Grand Tour of Wilmette’s Sewers

During almost every discussion about Wilmette sewers, there comes a point when I realize: Wait a minute–we’re not talking about the same sewer system!

In fact, Wilmette does not have one sewer, or two, it has three, possibly four, distinct systems. Paris has nothing on us!

Can you find your neighborhood sewer systems on the map?

You’ll notice that west of Ridge Road there are two separate systems: a storm sewer (for runoff), and the sanitary sewer (for sewage from toilets, sinks, washers, etc.).

East of Ridge Road, there’s a combined sewer for everything (sewage and runoff). There’s also a relief sewer to handle overflows.

Take a Tour

It would be great if we could put on our hard hats and take an actual tour of our underground tunnels. But our sewers include miles of clay pipes that are only 8 to 12 inches in diameter. So instead our “tour” will have to rely on maps and fact sheets:

Just to make the whole thing more complicated, Wilmette is part of the Metropolitan Water Reclamation District (MWRD), which treats Wilmette’s sewage. In the “tours” (above), you’ll see a complex web of connections to the MWRD and its backup tunnels and reservoirs (TARP).

Test Your Knowledge

Now that you’ve picked up a few facts, see if you can answer these tricky questions:

Why won't Wilmette open the locks to stop sewage backups?
Only the MWRD (not the Village of Wilmette) can open the North Shore Channel locks at Wilmette Harbor. Opening the locks only helps prevent basement sewage backups east of Ridge Road, not for the rest of Wilmette.
Why is there flooding on eastside streets, despite sewer improvements?
East Wilmette is now served by the old combined sewer (flowing into MWRD) and a new relief sewer (flowing into an MWRD backup tunnel). This reduces flooding, sewage backups, and combined sewer overflows. But the new system also relies on temporary, limited “ponding” on streets to slow down stormwater intake and prevent surcharging.
Why is the sanitary sewer getting a new backup tank for storms?
The West Park underground storage tank is needed because the aging sanitary sewer system gets inundated by stormwater. Infiltration/inflow is caused by leaks in the pipes and manholes. Also, stormwater enters via homeowners’ service connections, and illegal or improper sump pump and downspout connections.
Why has the west side flooded so much in the last decade?
No big surprises here. The storm sewer was originally built for farmland and isolated housing developments. It hasn’t been substantially updated. So after decades of increased commercial and residential development, more intense rainfall, and relatively little capital investment, it’s not surprising that the system is failing.

Any Questions?

Creating this post was my biggest challenge so far… If you have any questions or corrections, please send input using the form (below). Thanks!


Find out about the Metropolitan Water Reclamation District (MWRD):

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