The nation's first performance-based contract to rehabilitate a major city's sewer system is underway in Nashville, TN.
Under the terms of the contract, Reynolds Inc. will use a variety of renewal options to eliminate 20 percent of clear water infiltration and inflow (I/I) into the city's sanitary sewer system in the Whites Creek drainage basin on the northwest side of Nashville. The Inliner Technologies method of cured-in-place pipe (CIPP) will be emphasized throughout the project area.
Clear water infiltration typically comes from high ground water, which seeps through defects in the piping network and manhole structures. Inflow comes from more direct sources such as manholes that lie in low areas prone to flooding and via illegal stormwater connections such as downspouts and drains from residences and businesses.
Nashville Metro's wastewater overflow abatement program management firm, Consoer Townsend Envirodyne Engineers Inc. (CTE), is overseeing the project. As the performance-based method had never been tried in the sewer rehab industry, developing the plan was no easy task.
"We spent 13 months setting up the plan," said Vern Thompson, overflow abatement program manager for CTE. "We called on the industry to help come up with an arrangement that would be beneficial to the city, as well as the contracting community."
Nashville Metro Water Services decided that rather than identify the specific sewer lines to be renewed, they would identify a desired outcome and leave the methodology of achieving that outcome up to the contractor. The only specification outlined was a boundary for the 20,000-acre drainage basin in Whites Creek. This basin has experienced limited previous rehabilitation and contains primarily vitrified clay pipes, which are riddled with leaking joints, cracks, and leaking service connections. These two facts made the basin ideal for this sort of contract.
The Reynolds' proposal defined a clear I/I reduction amount and called for reimbursement at "cost" for labor and materials. The proposal led to the current $7.0 million project that calls for 20 percent reduction in I/I over a maximum five-year funding period. The contract allows for a bonus if additional I/I is removed and assesses a penalty if the 20 percent reduction is not achieved.
One of the project's initial challenges was to determine a baseline to measure Reynolds' performance, said David Bible, project manager for consulting engineering firm ARCADIS, subconsultant to Reynolds. This analysis is especially difficult when dealing with increased flows from rain runoff and backups from the pumping station. The Reynolds/ARCADIS team did extensive flow testing and data analysis, then worked with CTE to develop a fair plan.
After the baseline flow was established, Reynolds began system renewal through a find and fix approach, said John Morgan, project manager with Reynolds. "This approach decreases the amount of turnaround time between identifying defects and making necessary repairs; hence it produces noticeable flow reductions more quickly." Individual rehabilitation techniques are evaluated on a case-by-case basis and will focus on Inliner's CIPP. Other methods being used include joint repair, excavation and replacement, part lining, and various manhole renewal alternatives.
Once Reynolds feels confident that the incentive goal has been met, the company will conduct flow monitoring to verify the reductions in flow and project success.
"Key to Reynolds' success will be the fact that they can offer more than just one solution to fix a particular problem; so, under the performance-based nature of this contract, they can give Nashville Metro truly the most cost-effective solution," said Ed Kampbell, vice president and general manager of Inliner Technologies. "This in-house capability was an advantage they had over other lining companies that could offer these other solutions only by subcontract."
