Inspecting the Interceptors

A guide to Montreal’s interceptor sewer network and the traces of it to be found within the visible urban landscape

Riverside interceptor regulating chamber access structure.

Inspecting the Interceptors

A guide to Montreal’s interceptor sewer network and the traces of it to be found within the visible urban landscape

A typical interceptor manhole cover. C.U.M. is the abbreviation for Communauté urbaine de Montréal.

If there’s one thing that strikes fear into the hearts and minds of Montreal drainers (all three of us), it’s the island’s deep-level network of interceptor sewers. They are big concrete tunnels (up to 14.5 meters in diameter), often running at 100 feet below grade and with a ferocious amount of raw sewage coursing through them. All the wastewater of Montreal eventually drops down into one of these three tunnels. Our biggest fear is that we’d somehow end up going straight down there with it.

Because of this, we tend to keep our distance from anything marked “Intercepteur” and avoid passing through sections of sewers that come close to emptying into them.

Fortunately, there are  still ways to have a look at the network from a safe distance.

The interceptor’s primary role is to collect the island’s sewage and storm runoff and transfer it to the island’s  treatment plant before it has a chance to flow into the surrounding water.  This might seem like common sense, but Montreal didn’t even have a functioning treatment plant until 1987 and at that time only a portion of this network had been completed. It would take eight more years before the entire system was completed, twenty five years after its construction was first ordered.

The network is divided into three distinct parts and looks a little something like this:

The island of Montreal’s three interceptor lines (shown here in red) and locations of various control structures.

Downtown Montreal’s sewage falls into the Southeastern interceptor before being fed by gravity towards the treatment plant in Pointe-Aux-Trembles a good twenty kilometers away.

Detail showing typical interceptor and collector sewer intersection. A pumping station sits at the point where these lines meet.

Most of the time this system works quite well and everything gets treated before being discharged back into the environment. The problems come during prolonged periods of rain. The treatment plant reaches maximum capacity, leaving no choice but to let the excess flow drain out into the open water. These combined sewer overflow (CSO) events are symptomatic of older cities like Montreal, and not surprisingly are the source of much pollution.  However, it’s somewhat of a small price to pay given that before this system was put in place, raw sewage was flowing out into the environment 24/7 every day of the year. Once you know this,  it’s hard to complain about the odd overflow taking place.

The network of tunnels is of course hidden from view,  but its corresponding  infrastructure can be found above ground if you know where to look. Roughly 70 components consisting of pumping stations, diversion structures, gate chambers and inspection points dot the urban landscape. Their designs range from quirky to elegant to mundane.

A few found in and around the downtown area:

One of the more ornate pumping stations at McGill and Wellington that also doubles as an “interpretive look-out” for tourists. Not surprisingly, there’s mention of the sewers below.

A more austere-looking regulating structure on Riverside adjacent to Highway Bonaventure.

Brutalist-style inspection shaft entrance structure on Notre Dame East near Pie IX blvd.

Ventilated panels covering the top of an inspection shaft.

The interceptor tunnels also provide a convenient way to get rid of snow after its been plowed from the streets. Perhaps not as convenient as just dumping it into river, but ever since the city prohibited it tossing it straight into the sewer system is the next best thing.

Bellerive Snow Dump at Notre Dame and Parthenais.

Panels covering one Bellerive’s three chutes used for snow disposal.

Further reading: Interception Network and Construction Stages.pdf

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