11 a.m. Storm Update

With more rain expected to fall throughout Cook County on Tuesday, the Metropolitan Water Reclamation District of Greater Chicago's (MWRD's) Tunnel and Reservoir Plan (TARP) continues to operate as designed with approximately 1 billion gallons of water being stored and more capacity available.

TARP, consisting of three reservoirs and four tunnel systems, is operating as designed to reduce flooding, improve water quality in Chicago area waterways and protect Lake Michigan from pollution caused by sewer overflows. To this point over multiple days of rainfall, there have been no reported 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.

The three reservoirs are currently holding approximately 1 billion gallons of water. Here is the breakdown:

• McCook Reservoir is 17.7 percent full holding 0.916 billion 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 1 percent full holding 0.085 billion gallons. The Thornton Composite Reservoir has 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.

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.