Despite heavy rains overnight and into the morning, the Metropolitan Water Reclamation District of Greater Chicago’s (MWRD’s) Tunnel and Reservoir Plan (TARP), continues to operate as designed and proving essential in its ability to mitigate area flooding and protect the quality of area waterways from pollution. 

The three reservoirs are currently holding more than 2 billion gallons (BG) of water. Here is the breakdown:

McCook Reservoir is 54.6 % full = 1.95 BG

Stage 1 of the McCook Reservoir has 3.5 billion gallons of capacity, serving central Chicago and 36 municipalities covering 252 square miles on the Des Plaines and Mainstream Tunnel Systems. Stage 2 of the McCook Reservoir is currently being excavated and will add 6.5 BG of capacity.

Thornton Composite Reservoir is 1% full = 85 million gallons 

The Thornton Composite Reservoir has 7.9 BG of capacity, including 4.8 BG of combined sewer capacity, serving 91 square miles on the Calumet Tunnel System, covering the South Side of Chicago and 13 south suburban municipalities.

Majewski Reservoir is empty with 12 million gallons in the tunnels.

The Gloria Alitto Majewski Reservoir has 350 million gallons of capacity, serving Arlington Heights, Des Plaines and Mount Prospect across 11 square miles on the Upper Des Plaines Tunnel System.

Before severe storms, the MWRD lowers the levels of the Chicago Area Waterway System at its Lockport Powerhouse. The MWRD staff work around the clock to manage the excess water coming into seven water reclamation plants throughout Cook County. Although an Overflow Action Alert has not been issued to this point, the MWRD encourages the public to conserve water during rain events; wait to run the dishwasher, shower and/or do the laundry. 

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