Tuesday, September 10, 2024
2:00 PM - 2:30 PM
Location Name
Innovative Approach to Inspection of A 4-mile Long CSO Tunnel, 200 feet Underground

Louisville and Jefferson County Metropolitan Sewer District (MSD) was posed with the challenge of preventing an average of 439 million gallons (MG) of combined sewer overflow (CSO) from entering local waterways in a typical year, within urban downtown Louisville, Kentucky. To minimize disruption to local businesses and stakeholders, while preserving real estate values, Louisville MSD elected to incorporate a deep rock tunnel solution. Thus a 4-mile-long Waterway Protection Tunnel (WPT) was constructed 200-ft below downtown Louisville. Since its completion in June 2022, the WPT system has captured over 500 MG of CSO within the first 16 months of its operation. Pumped from the tunnel using a 50-MGD submersible pump station, and conveyed to the Morris Forman Water Quality Treatment Center, treated water is discharged to the Ohio River. This infrastructure has a critical role in providing safe, clean waterways to the Louisville community and its residents. To inspect this WPT CSO tunnel, four options were evaluated: • Manned Entry – In addition to requiring sanitation, this option had the highest risk for personnel and would require heavy machinery to remove the shaft’s 48-ft diameter concrete cover. Subsequently, it was also the most expensive option. • Unmanned Aerial Vehicles (UAV) or drones – While no personnel tunnel entry was the objective, it was learned that radio frequency used to communicate between the controller and UAV will be absorbed by the tunnel’s concrete liner, thus severing drone contact around tunnel alignment curves. Either the drone controller had to walk in proximity to the UAV, or several repeaters had to be strategically placed to always maintain drone communication. • Remotely Operated Vehicle (ROV) – This option would either use an all-wheel-drive rubber-tire ROV or a tracked ROV. Concern with this option was the ROV getting stuck or unable to proceed due to debris or grit within the tunnel invert. • Submersible ROV – This option was the one utilized wherein Louisville MSD filled the entire tunnel, and a submersible ROV, ballasted to be neutrally buoyant in fresh water was used to inspect the tunnel. The presentation will detail technological, logistical, and scheduling challenges that were overcome to plan this inspection, fill the tunnel, and time the inspection just right, to not disrupt the tunnel system’s main functionality of capturing CSOs. Various equipment types mounted on the ROV will be discussed, including multi-beam profiling and imaging sonar, high-resolution camera, inertial navigation system, hydrophone, and non-destructive testing (NDT) of the concrete liner, along with results of the tunnel condition and invert sediment build-up. With poor visibility through the murky water, 2D sonar was used to navigate the ROV, using five propel thrusters. The entire operation was successfully completed in one week, including setup and inspection.