Just 21 miles west of Boston and close to the heart of Middlesex County lies the town of Acton, Massachusetts. Named the 11th “Best Place to Live” among small towns in the United States by Money Magazine in 2015, this small town is doing big things.
Acton Water District, like most cities and water districts across the country, must find a way to renew the water distribution system efficiently and at a cost that allows the District to manage the work within a tight budget. The district services a population of 22,000 people through 106 miles of water mains. Acton’s asset management team knows that the 50- to 60-year-old system needs attention.
Getting it Done
In summer 2017, the Acton Water District issued a request for proposals for the trenchless structural lining of asbestos cement pipe. The Indian Village Water Main Renewal project consisted of five connecting streets. The contract called for the cleaning and structural lining of 10,160 lf of 6-in. water mains. The contract was awarded to Onyx Corp., of Acton, Massachusetts. Onyx partnered with Sanexen Water to use the Class IV Aqua-Pipe structural lining technology.
“Given that 50 percent of our water distribution is made of asbestos cement pipes, using Aqua-Pipe allows us to renew the system rapidly with minimal disruption to residents and local traffic. Using a trenchless solution made sense since we are working in a built-up area and we do not need to up-size the water mains,” says water district manager Chris Allen.
The project was designed by the Acton Water District and Wright-Pierce, an engineering firm of Middleton, Connecticut. The scope was to structurally line 22 sections of water mains on five streets including 145 service connections, which are ¾ in. in diameter, which had to be re-instated from the inside.
The project started in mid-September when the general contractor installed the temporary bypass system and was at work digging small access pits. The temp bypass system, which consisted of 4-in. diameter PVC pipe to assure fire protection on the hydrant side of the street and of 2-in. diameter flexible, NSF 61-certified hose on the other side of the street was laid down, disinfected and tested prior to connecting the users to the temporary system. With this temporary bypass, the residents maintain full water service while the mainline is being renewed.
Pit locations were selected to maximize the use of the pits by lining in multiple directions from the same pit. This careful planning by the Acton Water District and Wright-Pierce kept disruption to a minimum and costs down. Pits are 6 ft wide by 10 ft long and to a depth of 12 in. below the invert of the pipe. With these dimensions, the traffic flow is maintained, and residents continue to have access to their driveways without disruption.
Sanexen Water technicians began the actual pipe renewal process by cleaning the asbestos cement pipes using low pressure water jetting. The removal of grime is required to assure a good contact to the internal pipe surface.
This was followed by plugging each of the 145 service connections, as well as the creation of a map to locate and identify each service connection. Some of the services were found to be non-protruding; therefore Sanexen’s patented LED detection system was employed to detect them after lining. These steps are key to assuring the in-situ re-instatement of the services after lining.
Lining was then performed using the Class IV structural liner Aqua-Pipe. Aqua-Pipe is a composite liner that is pulled-in-place while being impregnated with a 100 percent solids resin. This technology has been used for 18 years in North-America on more than 3 million lf of water mains.
“What we like about this technology, is the ability to re-line AC pipes and re-instate the service connections from inside. Our AC pipes are breaking from the outside so the fully structural class IV liner is necessary,” says Allen.
Liners were pulled into the cleaned host pipe to make sure that the water contact surface of the liner remains inside and protected from handling damage or contamination. Because the Aqua-Pipe technology uses solvent-free and VOC free resins, the installed liner was cured using hot water that was re-circulated until complete reticulation of the resin. At this point, the old asbestos cement pipe has been transformed into a solid stand-alone pipe designed to maintain clean and dependable water flow for at least 50 years. More importantly, the precious drinking water is no longer in contact with asbestos fibers.
Following the lining process, the sections were successfully pressure tested to ensure their proper installation. The pressure test is necessary to assure complete watertightness of the newly installed composite pipe. Only when watertightness is confirmed may the robotic re-instatement of services connections begin.
The re-instatement of service connections was done using a proprietary robotic cutter system that allows the surface operator to re-open each service connection from the inside of the lined pipe without having to excavate at each location. This further minimizes the impact and disturbance in this quiet residential area.
As soon as the work inside the new relined pipe was completed, restoration work began. In each excavation, the newly lined water main was reconnected using new ductile iron pipe and couplings. Fourteen hydrants and 18 valves were also replaced with new appliances, which completed the renewal of the whole system.
After disinfection and testing of the new water main, users were transferred back to the main line and the temporary by-pass was removed.
From mid-September to mid-November, the turn-key project was completed and the water main network is fully operational. For the residents of Acton, this small town in Massachusetts accomplished big things by replacing the water mains in an innovative way.