Dec. 20, 2010 -- Construction has begun on a hard-rock stormwater overflow and relief sewer tunnel 180 feet below the surface in Columbus, Ohio. The nearly 4.5-mile-long tunnel has a 20-foot diameter and will further limit combined sewer overflows (CSOs) into the Olentangy and Scioto rivers.
Black & Veatch, in association with H.R. Gray, is providing construction management for the tunnel project, which will augment the existing Olentangy Scioto Interception Sewer (OSIS).
The OSIS Augmentation and Relief Sewer project (OARS) is one of the largest capital investment elements to date in the Wet Weather Management Plan developed by Columbus in response to consent decrees requiring development of Capacity, Management, Operation and Maintenance and Long-Term Control Plans.
The OARS tunnel will be completed in two phases, with overall substantial completion and operational control expected in December 2014. Normally 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 Jackson Pike and/or Southerly wastewater treatment plants for biological treatment.