chicago river, north branch, combined sewer overflow, river as public space

Combined Sewer Overflow: How a Using Rain Barrel can help Keep Sewage Out of the Chicago River


Did you know that when it rains in Chicago we dump raw sewage into the river?

Check out the official outfall sign which asks for calls “if discharge is observed during dry weather.”  If its been raining – there’s no need to call the hotline – the Metropolitan Water Reclamation District of Greater Chicago already knows it’s happening.  

No one is happy about it … but it’s no accident.

cso warning
So how can this be our official plan?  Well Chicago hasn’t been known for treating our waterways with care.  The South Fork of the Chicago River is still known as Bubbly Creek – so named because it used to bubble with the gasses released by the decomposing blood and carcasses tossed in the river by the meat packing plants.  We’ve stopped doing THAT but our Combined Sewer Overflows (CSO) are still a problem that has its roots deep in city history.  The good news is that steps are being taken to address the problem.

How Sewers Work

American Cities use two systems for collecting and removing storm water from our overly hard-scaped urban areas.

The first is known as the Combined Sewer System (what we have here in Chicago) in which all the waste water in the city is collected in a single system of drains.  So every drop of water that runs down your bathroom sink drain, is flushed from your toilet or falls on the street out front goes into the same sewer line and is carried away to be treated.  The system looks something like this (image adapted from the EPA.

combined sewer

Sewer systems built later (after WWII) tend to feature separate tunnels for sewage and storm water which means that only the sewage water needs to be treated and there is no system of sewage overflow into waterways required by extreme rain.  Note: Even separate storm water sewer systems are flushing our lakes and river ways with all sorts of highly concentrated pollutants.   Those systems work more like this:

separated sewer

Water Treatment – Then and Now

When people first began to realize all the consequences of drinking contaminated water – epidemiologist, Dr. John Snow, first linked a Cholera epidemic to sewage-contaminated wells in London in 1855 – we turned our attention to water treatment.

Early treatment systems used a combination of sand filtering (to strip out particulate matter) and chemicals like chlorine to kill bacteria and other disease causing microbes before water was cycled into municipal systems.  Today the process is remarkably similar to that early model with a series of settlement tanks, filtration systems and chemical treatments to

In theory sewer water is treated in this manner before it exists the system.  We already know that theory and practice are not the same thing!

So What Happens When There is Too Much Water?

Water treatment systems processing the water from combined sewers can be overwhelmed by extreme flood events.  When that happens – there is overflow at the outfalls.

A handy (if alarming website) announces what days raw sewage overflows are occurring on the Chicago river system, as has happened 454 times since 2007 (that’s an average of about 60 times a year).  If there is a CSO, the website also points out the number of locations and where they are on the river.  You can click a link to see the facts for each of those 454 previous events on the website too.

When the overflow is extreme (as it was just before the Fourth of July weekend) river locks are opened and sewage is released into Lake Michigan as well.  Hence the beach closures common on days after heavy rainfall!

Unsurprisingly, the first response to this problem was to throw more infrastructure at it.

In the 1970’s Chicago’s Metropolitan Water Reclamation District began a huge public works project the Tunnel and Reservoir Plan (TARP) which is designed to hold extra storm water in huge underground catchment areas until it can be processed by wastewater treatment plants after the flooding has passed.  Similar projects have been undertaken in other cities with the result of reducing (but not eliminating) overflow events.

Well and good.  If we are going to mix microbe carrying human waste water into our storm drains, we need to treat all of that water before it goes either into the water ways again or into our drinking water system.  We certainly can’t NOT treat that water.  We need to handle as much of it as possible and it isn’t feasible at this point to convert combined sewer systems  into separated sewage systems by digging under existing cities to install a secondary system of drains.  Still these big infrastructure programs are expensive and problematic.  What if there were a simpler solution?

Green Solutions to Urban Storm water Problems

CITIES CAN REDUCE THE PROBLEM DRAMATICALLY by preventing water from entering the storm sewer system in the first place.  There are a number of green infrastructure alternatives to explore.  The NRDC (National Resources Defense Council) boils it down thus:

“With green infrastructure, stormwater management is accomplished by letting the environment manage water naturally: capturing and retaining rainfall, infiltrating runoff, and trapping and absorbing pollutants.”

Elegantly simple in concept – it just means keeping water where it falls instead of whisking it away from that spot into a drain.  There are many ways to accomplish this.  Urban trees catch and hold rainwater both with their leaves and roots.  Sidewalk plantings and even bioswales can catch and retain stormwater that falls on them and from nearby hardscape.  Green roofs on commercial buildings can dramatically reduce the amount of water running in gutters and drains.

Chicago has been piloting a number of these policies and is featured in this NDRC document on Green Strategies for controlling Stormwater and Combined Sewer Overflows.  Scroll to page 23 to check out the initiatives listed.  Green roof programs (including the one on city hall), permeable paving in alleys and bioswales have all been tested by the MWRCD in their attempt to minimize stormwater.

What YOU can do about it

There are obvious ways to avoid cycling perfectly clean potable water back into the sewage treatment system –

A more extreme way  is to entirely unhook yourself from the water treatment system by not contributing your waste to it.  Alternatives to conventional plumbing like composting toilets, which we wrote about in May (Dishing the Dirt on Composting Toilets) and using a grey water system to handle the rest of your household water use.

But just as important as minimizing your personal, household water use is helping keep rainwater out of the sewer system.  As we showed above – when too much water gets into the city sewer system that rainwater AND your untreated household sewage end up overflowing into our local water ways.  But that can be prevented or at least minimized by reducing the amount of storm water that gets into the sewer system.

  • planting and maintaining yard and street trees
  • maximizing the permeable green space in your yard if you have one
  • replacing driveways with permeable paving surfaces
  • catching water that falls on roofs in rain barrels for yard watering in dry seasons …

It may seem small but every drop of water you can keep out of the sewer system is water that won’t need to be processed and treated – and has no danger of overflowing into our local river systems.