OSIS Augmentation and Relief Sewer

DLZ designed the OSIS Augmentation and Relief Sewer, or OARS, for the City of Columbus. The backbone of the Columbus Wet Weather Management Plan, OARS will reduce combined sewer overflows downtown for a 10-year level of wet weather flow protection. With OARS operations, two billion gallons of combined sewage overflows receive treatment instead of overflowing directly to the Scioto River annually. This project benefits over one million people, bringing Columbus into compliance with the Clean Water Act.

In eliminating the 13 downtown combined sewer overflows, this project has spurred the development of the Scioto Mile and Scioto Greenways. The addition of these landmark parks has transformed the old riverfront into a vital public green space. Educational signs are planned in adjacent park areas to show project benefits. These signs will highlight how both the OARS tunnel and the odor control systems operate to protect the environment.

Milestone Capital Improvement Project

The new 20-foot diameter, 23,300-foot long OARS tunnel provides relief to the existing 82-year old Olentangy-Scioto Interceptor Sewer (OSIS). 180 feet below downtown Columbus, OARS extends from the Arena District to the Jackson Pike Waste Water Treatment Plant. At a cost of $370 Million, the OARS project is the largest capital improvement project in the history of Columbus.

DLZ put together the conceptual plans, design reports, and detailed construction specifications for the OSIS Augmentation and Relief Sewer. DLZ continuously interacted with city engineering staff throughout the project development, design, and construction process. DLZ’s role included managing the project design team, providing design services, and coordinating with subconsultants. The team also interacted with all project stakeholders and provided technical support services during construction. Specific design services included surveying, easement preparation, geotechnical evaluation, drilling test bore holes, and connection structure and weir gate design. Furthermore, the team performed hydraulic evaluations, drop shaft design, surge storage structure design, site civil design, structural design, ventilation and odor control design, and all public awareness activities.

In 2018, OSIS Augmentation and Relief Sewer was awarded an ACEC Ohio Outstanding Achievement Award and an ACEC Ohio Grand Award.

The DLZ team is eager to design solutions that meet your infrastructure needs. If you have any questions about the work we do, check out our Services page. We also highlight our diverse experience in our Project profiles. Additionally, feel free to contact us.




Local and State Governments


Columbus, Ohio