City of Columbus
OSIS Augmentation Relief Sewer
Construction Management Services
A crucial requirement of the consent order between the City of Columbus and the State of Ohio is to reduce the environmental impacts caused by Combined Sewer Overflows (CSOs). The OSIS (Olentangy Scioto Interceptor Sewer) Augmentation Relief Sewer, known as OARS, is the key component in meeting this goal. This sewer tunnel intercepts wet weather overflows that previously emptied into the Scioto River and carried the flows instead to the City’s wastewater treatment plants. H.R. Gray, an Anser Advisory Company, partnered with Black & Veatch for both phases of the project. Phase 1 involved excavating a 20-foot inside diameter hard rock tunnel with a total length of 4.4 miles. The gasketed precast concrete segmental lined tunnel will be approximately 170 feet below the surface. This phase included construction of three vertical shafts and a pump station. On a typical day, the OARS tunnel will be dry, but variable-frequency drive pumps located in the pump station shaft will engage during heavy storm events to convey combined sewer overflows from the OARS tunnel to the local wastewater treatment plants for biological treatment. Phase 2 included the construction of three vertical access shafts to direct flow from existing shallow sewers into the new deep tunnel. These drop structures dissipate energy and minimize air entry into the tunnel. A screening system was installed upstream of the Jackson Pike facility.