DLZ evaluated numerous alignments for the Lower Olentangy Tunnel (LOT) project. The primary factors evaluated included hydraulic analysis, a geotechnical evaluation, construction impacts, property acquisition requirements, an alternative cost evaluation, alternative schedules, and a comparative risk evaluation.
The recommended alignment for the LOT project consists of constructing 17,000 feet of 12-foot diameter tunnel. It will provide relief to the existing OSIS, Franklin-Main Interceptor, Kinnear Subtrunk, and Olentangy-Main Interceptor sewers from just north of the Ohio State University campus to the Arena District in downtown Columbus.
The size of the LOT will provide adequate conveyance capacity and inline storage to eliminate sewage overflows from the regulators located along with these sewers. Relief structures constructed on the existing sewers will enable the diversion of wet weather flows to the Lower Olentangy Tunnel. Adjustable weirs utilized on the relief structures will permit real-time control of the sewer system. LOT ends at the upstream end of the OARS tunnel at Neil Avenue and Vine Street. The OARS tunnel performs similar functions throughout downtown, ending at the Jackson Pike Wastewater Treatment Plant.
Surge controls, system ventilation control, and odor controls will be required to coordinate with the OARS facilities. A gated outlet on LOT is also being evaluated to control the system’s fill and dewatering and maximize system storage. A potential innovation will be to dewater the OARS tunnel while keeping LOT full and then using the LOT flow to clean out the OARS tunnel at the end of each rain event.