Following heavy rains this weekend, the Metropolitan Water Reclamation District of Greater Chicago’s (MWRD’s) Tunnel and Reservoir Plan (TARP) continues to maintain capacity and operate as designed.

The TARP system, which is comprised of three reservoirs and adjoining tunnels, continues to capture stormwater and untreated wastewater to protect area waterways and Lake Michigan from pollution, while also mitigating flooding for a 375-square-mile area serviced by combined sewers in Chicago and 51 suburbs.

The three reservoirs are currently holding more than 2.345 billion gallons of water. Here is the breakdown:

• McCook Reservoir is 39.6 percent full = 1.389 billion gallons
The McCook Reservoir has 3.5 billion gallons of capacity, serving 252 square miles on the Des Plaines and Mainstream Tunnel Systems.

• Thornton Composite Reservoir is 12.2 percent full = 0.956 billion gallons
The Thornton Composite Reservoir has 7.8 billion gallons of capacity, serving 91 square miles on the Calumet Tunnel System.

• Majewski Reservoir is empty = 0 gallons
The Gloria Alitto Majewski Reservoir has .35 billion gallons of capacity, serving 11 square miles on the Upper Des Plaines Tunnel System.

The rains falling late Saturday into Sunday were heavier in southern Cook County. According to the National Weather Service (NWS), more than 5 inches of rain was measured in South Holland and Harvey but higher rainfall totals “likely fell in the Calumet City, Dolton, and Burnham areas.”

Few local sewers have capacity to handle these rain totals and convey this flow to the MWRD’s intercepting sewers and TARP infrastructure. The MWRD is working around the clock to manage the excess water coming into its seven water reclamation plants throughout Cook County, but the MWRD also encourages residents and business owners to contact their local municipalities to report flooding.
The public can conserve water during rain events to reduce flooding and protect the area’s water environment. Wait to run the dishwasher, shower and/or do the laundry. Sign up to receive direct Overflow Action alerts via text.