As with all infrastructure, everything has a useful life and many pipe segments that make up the City’s wastewater collection system are reaching the end of their useful life. A majority of the system was installed before 1970, and is made of vitrified clay pipe. For that reason, the City has a goal to repair, rehabilitate or replace 1% goal or replace pipe once every 100 years. This translates to approximately 2.56 miles of pipe replaced per year.
The City typically has an annual CIP project to improve the condition of the system utilizing a combination of open-trench point repairs or pipeline replacement and trenchless rehabilitation. Scoping the projects begins by prioritizing the pipes and reviewing the CCTV inspection data. From there, the design team pulls together the bidding documents and issues a request for bids. Once bids are received and the contract is awarded to the lowest responsive bidder, a construction management team manages a contractor who will repair, rehabilitate or replace the pipe and improve the condition to an acceptable level.
In order to determine which pipes should be prioritized for placement on a CIP project, the City uses CCTV video data and Pipeline Assessment Certification Program (PACP) standards. The CIP Project Coordinator works with the Planner/Schedulers to review each pipe’s most current PACP structural and maintenance scores, cleaning frequency, and consequence of failure to determine the most cost effective way to improve the condition and extend the useful life of the sewer main.
Construction Methods The City has employed trenchless rehabilitation systems to maximize the use of the available wastewater capital funds and minimize the construction impact on the community since the late 1990s. Some of the trenchless rehabilitation systems used over the past several years include:
Cured-in-place-pipe (CIPP) lining – this method typically uses a felt liner saturated with resin that is cured using hot water or steam to create a new, seamless pipe within the old pipe.
Spiral wound lining - Spiral wound utilizes steel-reinforced, interlocking PVC profile strips. The spiral wound product is fed through an above ground spool and into a winding machine. As the material is fed through the machine, a smooth PVC pipe is formed within the existing host pipe. The material connects with itself and a locking mechanism is engaged for a water tight seal of the continuous liner. This method can be used for pipes 8” to 200” in diameter.
Fold and Form lining - This method is a type of thermoplastic pipe into a U shape. The pipe is heated, folded then pulled into the host pipe. The pipe is then formed back to a circular shape using heat and pressure to ensure it locks into the host pipe. This method can be used for pipe 4” to 48” in diameter.
The total mileage repaired, rehabilitated, or replaced through capital funds over the past several years is depicted below.
In some cases repairs cannot wait for the annual CIP project and must be addressed in an urgent manner. Wastewater staff are equipped to respond and make emergency repairs through the use of a local contractor or trenchless repair equipment.
Trenchless Spot Liners – Since 2015, City staff has spot lining equipment capable of repairing 6-inch and 8-inch sewer mains using a resin-coated fiberglass patch. To install and fix broken sections of pipe, the City crew will mix a two-part resin and spread it onto the fiberglass fabric which is wrapped around a bladder on a trolley. This trolley, also known packer, has a hole in it to allow a portion of sewer flows to passby while the trolley is situated inside the sewer main. After approximately 90 minutes the resin is cured and the repair is complete. When installed correctly, staff expects a 50 year service life from these spot liners.
To learn more about the system used by City staff, see the Source One Environmental PipePatch website.
On-Call Point Repairs – The City has a contract with a local contractor to provide on-call emergency sewer main point repairs to repair damaged sewer pipelines and manholes utilizing open trench excavation methods. Depending on the urgency, the contractor can respond as soon as two hours after being notified of an issue by City staff.