Construction on our most recent large-diameter pipe rehabilitation project began the last week of October. Insituform Technologies LLC was awarded the contract to renew 1.1 miles of aging sewer pipes along Broadway Street and Riverfront Park. This $2.08-million project is expected to be completed before March 1.
Project Overview
The pipes being rehabilitated serve the southwest portion of North Little Rock, including two large industrial consumers. They are some of the largest pipes in our system with a diameter of 30 inches, or 2.5 feet. Sewer pipes larger than 24 inches in diameter are called “interceptors.” These interceptors range from 13 to 25 feet underground and pass under a state highway, a railroad track, two bridges, and a seawall.
The interceptors are being rehabilitated using Cured-in-Place Pipe, or CIPP. The concept behind CIPP is simple: a tube of felt liner is soaked with resin, inserted into the existing pipe, then cured with hot water, steam, or UV light. The result is a solid, joint-free pipe liner that sits just inside the old pipe, as shown in the photograph below from RJN Group. In this project, the liner will be cured with hot water.
Insituform has a video demonstrating the CIPP installation process.
The interceptors in this area were installed around 1970, when it was standard to use short clay or concrete pipe sections connected at joints. CIPP is jointless, thus alleviating problems caused by joint degradation, such as groundwater and sediment infiltration. Its smoother surface improves the flow of wastewater, and it protects concrete pipes, which become highly susceptible to degradation by wastewater after about 40 years. Overall, this project is expected to extend the service life of the interceptors by approximately 50 years.
Wastewater Diversion
The wastewater flow must be diverted using bypass pumping during CIPP installation. While the permanent interceptors are shut down, the wastewater is pumped past the work area via temporary, above‑ground, pressurized pipes.
Temporary above-ground pipes are more vulnerable than permanent underground pipes. To avoid potential problems, the temporary pipes are pressure tested immediately before use, the sewer lines upstream are equipped with sensors to warn of high flow, twice the number of pumps required are kept available, and the temporary pipes are monitored 24/7.
For more than ten years, we have been focusing on improving the sewer system’s reliability and resilience. This project is just one of many such investments. By using our available resources to revitalize aging, critical parts of the system, we provide the greatest possible benefit to our community, our customers, and the environment.