The goal of the Department’s Sewer Rehabilitation Program (SRP) is to investigate, identify and correct failing sewer infrastructure in order to decrease inflow/infiltration (I/I) of rain water into the system and extend the life of the sewer system assets.
The Brentwood Services Department’s ongoing SRP program dates back to the early nineties. The activities to rehabilitate sewer pipelines and manholes included, line inspections via closed circuit video and point repairs with chemical grouting. However, beginning in 2006, the SRP program was redefined and expanded to fulfill requirements of an Agreed Order issued to both Metro/Nashville Water Services and the City by the Tennessee Department of Environment & Conservation (TDEC). The Order included a Moratorium on new sewer connections until such time reductions in I/I and overflows were significantly reduced. The mandated program included a comprehensive, $30 million dollar Corrective Action Plan (CAP) that extends through the year 2018 and beyond at a lesser financial committment and is aimed at eliminating sewer overflows by reducing the amount of storm water infiltration and inflow, or I/I, into the sewer system. This is accomplished by increasing pumping capacity at the Brentwood/Metro Sewer Pump Station, pipeline and manhole rehabilitation and repairs up to a point of diminishing returns, and then sizing equalization storage to manage remaining I/I up to the 2yr./24 hour design storm objectives of TDEC.
The programs approach is to identify problematic areas and prioritize rehabilitation tasks through system flow monitoring and video inspection. Projects to be completed by private contractors during the multi-year program include, upgrade of the B/MPS to meet a firm capacity of 9.5 mgd pump rate, rehabilitation of approximately 100,000+ feet of sewer lines and manholes primarily by relining methods and repair found customer service lines by "digup" method or relining when possible.
Pipe “relining” was selected as the primary rehabilitation method because of its minimal impact to above ground property. Pipe lining is mostly a trenchless process and therefore less destructive to the surrounding above ground property. The contractor installs a felt or fiberglass based liner through an existing manhole and into the underground pipeline that is being rehabilitated. Air is typically then applied to inflate the liner and then the liner is cured via ultraviolet light or hot water. Once cured in place, the new liner seals up all cracks and points of infiltration and future surface or ground water is prevented from entering the section that has been rehabilitated. The rehabilitated pipe then has a new life expectancy of approximately 50 years.
Through 2018, the aggressive efforts have had very good success with the department removed from the system a measured 700+ million gallons per year (-2.0 million gallons per day) of rain water I/I, resulting in a reduction of sewer system overflows by about 90%, reducing operational cost of over $1.0 million dollars annually and increasing the life of the system infrastructure for future sustainability. Beginning in 2019, the City secured the engineering services of BARGE Solutions, Inc. of Nashville, to provide continued rehabilitation program assistance at a much less aggressive schedule than was completed under the original CAP. Program efforts will continue to evaluate system I/I increases in areas not previously evaluated and prepare rehabilitation plans accordingly. In September, 2014 the below Program Report was prepared by CH2M Hill Engineers and submitted to, and approved by the State's Department of Environment and Conservation (TDEC), which outlines the City's progress to date and the next phase of work to be completed. Highlights of the work to date are also included.