Dig Indy tunnel system to soon keep 5 billion gallons of sewage out of Indy waterways

INDIANAPOLIS — Nearly a football field below the surface of the Citizens Energy Southport Wastewater Treatment Plant is a huge, man-made cavern.

By the end of the year, all of the sewage in Indianapolis will flow through it, instead of flowing into Indianapolis waterways.

”The cavern is about 100 feet front to back, about 60 feet side to side and 70 feet high,” said Mike Miller, the Manager of Engineering for Citizens Energy Group.

The cavern took more than seven months to make and 100 tons of explosives. Despite the demolition, Miller said the noise was barely noticeable at the surface.

”In the immediate vicinity, it feels like a low thunder rumble,” Miller said.

The cavern and the heavy, mechanical pumps inside of it will handle all of the Indianapolis sewage from the Dig Indy tunnel system.

”They can produce up to 30 million gallons each day through these pumps,” Miller said.

The network encompasses more than 28 miles of six interconnected, deep rock tunnels 18 feet in diameter. More than 8 billion pounds of rock have been drilled through for the project. For the past 15 years, the tunnels have been built right underneath Indianapolis at the cost of $2 billion.

The final tunnels in the Dig Indy system will be online by the end of 2025. Dig Indy is expected to handle approximately 5 billion gallons of sewage each year. That’s tough to picture, so Miller compares it to Lucas Oil Stadium in downtown Indy.

”If you took the roof off that stadium and filled that up 17 times, that’s 5 billion gallons,” he said.

As Dig Indy has come online with the completion of four of the six tunnels, 7 billion gallons of sewage have already been captured, kept out of waterways and treated.

In the past, when Indianapolis saw heavy rain, the current sewer system would’ve been overwhelmed, allowing sewage to flow into waterways to the tune of 5 billion gallons each year.

The goal of the Dig Indy system has been to make Indianapolis compliant with the EPA Clean Water Act. Miller said the positive environmental impacts are already beginning to show in the White River. 

”There are 1 or 2 organizations that are looking at different fish species that may start to reappear in the downtown area that have already been wiped out,” Miller said.

In a way, that sewage will still go into the White River, just after it’s been treated. 

”All of the flow from the tunnel system makes its way to this station, into this building and then ultimately gets pumped up almost 300 feet to the ground surface over into our Southport Treatment Plant,” Miller said.