Projects Water

Olentangy Scioto Interceptor Sewer Augmentation and Relief Sewer (OARS)

Columbus, Ohio

The OARS tunnel is the backbone of the Columbus Wet Weather Management Plan, designed to reduce combined sewer overflows in downtown Columbus for a 10-year level of wet weather flow protection. With the OARS tunnel operational, nearly two billion gallons of combined sewage overflows receive treatment instead of overflowing directly to the Scioto River each year. This project benefits a community of over one million people, bringing Columbus into compliance with the Clean Water Act. Essentially eliminating the 13 downtown combined sewer overflows has allowed for the development of the Scioto Mile and Scioto Greenways, landmark parks in downtown Columbus, which helped transform the old riverfront into a vital public green space. Educational signs are planned in adjacent park areas to show how both the OARS tunnel and the odor control systems operate to protect the environment.

The new 20-foot diameter, 23,300-foot long OARS tunnel provides relief to the existing 82-year old Olentangy-Scioto Interceptor Sewer (OSIS). The OARS tunnel is approximately 180 feet below downtown Columbus, and 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 improvements project in the history of Columbus.

DLZ was responsible for putting together the conceptual plans, design reports, and detailed construction plans and specifications for the OARS project. 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, coordinating with various subconsultants, interacting with all the project stakeholders, and providing technical support services during the construction phase. Specific design services included surveying, easement preparation, geotechnical evaluation, drilling test bore holes, connection structure and weir gate design, 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, OARS was awarded a ACEC Ohio Outstanding Achievement Award and a ACEC Ohio Grand Award.