Where Does that Water Go When it Rains A Lot?

I did something super nerdy yesterday.

I had the opportunity to go on a tour of the Metropolitan Water Reclamation District of Chicago‘s McCook Reservoir and Mainstream Pumping Station.

 

MWRD

The circular entrance of MWRD is approximately the same size as the tunnels

 

Have I bored you already? Just wait.

The Mainstream Pumping Station is one of three stations designed to capture combined sewer overflows (where both sanitary and storm flow go through the same pipes) from an area of 375 square miles. Remember when I wrote about all the poop in the Chicago River? This would help alleviate that from happening.

When it rains a decent amount, all of the impervious surfaces of the city (roads, sidewalks, buildings) keep the rain from seeping back into the ground, causing it to run off into the city’s combined sewers.

The station is part of the Tunnel and Reservoir Plan which is designed to eliminate waterway pollution caused by combined sewer overflows and provide an outlet for flood waters. Phase I of TARP, intended primarily for pollution control, is made up of four distinct tunnel systems including Mainstream.

It consists of 31 miles of tunnels 240 to 300 feet below ground.  Sewage and stormwater entering the tunnels are carried to the Mainstream Pumping Station, where it is pumped to Stickney Water Reclamation Plant, the largest wastewater treatment plant

IN THE WORLD.

The McCook Reservoir is currently under construction and, when completed,  will have a total capacity of 10 billion gallons. It will be as long as 17 Soldier Fields stacked side by side (or it was 11, can’t recall exactly what the tour guide said!). When fully completed in 2029, the McCook Reservoir will provide more than $143 million per year in flood damage reduction benefits to 3,100,000 people in 37 communities.

MWRD2

McCook Reservoir will be ready to handle stormwater by the end of 2017.

 

So here is an easier explanation of how this works:

  1. It rains a lot
  2. The rain runs over sidewalks and roads and into the sewers
  3. When enough stormwater enters the sewers it can combine with the sewage sewer, resulting in a combined sewer overflow
  4. To prevent this, the stormwater drops into deep underground tunnels
  5. The water travels to a reservoir like McCook
  6.  The reservoir acts as a giant holding tank where stormwater is held until the water treatment plant has the capacity to handle it
  7. When it does, the Mainstream Pumping Station will pump the water to the Stickney Water Reclamation Plant
  8. The water is treated
  9. The treated water is released into the waterway
  10. Flooding and CSOs are prevented

That’s it!

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