Full Breakdown
Chicago’s Deep Tunnel System Nears Historic Capacity Amid Record Rainfall
7/7/2026, 3:57:30 PM
Historic Fullness of Deep Tunnel Reservoirs Triggers Flood Alerts
July 3-4 brought eight inches of rain, pushing the Thornton reservoir to 94 % of its 7.3-billion-gallon capacity and the McCook reservoir to 96-100 % full. Together they hold about 11 billion gallons, prompting flood alerts for eleven municipalities.
Historical Development and Purpose
The Deep Tunnel, launched in the 1970s, comprises over 100 miles of underground tunnels that channel stormwater and sewage from Chicago and surrounding suburbs into three reservoirs—Thornton, McCook and Majewski—to protect regional rivers and Lake Michigan.
Key Data from the Event
The National Weather Service recorded over eight inches of rain in 48 hours, adding to a month-long total exceeding eight inches. The city’s 311 system logged about 400 basement-water and 600 street-flood reports. Affected municipalities include Blue Island, Calumet City, Dixmoor, Dolton, Glenwood, Harvey, Lansing, Phoenix, Riverdale, South Holland and Thornton.
Residents’ On-the-Ground Experiences
Resident Jeff Melone said he had never seen the reservoir at this level. Tinley Park resident Cassie Haan reported a 50-year-old tree toppled and considered a generator for her sump pump. Park Forest resident Aleiya Jennings described repeated basement flooding, water bubbling from storm drains, and drywall repairs.
Official Statements & Agency Responses
Climatologist Trent Ford warned that saturated soils and near-full reservoirs raise flood risk even from moderate rain. Margaret Frisbie of Friends of the Chicago River urged a regional “blanket” of natural areas for storage. The Metropolitan Water Reclamation District said water will be pumped to treatment plants and then released to the Little Calumet River.
Criticism, Opposition, and Calls for Action
Experts say the Deep Tunnel alone cannot prevent future floods and recommend expanding greenspace and storage technologies. Park Forest board member Randall White noted the community lacks “millions of dollars” for drainage upgrades, while residents cite aging 75-year-old storm drains as a failure point.
Conflicting Reports & Information Gaps
WBEZ reports the McCook reservoir fluctuated between 96 % and 100 % full, but the Chicago Tribune article mentions only Thornton’s record level and omits current McCook data. The Majewski reservoir’s capacity is noted as less than three percent of total system volume.
Verbatim Quotes
- “We have inundated soils and nearly full reservoirs, meaning that the region-wide flood risk is higher, even from rain that is not particularly heavy,” — Trent Ford, Illinois State Climatologist
- “We need to blanket the region with natural areas,” — Margaret Frisbie, Friends of the Chicago River
- “I’ve never seen anything like this before. I didn’t think this was possible,” — Jeff Melone, resident near Thornton reservoir
- “All the storms got us thinking about getting a generator,” — Cassie Haan, Tinley Park resident
What's Next
The National Weather Service forecasts additional rain Thursday, keeping reservoirs near capacity. The McCook reservoir expansion, slated for completion by the end of 2032, aims to add billions of gallons of storage. Local officials continue to seek state and federal funding for drainage upgrades.
