By rosebell
The Lower Olentangy Tunnel is an impressive undertaking. Located at an average depth of 50 feet underground, the 12-foot-diameter tunnel has been under construction since early 2021.
By the time it is complete, in September 2026, it will be about 17,000 feet long and will help to keep our rivers and streams cleaner by providing a safe place to divert the overflow of untreated sewage from our city’s century-old network of underground pipes during heavy rains.
The $247 million project is being funded by the utility rates that residents pay the Columbus Department of Public Utilities, with financing provided by a below market-rate loan from the Ohio Environmental Protection Agency.
Unlike most of the construction projects that Columbus Underground covers – in which buildings get taller and more noticeable the longer the work goes on – this one has remained mostly invisible to the general public throughout the entire project.
There are a handful of places where work is happening on the surface – access points near Tuttle Park and at Goudy Field, near the intersection of Olentangy River Road and West Third Avenue – but even that work is mostly taking place behind construction fences.
Representatives of the Department of Public Utilities, Granite Construction and Black and Veatch Construction recently took Columbus Underground on a guided tour of the 2.5-acre Goudy Field site, the 80-foot-deep access shaft, and the tunnel itself.
We didn’t get to see the Tunnel Boring Machine (TBM), since it is currently parked for maintenance about 5,400 feet to the north, under Olentangy River Road, close to where Bravo Italian Kitchen sits.
The main access point and staging ground for the project is the Goudy Field site, which is where the new tunnel running north joins with a south tunnel that connects with the larger OSIS Augmentation Relief Sewer (OARS) at Vine Street in the Arena District. The OARS tunnel was built from 2011 to 2016 – it is deeper and mostly runs through rock, while the Lower Olentangy Tunnel is traveling through a looser conglomeration of gravel, dirt, and the occasional boulder.
The TBM not only digs and removes the dirt, it also builds the concrete walls of the tunnel itself, placing pre-cast segments in place as it goes.
“Imagine trying to dig a tunnel at the beach, it’s going to collapse,” said Project Engineer Maria Chastka. “So this machine, we put out a pressure bubble in front of us, either with air or [with] our conditioning system, which is a foam-air mixture, to create a pressure bubble so the ground doesn’t collapse…then we keep that bubble solid as we excavate, and then any over-excavation that’s outside of these [tunnel wall] sections, we grout around it, so we don’t get settlement.”
The grout is pumped in from above, which is why parts of Olentangy River Road around Lennox Town Center were recently closed off.
The Goudy Field shaft extends 80 feet below the surface. A large crane transports people, machinery and tools in and out of the shaft. When the TBM is in operation, it also delivers the concrete segments that make up the tunnel wall, and removes the dirt and debris that is being excavated (referred to as “muck” by the construction team).
The muck is processed on site; excess water is squeezed out and filtered before being returned to the city system, and the leftover dirt itself is placed in dump trucks to be delivered to Shelly Materials on the South Side. The company is using it to fill in a limestone quarry that has reached the end of its lifecycle.
Chastka said that Granite has 94 hourly employees working at the site. The work continues 24 hours a day, in three shifts; there are typically 11 people on the TBM itself while it is digging and constructing the walls of the tunnel.
In 2026, when the project is scheduled to be completed, the machine will have made its way to Tuttle Park, at which point the access shaft there and at the Goudy Field site will be covered up. At Tuttle Park, trees and landscaping will be planted and a permeable parking lot installed for park users and visitors to Tuttle Pool. The Goudy Field site will be landscaped as well but will reman mostly empty.
By that time, the city will likely have settled on a plan for the next tunnel.
Jeremy Cawley, Project Manager for the Department of Pubic Utilities, said that continued population growth, along with Intel and other big project announcements, have led the city to take another look at the need for an extension of the tunnel that is now under construction.
“We’re now basically modeling the system again,” he said, adding that the new tunnel would continue north from Tuttle Park, perhaps as far as North Broadway in Clintonville. “There’ll be another one, I don’t know if it’s going to be as big as this one, but we’re always looking ahead.”
