical current, and post-construction loading were all ruled out as contributing factors.
APEGA stated that the practice review included a high-level literature review "to provide context on the magnitude and mechanisms of prestressed concrete cylinder pipe (PCCP) failures." The regulator noted, "At the time of installation, in 1974, the feeder main was reportedly expected to have a 100-year service life."
APEGA’s release said, "PCCPs generally fail in the same way, and such failures are common." It also stated, "The conclusions of the City of Calgary’s forensic investigation into the Bearspaw South rupture, which was conducted by Associated Engineering, are consistent with PCCP failures across North America."
APEGA noted, "Preventing a PCCP rupture is not assured, even with monitoring and predictive technologies in place."
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