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Coxwell Sanitary Trunk Sewer Bypass

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http://www.thestar.com/News/GTA/article/560515

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If Don Valley pipe collapses, raw sewage would spill into river
Jan 01, 2009 04:30 AM
Comments on this story (7)
John Spears
City Hall Bureau

A huge sewer line buried beneath the Don Valley has cracked, and city officials are scrambling to find out how bad the problem is, and how to fix it.

The pipe, 2.4 metres to 2.7 metres in diameter, carries sewage from 750,000 people, living in an arc from western Scarborough to Downsview. It starts in the Don Valley, and runs beneath Coxwell Ave. to the Ashbridges Bay sewage plant.

At worst, if it were to break or collapse, its contents would spill into the Don River.

On the plus side, there's no current indication of trouble. The cracking, discovered by a robotic camera during routine checks last week, may have been there for years.

Lou Di Gironimo, general manager of Toronto Water, said a series of cracks are visible along a 60-metre section of sewer line, just north of O'Connor Dr. In some cases, one edge of the crack is several centimetres lower than the other.

"We're not seeing a collapse, there's no obstructions, the flow is working fine," Di Gironimo said. Extra monitors have been placed in the sewer to keep a closer eye on how it's working.

The pipe, built about 50 years ago, is steel plate on the outside, with 56 centimetres of concrete inside the steel.

The cracked section appears to have sunk about 15 centimetres from its original position, but Di Gironimo said it's hard to be certain.

What is certain is that the city is taking the cracks seriously.

"Our staff have said it's like seeing a crack in the foundation of your house," said Councillor Glenn De Baeremaeker, who chairs Toronto's public works committee.

"The alarm bells have gone off for the City of Toronto. If this pipe collapses, we would have a catastrophic event on our hands. Because you have more water going through that sewer pipe than is in the Don River."

If the pipe is blocked, it's designed to spill its contents into the Don.

"The Don River, from bank to bank, would be covered with raw human sewage," said De Baeremaeker.

"It would devastate the Don River. Our harbourfront would very quickly get filled up with raw human sewage, and everything else that goes in there."

Di Gironimo said the cracking has occurred just downstream from where four other big sewer pipes converge into the Coxwell sewer. Those sewers service western Scarborough, Don Mills, Downsview and North Toronto, he said.

City staff and outside consultants are now using an array of tools, including sonar and laser equipment, to assess the damage and analyze how stable the ground is around the sewer.

The problem was picked up because Toronto Water's long-term plan is to twin the Coxwell sewer, Di Gironimo said. Assessing the existing sewer was part of the project, and it's tough to do because it can't be shut down and emptied.

"Our recommendation is we need to proceed to work on a bypass route as quickly as we can," he said.

That would involve building a new sewer line 500 to 600 metres long around the damaged area, Di Gironimo said. He couldn't estimate the cost.

De Baeremaeker said it's likely to cost in the tens of millions of dollars to fix the problem.

A report on the status of the sewer and the prospects of fixing it is to be delivered to a meeting of the works committee on Tuesday.
 
There's a map of this thing in the paper. This thing is really deep considering it goes beneath the Don River.
 
There's a map of this thing in the paper. This thing is really deep considering it goes beneath the Don River.

any map online?
 
Mods, thou art capricious. Thy humble servant khristopher has so verily had his subject excised.
 
Sewer fix will take 18 months
Jan 07, 2009 04:30 AM
John Spears
City Hall Bureau

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RICHARD LAUTENS/TORONTO STAR

COXWELL BIG PIPE

Where: Built half a century ago, the pipe runs under Coxwell Ave. south of the Don Valley Parkway, carrying sewage to the Ashbridge's Bay treatment plant.

Capacity: Carries sewage from Downsview, north Toronto, Don Mills and western Scarborough. Liquid volume carried is greater than the Don River.

Worst case? It's designed so spillover flows away from homes, into valley and Don River.

Repairs: Estimated cost of bypass pipe project is $20 million to $30 million.
City plans to build bypass around cracked section so massive pipe can be shut down, inspected

According to engineers, the Coxwell St. Trunk Sewer, which carries the sewage of 750,000 Torontonians, has "failed."

A 60-metre section of the huge sewer, buried about 40 metres beneath Barbara Cres. just north of Coxwell Ave. and O'Connor Dr., is cracked and chipping.

But Lou Di Gironimo, general manager of Toronto Water, says the big question remains unanswered.

"When will it collapse? Nobody can answer that question," Di Gironimo told the city's public works committee yesterday.

The cracks may be many years old. The only way to inspect the sewer is through robots with video and sonar instruments, he said:

"None of that can give us any structural integrity information. ... No one can guarantee me how long it'll last. It could last decades. We don't know"

It will take 18 months and up to $30 million to build 600 metres of sewer to bypass the cracked part.

The good news is that there's no sign yet that the big sewer is leaking sewage outward, or collapsing inward. Its flow – three times the volume of the Don River in dry weather – is unimpeded, carrying the waste from one-third of the city to the Ashbridge's Bay sewage treatment plant.

But Di Gironimo isn't sugar-coating the situation.

"It is a Level 5 condition, which is the worst-case scenario," he said after the committee meeting. "When we get a Level 5, we immediately program it for replacement."

The problem with the Coxwell sewer is that there's no alternative. Toronto Water has been working on a plan since 2006 to bring the city's sewers up to standard, including twinning the Coxwell sewer.

Inspections that are part of that project brought the cracks to light.

But the Coxwell sewer is notoriously hard to inspect. No one has been able to enter it since it was built 50 years ago, because it can't be shut down and emptied. If it is, the sewage spills straight into the Don River and its tributaries through several emergency outlets.

"I can't take it out of service to do the repair," said Di Gironimo. "So we need to look at a bypass option."

It will take until April for engineers to figure out the best route to bypass the cracked section and rejoin the sewer downstream. It will most likely run in an arc westward from the current pipe.

When that emergency work is done, Toronto Water will continue to work on a plan to twin the entire sewer for its five-kilometre length, so in future it will be possible to shut down one pipe to fix the other.

The 2.7-metre pipe has a steel outer casing lined with 56 centimetres of concrete. While the concrete is cracked, the steel appears to be intact because no groundwater can be seen leaking into the sewer, Di Gironimo said.

It's an expensive repair, he acknowledged, but the prospect of one-third of the city's sewage flushing down the Don is daunting.

"The cost of not dealing with this, and having it collapse, is even more significant," he said.

Source
 
Perhaps, if they take it out of service, they can convert it to a DRL?

isn't it already a DRL? people wake up, they relieve themselves and it goes downtown. it's the DRL from hell! the crappiest line in the city! and the service stinks!
 
Why do they have to dig a sewer bypass under Coxwell? See what happened in Guatemala City:

This picture was taken in Guatemala City yesterday after a massive sinkhole, a natural depression that can form when water-saturated soil becomes too heavy for its base, swallowed a three-story building

sinkhole.jpg


A ruptured sewer line is thought to have caused the sinkhole that appeared in Guatemala City in 2007.

The 2010 Guatemala sinkhole could have formed in a similar fashion, Currens said. A burst sanitary or storm sewer may have been slowly saturating the surrounding soil for a long time before tropical storm Agatha added to the inundation.

See Infrastructurist.com article at this link
 

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