Montreal's Most Famous Sewer

With a scientific review of the plan, here’s an in-depth look at the southeast interceptor, Montreal’s most famous sewer

It’s 30 kilometres long, slightly narrower than a métro tunnel, and full of water and other things that go down your toilet and sink and the sewers on your street.

The city’s plan to shut it down for a week for repairs, maintenance and upgrades has caused a storm because it would involve dumping 8 billion litres of raw sewage into the St. Lawrence River.

With a scientific review of the plan due Monday, here’s an in-depth look at the southeast interceptor, Montreal’s most famous sewer.

Three projects

If the shutdown goes ahead, 12,000 litres of wastewater per second will flow into the St. Lawrence, via 24 submerged outfall pipes. Twenty-two of them will discharge waste 30 to 50 metres from the shore, with the remaining two dumping within a few metres of land. The city refused to tell the Montreal Gazette which pipes are close to the shore.

Teams of workers will be on the job around the clock, inspecting and cleaning various sections of the interceptor and tackling three projects, all of which requires the interceptor to be dry.

The priority project involves replacing a snow chute, with the rest of the work being done during the same week to take advantage of the fact that the interceptor will be empty.

Here’s what the city says about the work (total cost: $2.2 million):

Snow chutes:  Trucks filled with snow from downtown streets used to make their way to the Wellington snow dump, under an elevated section of the Bonaventure Expressway (at Wellington and Duke Sts.). There, every year, they dumped about 200,000 square metres of snow right into the southeast interceptor. With the city tearing down the Bonaventure and rebuilding the road at ground level, this snow chute has to be closed. In its place, the city plans to build a new one at Mill and Riverside Sts. less than a kilometre away. The location already has some of the required infrastructure. The new chute – 3.6 metres by 4 metres – is expected to be used by up to 26 trucks per hour, with snow falling 35 metres into the southeast interceptor.

Western part of southeast interceptor:  In 1997, a series of wood and steel structures were installed in this section to facilitate the installation of future snow chutes. The city later decided against building those chutes. Now, pieces of wood are falling off and being carried by water to the waste water treatment plant, where they block equipment. An inspection conducted in 2010 with the help of a robot found that the steel parts of the structure are also deteriorating. The city says the debris could damage pumps and reduce the capacity of the interceptor. Delaying the work increases the risk of major breakdowns of pumps and other equipment, which could lead to prolonged sewage overflows. The removal work is complicated. Workers will have to install scaffolding, dismantle the wood and steel structures and transport the pieces out of the interceptor using specialized equipment on wheels or tracks.

Source: Montreal Gazette

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