OARS Deep Sewer Tunnel

The OSIS (Olentangy Scioto Interceptor Sewer) Augmentation Relief Sewer, or OARS, is a critical component in meeting the requirements of an USEPA Consent Decree aimed at controlling combined sewer overflows into the Olentangy and Scioto Rivers. The deep sewer tunnel intercepts wet weather overflows that used to empty into the rivers and carries them instead to the city’s Jackson Pike and Southerly wastewater treatment plants.

The overall length of the OARS tunnel is approximately four and a half miles, and includes three relief structures that divert wet weather combined sewer flow from the OSIS to the OARS tunnel. The tunnel’s location, roughly 180 feet below ground, includes special drop structures (or vertical shafts) to direct flow from existing shallow sewers to the new deep tunnel. A screening system upstream of the Jackson Pike facility and a pump station empties the tunnel directly to the treatment plants after significant rain events, utilizing as much treatment capacity as possible.

The project was constructed into two phases. Phase 1 involved digging a 20-foot diameter segmentally-lined tunnel with a total length of about 23,300 feet and three large diameter drop shafts (Shafts 1, 2 and 6) to provide relief to the existing OSIS trunk sewer and direct combined storm water flows to the Jackson Pike or Southerly treatment plants. Phase 2 involved the construction of three additional drop shafts (Shafts 3, 4 and 5), various manholes and flow diversion structures, and installation and commissioning of an integrated submersible pump system in Shaft 1.