Columbus, Ohio’s Lower Olentangy Tunnel Reaches Boring Destination: Stormwater and Sewage Overflow Management is the Goal

      Columbus, Ohio’s Lower Olentangy Tunnel, a three-mile, 12-ft inner diameter tunnel in a 15-ft diameter hole, recently reached its destination, meaning the tunnel boring machine just broke through to complete the hole. It broke through a concrete wall at the bottom of a 50-foot hole near Tuttle Park. The tunnel is designed to divert stormwater from heavy rain/heavy runoff events away from the city’s sewage treatment plants and keep it from overwhelming them. Excess stormwater can be retained in the tunnel system until the wastewater treatment systems can handle it. The tunnel system will prevent sewage overflows from entering the Olentangy River, resulting in a cleaner river.

     The tunnel was bored by a 400-ft-long Herrenknecht tunnel boring machine, manufactured in Germany, which moves forward in five-foot increments. Construction began in 2021, the actual tunnel boring began in March 2023, and the tunnel system is expected to be completed in September 2026. It is a $250 million project. The tunnel averages about 50ft in depth. It is the second-largest project ever bid out by the city.

 According to WOSU:

“It connects with seven Combined Sewer Overflow (CSO) structures located along the lower portion of the Olentangy River by relieving the Olentangy Scioto Intercepting Sewer. These CSO structures are located at First Avenue, Third Avenue, King Avenue, Indianola Avenue, Frambes Street, Doe Alley and Hudson Street.”

“Project manager Jeremy Cawley told WOSU that before a project like this came online, the heavy rain would cause sewer overflow to go into the Olentangy River, presenting problems with water pollution and water quality for the key source of the city of Columbus' drinking water.”

"It'll be an overflow tunnel for the main trunks. And then we can hold it in the tunnel for a couple of days until the plant can handle it. Because that's usually what happens. The plants get overwhelmed and they just can't treat it all," Cawley said.

     Due to the large size of the project, the city constructed a railway track along the tunnel to help transport waste materials and rubble. Eventually, the tunnel system may be expanded north to the Clintonville area. The tunnel system is expected to have at least a 100-year lifespan.

   

 

 

References:

 

Lower Olentangy Tunnel keeping untreated water from our waterways. Sarah Converse. WSYX. June 4, 2025. Lower Olentangy Tunnel keeping untreated water from our waterways

Massive $250 million, three-mile Columbus sewer tunnel project reaches destination with a bang. George Shillcock. WOSU 89.7 NPR News. June 4, 2025. Massive $250 million, three-mile Columbus sewer tunnel project reaches destination with a bang | WOSU Public Media

Modern tunnel systems pave the way for the future. Herrenknecht. Tunnelling