Vancouver sewer mystery: Why did a pipe that was supposed to last 100 years burst after 26?

The good news is work on a broken sewer main that has throttled traffic on one of Vancouver's busiest roadways is winding down for the time being.

The bad news is the burst pipe under Terminal Avenue between Main and Quebec streets remains unfixed, with more work scheduled for the fall.

"There's some longer term repairs to come," said City of Vancouver general manager of engineering Lon LaClaire. 

The pipe was supposed to have a lifespan of 100 years but burst after only 26. LaClaire said whatever caused the problem remains a mystery. 

"These pipes are really designed to not fail," he said. "That's actually been a major component of the delay in all of this work because when it erupted last June, we were scrambling [because] that sewer can't be turned off. It actually has to keep moving."

A bypass sewer line has now been installed to deal temporarily with the break. For a time, pumper trucks had to work around the clock to prevent sewage from spilling into False Creek or coming in contact with the public.

Repairs so far have cost $7.1 million. No official estimate of the final price tag has been released, but LaClaire figures the remainder of the work won't cost a "huge amount."

He said the burst Terminal Avenue pipe — known in sewer engineering parlance as a "force main" —  is identical to the one that broke in Olympic Village last June, flooding the neighbourhood with raw sewage. 

Force main pipes are specially designed to pump sewage uphill.

Crews are still trying to determine why the Terminal Avenue pipe burst. As for whether 100-year pipes come with a warranty, LaClaire isn't sure.

"That's a good question," he said.

"There's a very small segment of our sewer system that involves force mains and an even smaller set which has this type [of pipe]. But we are very much looking at other locations to know if what happened here could happen again under similar conditions."