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 Newsticker
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Mar 03, 2010
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No-dig technology makes sewer replacement easy
The city is using a cost-effective technology that replaces century-old sewer lines, with no excavation required, Roger Bird writes.
OTTAWA — It was an environmental and traffic nightmare waiting to happen, on the heels of a sanitation nightmare that did.
Two years ago, the city's infrastructure department set about replacing manholes along a sewer line deep beneath the west bank of the Rideau River. But a 500-metre section of the line collapsed in the Springhurst Park area south of Lees Avenue and the project was put on hold.
The city's man in charge of replacing it, Rick Legault, says the line was made of clay. "It was beautiful workmanship," he says of the carefully fitted square tiles, "but as brittle as a clay pot." No wonder. It was laid down in 1899.
The collapsed line was repaired in 2009, and then it was time to consider the two kilometres of remaining century-old line.
And that was a challenge. The sewer line that needed fixing included two huge pipes across the Rideau at Strathcona Park, and shoreline pipe that went south under the Queensway, under the Transitway, and under hundreds of metres of river shore parkland.
The engineers contemplated months and months of traffic tie-ups, disruptions to OC Transpo buses, and trees felled in order to dig up and replace pipe seven or eight metres below their roots.
But none of that happened because the city opted for "no-dig trenchless technology," also known as "cured-in-place pipe liner" (CIPP), which inserts a new, flexible resin liner into the old pipe, essentially putting a new modern pipe inside the fragile old one. With no digging.
Sandy Campbell is the project manager for Veolia Environmental Services, contracted for the job by the city. "You can well imagine the complications of excavating a sewer that is 25 feet deep in places, that close to the river ... " he says.
One of the complications is the slew of permits required from federal, provincial and regional departments and agencies. Campbell's counterpart at the city's infrastructure department, Luc Marineau, recites a string of them without even having to check: Parks Canada, Department of Fisheries and Oceans, the Rideau Valley Conservation Authority, Ontario's environment ministry, the National Capital Commission ... .
"You need environmental-impact studies too," Marineau says. "How to prevent flooding upstream, and silting up downstream? What happens to fish habitat? That sort of thing. It takes a long time and adds to the cost too."
The stripped-down cost -- construction only, no legal fees -- would be between $7 million and $9 million, he says, compared to the $2.8-million price for the trenchless technology that avoids the hassle.
Sewer lineman Denis Proulx removes ladders from the manhole to allow for the smooth entry of a new sewer liner.
"Imagine your sock," says Stephen Tristram, part of the team actually doing the job. "You wrap the outside of it with Saran Wrap to make it really waterproof. Then you insert it into a pipe, turning it inside out as you do it, so the waterproofing is on the inside."
The "sock" in real life is nearby at the worksite behind Saint Paul's University, an endless tube of white, synthetic cotton, felt-like material stacked in folds about two metres across. A "Saran Wrap" sheath of thick waterproof vinyl encases it. As the tube is inserted into the old sewer line, it's drenched with a fibreglass-epoxy resin that sticks to the old pipe, later hardening into something that looks like limestone. Hardening requires "cooking" for 15 hours with 80 C water from two on-site boilers mounted on trucks.
Legault has been relining pipe for the city for a long time, and a few years back searched online for a way to replace sewers without excavation. He found a technology -- CIPP -- that European cities had been using for 30 years.
"It costs about 10 per cent of what it would cost to excavate and replace a pipeline," he says.
Putting it all together involves just-in-time delivery of the resin. Two tanker trucks -- they look like the big stainless steel milk collectors on the roads in dairy country -- arrived at the worksite a half-hour ahead of schedule after a trip from the resin factory in Covington, Kentucky.
Drivers Bobbie King and Bill Dorning had left 48 hours before for the trek north. "It's the slickest thing since sliced bread," Dorning says of his cargo. "It saves thousands and thousands of dollars."
And it's durable. Legault says prototypes were tested, but lab staff "just quit" after simulating 50 years of aging because the pipe was still good as new.
Pumping the resin into its final resting place goes slowly. Workers hook up to a nearby hydrant and pump water into the folded-open end of the felt tube tied down over the manhole. It's fed forward on rollers inside a big heated tent and droops down into the manhole. The crew pauses when it's halfway through, to insert the heating lines.
Before the crew could start, they laid a temporary above-ground sewer line stretching from Lees Avenue south to Clegg Street to divert wastewater from the old line. The old line was flushed out with high-pressure water from mobile vacuum-cleaner trucks, and scanned for blockages by a video camera rig on treads, looking like a worse-for-wear Mars Rover.
The camera rig stayed underground, water flowed, and two workers jumped on the bulky bundle of tube to help start it down the manhole.
Two hundred metres away, Veolia's Jon Maull tracked the tricky ("This is the hardest part") job of turning the tube at the bottom of the manhole. He watched on his command truck's video screen and retrieved Rover by remote control so it wouldn't get smothered by the advancing tube. The tube front folded into a twisted smile as it came toward the camera.
"We call it the happy face," said Legault as he dropped in to watch. "When that smile forms, we know the tube has gone in the right way."
Source: The Ottawa Citizen
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