Sewer rehabilitation projects address overflows by reducing the extent of peak wet weather flows in the system through the identification and repair of defective components of the sewer system and sources of rainfall-derived infiltration and inflow (RDII), such as broken manhole covers or cracks in pipes. Each area targeted for rehabilitation will be assessed to determine the level and extent of repairs necessary to achieve the goals established by the Clean Water Nashville Overflow Abatement Program. The optimal sewer rehabilitation approach may differ from one project area to another and is dependent upon the condition of the existing sewer and other factors.
In many areas, comprehensive evaluation and rehabilitation will be conducted to repair main sewer pipes, manholes, and laterals within Metro’s rights-of-way and easements with the goals of reducing RDII and renewing existing infrastructure. Where possible, the construction of these improvements will consist of trenchless techniques that minimize excavation and disruption to the surrounding community.
Pipe conveyance improvement projects will address overflows by improving the system’s ability to carry increased volumes of wastewater to treatment plants or to downstream equalization facilities. These projects may include the installation of larger pipes or the construction of parallel pipes to handle both existing and future peak flows.
Equalization Facilities offer a means of addressing wet weather overflows by temporarily storing peak flows in excess of the downstream sewer or treatment capacity. The peak flows are stored until the flows in the system recede and the stored volume can be conveyed through the system for treatment. These facilities, which typically consist of a diversion structure, a pumping station, and pre-stressed or cast-in-place concrete structures, may be constructed within the sewer system, at pump stations, or at treatment plants.
Pump station improvement projects will address overflows by improving a pump station’s ability to carry increased volumes of wastewater to treatment plants or to downstream facilities. These projects may include modifications to an existing pump station or the construction of a new pump station to handle existing and future peak flows.
In addition to rehabilitation, conveyance, pump station, and equalization facility projects, additional types of projects may be needed to address specific issues leading to SSOs, CSOs, or water quality impacts. These projects may include modifications to the treatment plants, replacement of screening facilities, or other improvements to the collection system.