The Metropolitan Water Reclamation District of Greater Chicago (MWRD) expects to have two projects totaling $5 million to address odor mitigation near its Thornton Reservoir completed by the end of 2026, bringing total mitigation efforts over the past decade to $8.6 million, according to officials.

The massive Thornton reservoir, a south suburban quarry holding billions of gallons of stormwater and sewage that nearly filled up this past week, will take at least a month before it drains. Thornton is part of the Deep Tunnel flood-control system and resembles a canyon in South Holland. It takes in sewer wastewater during heavy storms that is later pumped out to the Calumet treatment plant at East 130th Street in the Far Southeast Side Riverdale neighborhood. For the first time since opening in 2015, the quarry filled to near capacity along with another flood-control reservoir known as McCook in Bedford Park.

The nearly 8 billion-gallon Thornton reservoir, which helps prevent flooding, was nearly full this week. The sewer water is slowly being pumped out but it will be weeks before the south suburban quarry is dry again.

The Deep Tunnel system did its job this week, keeping billions of gallons of storm and wastewater from flooding people’s homes following a deluge of rain over the 4th of July holiday weekend. But a whole lot of that water continues to stew in the massive Thornton reservoir, which serves the South Side of Chicago and 13 south suburban municipalities.

The Thornton reservoir has been in operation for 11 years, but residents say a persistent smell of raw sewage continues to spread through the village when heavy rain combines with heat, sometimes lingering for days. As of Thursday afternoon, the reservoir was 89% full, down from a record 94% level reached several days ago, following last weekend's storms. While the lower level eased flooding concerns, residents said the heavy rains brought another familiar problem. On Friday, the MWRD said says it expects to have two projects done by the end of the year to address the odor, totaling about $5 million.

The Metropolitan Water Reclamation District of Greater Chicago (MWRD) expects to have two projects totaling $5 million to address odor mitigation near its Thornton Reservoir completed by the end of December 2026, bringing total mitigation efforts over the past decade to $8.6 million, according to officials.