One of the challenges facing water distribution system owners is that – unlike their storm and sanitary sewer counterparts – it is difficult to accurately know the structural condition of a pipe. Decision makers often rely on break history, age and water quality issues to inform their decision-making process.
For this reason, an October 2019 pilot project using the Tomahawk System process in the Pierrefonds-Roxboro borough of Montreal proved beneficial. The Potable Water Main: Clean-Evaluate-Line-Protect pilot project was undertaken by Gilbert Group.
The pilot project came about after several rounds of conversation between the contractor and officials in Montreal. Following a technical presentation on the Tomahawk cleaning, assessment and relining process, an agreement was made to go ahead with the project.
“They decided to use the process as a pilot project, in an area where city officials could get out to see the systems in action, as well as address long-standing discolored water issues for the residents,” says Stephane Joseph, B. A., (Env.), director of business development – infrastructure rehabilitation at Gilbert Group. “What we offered included a structural evaluation with an RFT probe. The City wanted to know what the true structural condition of the pipe was.”
The project took place on Dominique Street, a cul-de-sac with seven residential service connections. The 150-mm cast iron main was installed in 1964 and the project covered the rehabilitation of 64 m of pipe. According to Joseph, the location was selected because it was representative of several sections of the system in terms of materials, age and known issues.
Gilbert Group setup a bypass, which was followed by the Tomahawk cleaning process. The Envirologics Engineering patented process involves cleaning of the pipe using abrasives propelled via a high-volume, low-pressure airstream. The benefits of the setup is that it leaves the host pipe clean and dry and can be immediately followed by lining if needed.
While the contractor could have followed the cleaning with the Tomahawk BluKote lining system, one of the key components of the project was assessing the pipe before lining.
Montreal has many pipes, including dead-ends, with issues. The structural analysis is important because they have a huge inventory of pipe that is more than 50 years old, and are in need of information for asset management.
“They may be starting to have small leaks and red water issues and sometimes they wonder what the true structural condition of the pipe is,” says Joseph. “By knowing what the true structural condition is they can then pick the most appropriate repair method, in time and if needed.”
To complete the evaluation, Gilbert Group used the Envirologics Detective Assessment Probe, which uses remote field eddy current probe technology to assess the entire pipe. In addition to scanning capabilities of the probe, an HD camera on the probe provides visual confirmation of defects in the pipe. The probe is pulled through the pipe via a winch at approximately 5 m per minute.
“This pipe is representative of a lot of the other pipes in that area. It’s the same material, approximate age, and in the similar soil conditions. For them, the review of this structural evaluation could help extrapolate those results to other pipes across their system,” says Joseph. “The results showed no significant structural issues. It was a sound pipe.”
Because the process is done along the inside of the pipe, the asset owner knows the true condition of the pipe for the entire length of the scan vs. an average wall thickness by using above ground technologies.
“What we are doing is providing precise data. The probe travels through the pipe and the report shows how much wall is left (or how much wall is lost). We can also provide clues as to the provenance of the wall thickness loss,” says Joseph. “Is the loss on the external wall or internal wall? If they have aggressive soil sometimes it will be more of the external wall. If they have a non-aggressive soil like sand for example, we may find wall thickness losses mostly from the internal wall. If it is from the internal wall, one layer of BluKote is sufficient to stop corrosion and the overall deterioration of the pipe because of the ‘barrier’ between the water and the iron pipe.”
For this pilot project, since the wall thickness losses were minor and mostly internal, cathodic protection was not necessary. Following the scan, Gilbert Group applied the Tomahawk BluKote, an AWWA Class 1 non-structural liner that meets NSF/ANSI 61 certification for drinking water. An AWWA Class 2 semi-structural liner is currently under development, says Joseph.
The two-part resin is poured into the line at the trailer end and a vacuum truck brings the resin, along with the Distributive Body (DB), through the pipe. The DB is tethered to a winch in the trailer and helps distribute the BluKote evenly throughout the line. Because the system uses the airstream, BluKote also fills pits and joints and evenly wraps around service connections, leaving no exposed iron. Following the application, an adhesion test was completed per ASTM D4541 requirements. The results were that the coating exceeded those requirements.
Prior to the return to service, Gilbert Group disinfected the pipe, leaving Montreal and the residents of Dominique Street with increased flow and pressure and a pipe with at least a 50-year service life. And they are also no longer experiencing discolored water issues.
“We had brown water before the project and now it is almost perfect, 90 to 100 per cent. We would go out of town for a week and would have a brown stain in the toilet when we returned, it has been awful for years,” says Joan Fournier, a resident on Dominique Street. “ We are very happy now; it was well worth it. We have lived here for 40 years.”