Columbus celebrated a significant milestone as construction crews completed the Lower Olentangy Tunnel, a three-mile-long sewer overflow tunnel designed to protect local waterways.On Wednesday, an excavation machine successfully penetrated the final stretch, marking the culmination of nearly four years of work.

The breakthrough occurred near Tuttle Park, where the excavation machine bored through a concrete wall at the bottom of a 50-foot hole. The event was met wiht cheers from contractor crews and columbus Water and Power employees.

Set to be fully operational by late 2026,the $250 million Lower Olentangy Tunnel aims to mitigate sewage overflow into waterways like the Olentangy River during severe storms,which are becoming increasingly frequent due to climate change.

The tunnel stretches three miles underground, from Tuttle Park to Vine Street near the Scioto River confluence. It connects with sewer lines, facilitating the flow between sewage lines and water treatment plants. The tunnel itself is 12 feet in diameter and runs approximately 50 feet below the surface.

This tunnel is part of a larger system designed to maintain clean waterways during heavy rainstorms, which are increasingly common due to climate change. It connects to seven Combined Sewer Overflow (CSO) structures along the lower Olentangy river, relieving the Olentangy Scioto intercepting Sewer. These CSO structures are located at Frist Avenue, Third Avenue, King Avenue, Indianola avenue, Frambes Street, Doe Alley, and Hudson Street.

Before this project, heavy rain woudl cause sewer overflow into the Olentangy River, leading to water pollution and quality issues for Columbus’ drinking water source. Project manager Jeremy Cawley explained the tunnel’s function:

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.

Jeremy Cawley, Project Manager

Cawley expressed his satisfaction with the project, noting its importance:

This is the biggest project I’ve been on. It’s actually,I think,the second largest the city’s ever bid. So yeah, it’s an honor to be on a project of this size.

Jeremy Cawley,Project Manager

He also mentioned the project’s nickname,Mighty quinn.

The moment the machine broke through the concrete wall was dramatic, with rock flying into the tunnel’s base and a white liquid spewing into the basin.

The $250 million project was primarily funded by city utility rates,with additional support from Ohio EPA loans. The city of Columbus is under two Ohio Environmental Protection Agency consent orders to enhance water quality and minimize human contact with waterborne pollutants by reducing sewer overflows into creeks and rivers during wet weather.

The scale of the project necessitated the construction of a railway track within the tunnel to facilitate the transport of waste, materials, and rubble.

Looking ahead, Cawley suggested the possibility of extending the tunnel further north towards the Clintonville area. He emphasized that the growth of Columbus, particularly the development of the New Albany Intel plant, is driving the need for similar infrastructure projects. He estimates the tunnel will have a lifespan of at least 100 years.

Upon completion,the Tuttle Park site will be capped with concrete,and the work area will be resurfaced,creating a parking lot near the Tuttle Park pool. Additionally, over 100 new trees will be planted in the area.