Ask Torontoist: Tall, Green, and (Kinda) Smelly




Ask Torontoist: Tall, Green, and (Kinda) Smelly

20100526asktorontoist.JPG Ask Torontoist features questions posed by you, and answered by our elite team of specially trained investigative experts (also known as our staff). Send your questions to

Reader Ross Pryde asks:

What’s the deal with the large green pipes that stick out of the ground at Gerrard Street and Alton Avenue?

Ventilation stacks at Gerrard Street and Alton Avenue. Photo by Joel Charlebois/Torontoist.

The deal is that these are breathing tubes for a community of mole people dwelling beneath Toronto. Don’t bother looking for them, though. Because of G20 security concerns, they’ve been placed in temporary shelters, even further below ground.
We kid! Actually, these snorkel-like green pipes are the ventilation stacks for a complex sewer system known as the Mid Toronto Interceptor (MTI). Buried eighty to ninety feet underground, the MTI runs between High Park and the Ashbridges Bay Treatment Plant. The twelve-foot-tall green stacks are oftentimes paired with a shorter, candy cane–shaped partner. If you could stick your head down one—something Torontoist does not encourage—you would discover a (very smelly) underground chamber complete with sluice gates acting as valves to control sewage flow. The tunnel itself, bored through solid rock, is about as wide as a TTC bus. Beginning in April 2009, Toronto Water began a process of upgrading a number of the MTI sewer chambers.
Because the MTI is an enclosed sewer system, it requires street level venting. The green stacks, fitted with a series of carbon filters, permit the circulation of fresh air into the system and allow for fetid air to exit. Toronto Water told us over the phone that odours emitted from these stacks are minimal. Staff and patrons at a west end eatery beg to differ, though: they claim the stench from a nearby ventilation stack is so offensive, diners have fled in disgust.
Completed in the mid-seventies, the MTI was constructed as a means of preventing untreated sewage in Toronto’s poorly conceived combined sewer system from overflowing during storms. When this occurs, untreated waste ends up in Lake Ontario.
Including the green pipes at Gerrard Street and Alton Avenue, Torontoist has been able to track down fifteen additional ventilation stacks at various locations throughout the city.
Ask Torontoist illustration by Sasha Plotnikova/Torontoist.