CALUMET CITY | A heavy rainfall in the south suburbs Sunday night caused damage to a structure at Veterans Parks connected to the Deep Tunnel system that controls flooding across Cook County.
Metropolitan Water Reclamation District officials spent Monday at the park on Burnham Avenue investigating the damage, while also preparing for another round of rain Monday night.
Water district spokeswoman Allison Fore said that a junction shaft interceptor that is part of the Deep Tunnel system erupted because of pressure created by stormwater that overwhelmed the sewer system.
Water district officials said that some 1.8 inches of rain fell within an hour Sunday night. “An extreme rain … inundated the sewer system,” Fore said.
Water displaced air quicker than the air could be removed, which caused an eruption of dirt and rock. That created a sinkhole around the structure.
No one was injured, and water district officials said Monday they secured the area surrounding the structure.
The eruption created a shaft 30 feet across and 15 feet deep. Fore said debris from the eruption settled in parts of the park and in parking lots next door. One structure next door sustained flood damage in its basement, she said.
Repairs began Monday, with water district officials securing the perimeter of the site and cleaning up the debris.
Officials are trying to determine a plan to rebuild the structure in a way that reduces the likelihood that Sunday night’s incident could recur. Fore said it could take several months before work is complete.
Water district officials also said that implementation of the Thornton Reservoir beginning next year will act as a very large surge suppression tank for the entire Deep Tunnel system, also reducing the chance of such an event recurring.
According to the water district, the Calumet Tunnel system was full as of 10 p.m. Sunday. It can hold up to 620 million gallons of water, and is part of the Deep Tunnel system that can hold 2.3 billion gallons.
The mainstream tunnel, as of Monday, is 77 percent full, while the Des Plaines Tunnel is 51 percent full. But the Kirie Tunnel in the northwest suburbs is empty.