Calgary crews focus on problem 'hot spots' after critical water pipes arrive from San Diego

Two key pieces of pipe needed to complete repairs to a water feeder main that suffered a catastrophic failure, triggering ongoing local water restrictions, arrived in Calgary from San Diego, Calif., Tuesday night, and are now being prepped for installation.

During the city's Wednesday morning briefing, Mayor Jyoti Gondek thanked the southern California county's water authority, saying a local shop is in the process of sandblasting the pipe and coating it with epoxy to ensure it's ready to go as crews set to work on five "hot spots" along the main that need fixing.

"As we heard yesterday, these hot spots are not leaks, they are sections of the feeder main that needed an immediate repair," Gondek said.

Wednesday marks two weeks since the Bearspaw south feeder main — which is 11 kilometres long and as wide as two metres in parts — suffered a rupture. Since then, Stage 4 water restrictions on outdoor water use were enacted alongside a citywide fire ban.

Responding to questions about why the infrastructure was brought in from San Diego as opposed to it being sourced from somewhere closer, Gondek said the city did consider local options first, but the size of the pipe posed a significant challenge.

"This is not generally the size of pipe that is used in oil and gas operations," she said.

"Generally, if this type of a part is available, it's because an organization that provides water to residents is the one that has it on hand. And that's why the San Diego County Water Authority has been such an important partner for us."

Gondek says the city chose the option that would make repairs faster. 

All of this has put a spotlight on water infrastructure, and one expert says the rupture might have something to do with what the water feeder main is made of.

Graham Bell is a research associate professor with the department of Civil and Environmental Engineering at the University of Tennessee. He's also the vice-president of technical services for Structural Technologies, which specializes in the repair of large diameter pipe.

In an interview with CBC Radio's The Current on Tuesday, Bell explained the Bearspaw south feeder main is a prestressed concrete cylinder pipe (PCCP), which is a composite pipe material made primarily out of concrete.

"Most of our pipes were made of a single material, like cast iron, or steel, or maybe slightly reinforced concrete up until about World War II when we needed steel for the war effort," said Bell. 

To explain the layers of this PCCP, he says concrete is first cast with a thin steel cylinder inside of it, and that steel cylinder exists as a membrane to keep the water inside the the pipe. Then, it's wrapped with incredibly high-strength steel wires, which Bell says is "about four to five times stronger than the steel can that's on the inside of it."

It's those steel wires that determine the structural capacity of the pipe.