According to engineers, the Coxwell Street Trunk Sewer, which carries the sewage of 750,000 Torontonians, has “failed.”

A 60-metre section of the huge sewer, buried about 40 metres beneath Barbara Crescent, just north of Coxwell Avenue and O’Connor Drive, is cracked and chipping.

But Lou Di Gironimo, general manager of Toronto Water, says the big question remains unanswered.

“When will it collapse? Nobody can answer that question,” Di Gironimo told the city’s public works committee yesterday.

The cracks may be many years old. The only way to inspect the sewer is through robots with video and sonar instruments, he said.

“None of that can give us any structural integrity information ... No one can guarantee me how long it’ll last. It could last decades. We don’t know”

It will take 18 months and up to $30 million to build 600 metres of sewer to bypass the cracked part.

The good news is there’s no sign yet the big sewer is leaking sewage outward, or collapsing inward.

Its flow — three times the volume of the Don River in dry weather — is unimpeded, carrying the waste from one-third of the city to the Ashbridge’s Bay sewage treatment plant.