Waterloo biofilm battle
New Aqua-Pipe liner rectifies low chlorine residuals problem
In Canada, the quality of drinking water that flows from the taps of most households is for the most part taken for granted. While the country has pockets of populations with water quality concerns, Canadians generally regard their drinking water not only as safe, but of a higher quality than other developed nations.
Of course, it hasn’t always been this way. Most Canadians will recall the Walkerton crisis of 2000, when an E.coli contamination put the water management system of one small Ontario community under the national spotlight. The town of around 5,000 saw 2,300 people fall ill and seven die after breakdowns in the local water system. The deadly bacterial outbreak resulted in a public inquiry to identify its causes, compensation to Walkerton residents, and the incarceration of the local public utilities commission manager. A report published by the inquiry estimated the economic impacts of Walkerton to be around $155 million, including spending on bottled water and disinfection equipment, plunging real estate values, fixes to the water system and lost business revenues.
Walkerton also resulted in new legislation to ensure the protection of safe drinking water for Ontarians. Passed in 2002, the Safe Drinking Water Act brought provisions affecting the treatment and distribution of drinking water under one statutory umbrella. Among its key components, the SDWA requires mandatory licensing and accreditation of laboratories that test drinking water; sets standards for drinking water treatment, distribution, quality and testing; and requires mandatory certification for drinking water system operators.
Flushing tried and failed
Although it was 15 years ago, Walkerton is not far from the minds of most Ontario residents, so when an upscale neighbourhood in Waterloo started complaining about the quality of their drinking water, the municipality took quick action to find out what was going on.
The city of around 131,000 sent an operator to take bacterial samples and chlorine residuals from a homeowner who described the water as discoloured. The bacterial samples came out fine but the chlorine residuals were found to be “adverse” (low). A repeat chlorine residuals result a week later at the same location had operational staff at Waterloo searching for solutions to get the chlorine residuals back to normal levels.
The first line of attack was daily spot flushing, followed by a unidirectional flush of the neighbourhood distribution system, which was about four kilometres long and included interconnected streets and courts encompassing about 120 homes. When that didn’t result in any sustainable improvements, the operators tried various configurations of hydraulic manipulation; there were no significant improvements. The next line of attack was swabbing the water main. Although the swabbing did turn the water a dark reddish colour indicating some sediment was being removed from the water main walls, another chlorine residuals test still showed adverse results. Finally, as a last resort, crews then tried running water at low flows on a continuous basis from several hydrants throughout the neighbourhood. While this solution moved the chlorine residuals back up to acceptable levels, it was not feasible or practical as a long-term mitigation measure; a working group was formed to come up with a long term solution to the problem.
The answer was to rehabilitate the pipe using cured-in-place pipe technology. “We decided on a structural liner for two reasons,” said Natasha Glauser, water quality specialist with the City of Waterloo. “One was to give the water main a renewed structural integrity. The water main is around 60 years old and did show signs of corrosion and pocking, but the primary reason for the structural liner was to create an impermeable barrier so that the biofilm was not able to migrate through to our newly-lined water main.”
Glauser noted an important part of the rehab plan was to do a “super chlorination” both before and after the liner was installed, to ensure that the biofilm was completely removed. The super chlorination included the laterals running from the main to each household. The plan was to set up a temporary bypass during the summer while the super chlorination was being done, but in order to commission the temporary main, it had to pass two consecutive water quality tests 24-hours apart. That testing requirement delayed the project into the late fall, putting operations staff in direct contact with a familiar adversary: old man winter.
In the fall of 2013 Ontario experienced an early onset of winter weather, meaning the temporary bypass lines started to freeze. Though cumbersome, the solution was to insulate each above-ground hose running into each household, and to truck in water to charge the bypass, adding more time and cost to the project.
“As soon as we received a call about a frozen hose, essentially no water to the house, we would swap out the hose with one that hadn’t frozen,” said Andrew Miller, project manager with Ferpal, the company that installed the Aqua-Pipe liner from Sanexen. “We insulated the hoses as well to help protect against freezing. It’s certainly not a perfect solution. That’s where our focus on customer service came in to try to tackle that problem as best as we could.”
Other issues cropped up as Ferpal set about digging access pits to reline the 4,082 metres of water main. Several residents complained about the road construction involved in digging the pits. Project managers explained that the access pits, 42 in all, were located at T-junctions to minimize the amount of open-cut excavation.
The relining job itself was fairly straightforward. The NSF- 61-approved Aqua-Pipe liner from Sanexen contains a two-part epoxy resin that is designed for water mains. Along with the biofilm issue, the existing cast-iron main was found after cleaning to be deteriorated, including evidence of a number of circular cracks, according to Ferpal.
Miller said a unique feature of the Aqua-Pipe liner is its ability to be wetted-out on site. “There's no need to load the liner up on a facility and wet it out off-site, and bring it back, completely wet. We do it all on-site, giving us a little more control over the wet-out procedure.” A winch truck pulls the liner into place, at which point it is in injected with epoxy resin. A boiler truck then steam-cures the liner.
Two years after job completion, water quality tests from the City of Waterloo confirm that the CIPP water main rehab was successful in addressing the initial biofilm complaints. Tests done six months after the relining showed “very negligible, low results of biological activity in the neighborhood,” said Glauser, “and our chlorine residuals were in a great range. We were very satisfied with those results.”
More tests run during the summer months showed lower chlorine residuals, as expected during warmer weather, but spot flushing brought them back up. Water quality monitoring in year two revealed the chlorine residuals to be within an acceptable range. “We only had to flush once in 2015 following [a spike in biological activity during the summer] and it was just to get the water moving again. So overall we think that lining this area was very successful,” Glauser said. CUI