Olentangy Scioto Interceptor Sewer (OSIS) Augmentation and Relief Sewer (OARS)
The City of Columbus, moving to address wet-weather combined sewer overflow issues, is building the Olentangy Scioto Interceptor Sewer (OSIS) Augmentation and Relief Sewer, more commonly known as the OARS. The concept of the OARS was presented by the City in the July 2005 Wet Weather Management Plan (WWMP) as a large volume conduit to serve two purposes: intercept and convey combined sewer overflows (CSOs) from the CSO regulators on the interceptor in the downtown area, and relieve the interceptor during wet weather conditions. The OARS project consists of the construction of 22,750 feet of 20-foot diameter, deep tunnel wastewater conduit that provides relief to the existing OSIS from just north of the Arena District in Downtown Columbus to the Jackson Pike WWTP. EMH&T performed the hydraulic analysis of the OARS. The model was used to provide flow estimates for various levels-of-service and to optimize the size and elevation of the OARS tunnel. Different operational conditions were evaluated to maximize treated flow and to develop a strategy to optimize flow between WWTP’s. In addition to the tunnel analysis, EMH&T designed “green” infrastructure to eliminate an existing combined sewer, which reduced wet-weather flows provides protection against potential surcharge conditions in Berliner Park due to the shallow nature of the OSIS.