Hidden Underworld: Diving deep into Toronto’s underground sewer system

The stench really wasn’t that bad.

As I descended down the grated metal staircase, I held my nose, expecting the smell to be eye-wateringly bad. However, what did hit me was a sudden sense of vertigo as my eyes adjusted to the semi-darkness of the vast chamber; I was suddenly 150 feet above a soup of city sewage and storm overflow deep beneath Lakeshore Boulevard in Toronto.

Flooding isn’t something that we think about unless the streets are running with water, but it’s something that Bill Shea, Director of Water, Collection and Distribution for the City of Toronto, ponders every single day. This is because all cities need a huge input of clean water and an equally large output of dirty water that needs to be collected and treated before it is released. Bill is the one that the City turns to ensure that the system runs smoothly.

On top of this already gargantuan task, a city like Toronto has many older sewers that were designed and built before we understood that dumping raw sewage into even a water body the size of Lake Ontario wasn’t a great idea and the population of Toronto was far smaller. The result is that these older systems can’t handle the input of both normal sewage flow when it’s combined with stormwater. So, in Toronto, the “combined sewer outflow” system meant that when a storm hit the city, the resulting water moving through the stormwater system often overflowed into the sewage system which then flowed directly into Lake Ontario, untreated.

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That’s now changing thanks to massive projects ongoing underneath the streets of Toronto. The vast chamber I was standing over not only ensured that I got my first experience with underground vertigo, but also ensured that far less untreated water is escaping into Lake Ontario.

Bill was getting a kick out of how hard I was gripping the steel railing that felt like the only thing keeping me from plunging into the horrible miasma far below.

“This tank [see image below] is one of three here in the western Beaches which is connected by 3.7 kilometres of tunnel, and each tank can fill up in about 20 minutes in a big storm,” explained. “Total storage is around 85,000 cubic metres.”

Mark Robison dives deep into Toronto's massive sewer systems
Mark Robison dives deep into Toronto's massive sewer systems

(Mark Robinson stands at the edge of a tank)

This shocked me given the sheer mind-boggling scale of the chamber, so I asked him how the system worked for spring flooding given that some storms can keep hitting the same area for an hour or more.

“The stormwater goes through what we call high-rate treatment. I don’t know if you’ve seen the building down on Cherry Street with all the weird angles, but that’s the newest addition to the system and is strictly dedicated to treating stormwater.”

He continued, “We let all the material in the water settle out in these large tanks, then run that clarified water through a very large UV system before it’s pumped out to the lake. At the same time, there are ponds, ditches and large tanks that collect and allow settling, and treatment to happen more slowly.”

He gestured down at the large collection of things sitting on the top of the water far below us.

"There are two ways we deal with the floatables—the junk that gets caught up in the snow of the winter when plowing and shovelling happen. Either they get pumped—and the pumps we use are very powerful because a lot of it is paper products like cups—it gets sent to the treatment plant, and then gets screened out and eventually on to a landfill. The other way they get dealt with is a bit more direct. After a few years, sediment builds up at the bottom of the tanks, and we literally drop a Bobcat front end loader down to clean it all up. And yes, we do hose it down afterwards. We like our Bobcats clean."

Mark Robinson: Giant underwater tanks catch excess rainwater in Toronto to prevent flooding
Mark Robinson: Giant underwater tanks catch excess rainwater in Toronto to prevent flooding

Toronto Water is responsible for all aspects of: drinking water treatment and supply; wastewater collection; and treatment stormwater management. (Mark Robinson/The Weather Network)

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I asked Bill about his most hated season and that made him laugh. I figured it was spring because of the melting snow, but I was wrong.

"Actually, we tend to get the intense storms that give us problems in the late summer and fall; you know, the huge thunderstorms that hit in late July or August. The problem is that these storms can hit very specific areas, and even if the sewer is designed for, say, 50 mm of rain, if the storm hits a very paved area that’s low lying with a fast runoff, we can get flooding. No sewer system can keep up with the intensity of some of those storms."

Bill isn’t ignoring the problem: "We are working to a master plan, increasing sewer size, adding in more tanks like this one, but most importantly, we are ensuring that the water being passed to the Lake [Ontario] is being treated before it gets there. The Don Central Waterfront is the largest project ongoing right now. The system comes down the Don Valley and the Coxwell area and will eventually incorporate these tanks as part of the whole system. This will let us hold the water until it can be properly treated."

What I really wanted to know was how this spring was shaping up for the existing system. He gave me a big thumbs up and said, "The lack of snow and, so far, no major storms incoming mean that we're in a really good place to handle things this spring."

The sunlight made me blink as I emerged back into the light of the day and stood on the innocuous grass hill that overlooked the Waterfront Trail near the CNE. My journey into the literal bowels of the city was far different from my usual adventures underneath storms, but now, when I see a storm rolling over Toronto, I won’t be able to forget that the aftermath of a storm involves a lot more plumbing than I figured.

For a behind the scenes look at Toronto’s massive underground sewer system, watch the video that leads this article (refresh the page to restart the video).