06/22/2026
11 a.m. Storm Update: MWRD’s TARP systems manages heavy rainfall
The Metropolitan Water Reclamation District of Greater Chicago (MWRD) has been working around the clock to capture billions of gallons of stormwater that have fallen across Cook County during recent storm events. According to the National Weather Service, the latest storm event had rainfall amounts that ranged from 0.7 inches at O’Hare International Airport, 1.7 inches at Midway International Airport, and nearly 2 inches in southern Cook County. Due to recent rain events, the MWRD TARP systems are holding nearly 9 Billion Gallons of stormwater, which is enough water to fill 13,600 Olympic-Size swimming pools.
The massive TARP infrastructure protects the region’s water environment and mitigates sewer overflows and basement backups for more than 3.71 million people served by combined sewer systems in the Chicago area. TARP consists of three reservoirs and four tunnel systems. As of 11 a.m., there had been no combined sewer overflows in Chicago area waterways. Here is the breakdown:
The McCook TARP system is approximately 92 percent full, holding 4.7 billion gallons. The McCook Reservoir has 3.5 billion gallons of capacity and serves central Chicago and 36 municipalities covering 252 square miles on the Des Plaines and Mainstream Tunnel Systems.
The Calumet TARP system is approximately 48 percent full, holding 4.1 billion gallons. The Thornton Composite Reservoir has 7.9 billion gallons of total capacity, including 4.8 billion gallons 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. The Majewski Reservoir has 350 million gallons of total capacity, serving 11 square miles on the Upper Des Plaines Tunnel System, covering Arlington Heights, Des Plaines and Mount Prospect.
Learn more at MWRD.org/News:
https://mwrd.org/news/11-am-storm-update-mwrds-tarp-systems-manages-heavy-rainfall
