Wilmette is part of the Metropolitan Water Reclamation District (MWRD) of Greater Chicago. And, I’ve realized, things get complicated when you share a sewer system with 9.5 million people!
Just to add to the complexity, the whole system ultimately flows into the Chicago River. And that river, which should drain northeast into Lake Michigan, has been re-engineered through a system of locks and pumping stations, reversing its direction, to carry treated waste water south, away from the lake.
With this as the backdrop, here’s my “shaggy dog” story for the last week of a rainy spring season in Wilmette…
Sunday: Fun On the Beach
During a break from the rain on Sunday, we headed to the Wilmette beach. The water was beautiful, flat, and clear–a little cold for us, but great for our dog Ellie:
Sunday, June 14, at the Gillson Park Dog Beach.
Monday: Rainy Day
On Monday, the day of the big Blackhawks game, it poured rain. June had started off pretty wet, so I double-checked the basement and sump pump. (All good!) Then I went online to find out: istheresewageinthechicagoriver.com
The answer from the Open City app was “Yes.” Data supplied by the MWRD indicated that sewage had already started overflowing into the Chicago River, even before Monday’s rain.
Overflows from Old Combined Sewers
Digging a little deeper, I found an MWRD report for the previous 24 hours:
Combined Sewer Overflow (CSO) Map (Source: MWRD June 14, 2015)
Red lines on the map mark areas affected by combined sewer overflows (CSOs), which are as bad as they sound.
Old style combined sewers, including the system that serves Wilmette’s east side, are designed to drain both runoff (from storms) and domestic sewage (from toilets, sinks, etc.), and transport it all to Water Reclamation Plants (WRPs) for treatment.
During heavy rainfall, combined sewers are inundated by storm runoff. Eventually, MWRD treatment plants can’t keep up, and the tunnel and reservoir storage becomes full. Then sewage can back up into basements of homes and businesses connected to the combined sewers (that is, east of Ridge Road, in Wilmette).
To relieve pressure and prevent sewage backups, the combined sewers in Greater Chicago are allowed to overflow into local rivers, at a number of outfalls that the MWRD monitors. Based on the map, it appeared that Wilmette’s own combined sewer system had overflowed into the North Shore Channel (top right).
Monday Night: Wilmette Locks Open
While running errands later in the day Monday, I listened to tornado alerts on the radio, watched the downpour, and decided to check out the Wilmette locks, located just west of the dog beach in the first photo:
Wilmette Locks and Pumping Station, June 15, 2015.
The locks and pumping station separate the North Shore Channel from the lake, and force the channel to flow south into the main Chicago River. But to my untrained eye, the water level looked high. As the level rises, there’s a risk of flooding along the banks. And if the channel rises above the combined sewer outfalls, sewage could back up into the basements of homes connected to the combined sewers.
Shortly before the Blackhawks game started, I checked the MWRD Facebook page and found the announcement: “Gates opened at Lake Michigan.” When the MWRD opened the Wilmette locks, rainwater and sewage flowed into Wilmette harbor and Lake Michigan.
Tuesday: Beach Closed Due to High Bacteria
The morning after the locks were opened, the beach was closed:
Gillson Beach closed due to high bacteria levels, June 16, 2015.
For the moment, our shaggy dog would have to stay on high ground.
So far this year, there have been 10 days of CSOs. Last year had a total of 41 CSO days.
Links:
Combined sewers are likely to overflow because they’re designed to clear away stormwater, but the aging systems also take in extra stormwater due to infiltration and inflow.
More About Wilmette’s Combined Sewer Overflows
MWRD Tunnel and Reservoir Plan (TARP) to Prevent Combined Sewer Overflows
Still confused by the modern use of these controlling works. During regular weather operations – which is most of the year – the channel is kept well below the level of the lake. To my mind, this would mean that you’d only need gravity to flush the channel during regular operations. On the other end of things, during rare storm events that fill the channel, you’d only need gravity to backflow it into the lake, right? So, it’d seem to me that this structure operates more as a controlling works – like the Chicago & O’Brien locks – than as a pumping station.
In fact, the only kind of scenario I can imagine where you’d need to pump water would the rare times when the lake falls below the level of the water in the channel AND the channel’s water is for some reason deemed to be too low (though still higher than the lake). Am I not understanding something, here?
