Storm Update 12:01 p.m. Friday January 31, 2025

After nearly 24 hours of heavy rainfall on a near frozen ground across Cook County, the Metropolitan Water Reclamation District of Greater Chicago's (MWRD's) Tunnel and Reservoir Plan (TARP) on Friday continued to operate as designed, by capturing stormwater, sewage and additional snowmelt and keeping it out of local waterways and local communities serviced by combined sewer systems.

TARP, consisting of three reservoirs and four tunnel systems, is currently holding more than 806.8 million gallons of water. Here is the breakdown:

• McCook Reservoir is approximately 19 percent full holding 673.8 million gallons. 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.
• Thornton Composite Reservoir is approximately 2 percent full holding 133 million 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 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.

TARP works to reduce flooding, improve water quality in Chicago area waterways and protect Lake Michigan from pollution caused by sewer overflows. The MWRD captures untreated sewage and stormwater in its TARP system and then conveys it to its water reclamation plants for treatment to be released back into the environment as clean water.

Before severe storms, the MWRD lowers the elevation of the Chicago Area Waterway System by diverting more flow at its Lockport Powerhouse, about 40 miles south of downtown. The MWRD is also working around the clock to manage the excess water coming into its seven water reclamation plants throughout Cook County. As part of the continuing Overflow Action Alert, the MWRD encourages residents to conserve water during rain events to save more capacity in local sewers. Sign up to receive direct Overflow Action alerts via text: https://tinyurl.com/MWRDtext