Watched a short video on the changes to the structure done over a decade ago, but didn’t really understand what they changed or why. Apparently, two of the pumps were taken out of commission, but the tunnel left open? Why? The only part I understood was the reconstruction of the lock to make emergency backflow operations easier. But the changes to the pump tunnels went completely over my head so that I still have no idea how this structure is regularly used.
I’m not an expert on the Wilmette locks. Your first paragraph, I believe, describes the typical scenario. Right next to the locks is the shaft down to the Tunnel and Reservoir Plan (TARP) system, which the Metropolitan Water Reclamation District (MWRD) built to handle combined sewer overflows during storms. So if the eastside of Wilmette gets a severe storm and the old combined stormwater/sewage system overflows, then it can flow into the TARP shaft to await processing. If there is still too much overflow into the channel, the MWRD can open the locks, draining the channel into Lake Michigan, so residential areas along the channel are not flooded. As you point out, there are probably cases where the MWRD has to use pumps instead of gravity to handle water exchange at the locks, but I’m not really an expert on this. You could try to get more information at the MWRD facebook page: https://www.facebook.com/MetropolitanWaterReclamationDistrict
If you have the time, a virtual MWRD event this Tuesday afternoon could answer all your questions.
Here’s the event announcement:
Metropolitan Water Reclamation District of Greater Chicago
Learn about the work of the #MWRD on our next virtual tour.
When: Apr 11, 2023 02:00 PM Central Time (US and Canada)
Register in advance for this meeting:
https://us06web.zoom.us/meeting/register/tZYudeGqqDItH9c5NxMd5GxHze5rpZtQkUKa
After registering, you will receive a confirmation email containing information about joining the meeting.
If you can’t attend…
You can learn more about the Chicago Area Waterway System here:
https://mwrd.org/chicago-area-waterway-system
I figured this out, and it boils down to the change in purpose of the system. When originally constructed, the only purpose of the channel was to use lake water to dilute untreated sewage discharged into the channel. Anyway, this meant that flow from the lake had to be constant, and you couldn’t do that with gravity given the relatively flat elevation of the system. So it need pumps to provide a continuous flow; this meant the channel was always higher than the lake level. The purpose changed a bit with the development of modern water treatment plants and the completion of the North Side (now O’Brien) Water Reclamation Plant in 1928, though diversion was still needed for water quality purposes.
The big change came in 1939 when the Chicago River Controlling Works was completed closing the system to the lake completely. This allowed them to manipulate the water level in the canal system, and this also allowed them to switch the purpose of the channel was a dilution canal more towards flood control. Being able to keep the water level at a fairly consistent (lower) level was good for both navigation, flood control…and it meant they could use gravity at Wilmette for the diversion still needed for water quality improvements, which was much cheaper than using the pumps.
So, yeah, the pumps are almost never used, these days, but provide an option for diversion in the rare instance the in which Lake Michigan’s water level would fall below the legal minimum water level the channel must be kept at.
Thanks for that research. I’m curious where you found more information? Also, anyone on the CSO alert will have discovered that the Wilmette locks and the control gates in the loop in Chicago opened yesterday to release the sewage/rainwater that was overfilling the North Shore channel and Chicago River.
Oh, it was a lot of different sources online. But a big help was I was able to come across some of the “Draining Chicago” books by Richard Lanyon. They go into great detail about the system and its history.
BTW, I also learned that backflows are more common at Wilmette because it has a much smaller storage capacity than the main stem Chicago River and Calumet Rivers and because of its distance from Lockport. But because of the smaller capacity, the backflows are usually smaller, volume-wise, than at the other two controlling structures.
Yeah, Chicago got hit hard, yesterday. So did Detroit which had to close a few flooded freeways. Climate change is making things wetter in this region, at least during our wet seasons. And both of these cities are basically built on old lake beds with poor drainage, so even a little extra water overloads the system.
As for that last set of questions dealing with the reconstruction of the facility a decade ago, since pumping is barely needed today, removing two of the pumps allows for more/quicker diversion by gravity in either direction for diversons of emergency backflows. Prior to this, diversion in either direction could only be accomplished via the lock, and was thus limited by the size of the lock. The change to the lock also allows for more control of the diversion. Apparently, prior to this renovation, backflows into the lake via the lock could create small tidal waves in the harbor, which could damage boats or infrastructure there. This allows them to do more controlled backflows or diversion.
Disgusting,Is what they do to lake Michigan,
The sewer will always be in the lake.
It should be a crime.