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The Good Sewer: Why Ottawa’s $232-million sewage storage tunnel is both an engineering marvel and an act of contrition

For the past three years, some nine storeys beneath downtown Ottawa, work crews have been tunnelling a solution to one of this city’s oldest problems: sewage.

The combined sewage storage tunnel, the CSST, is designed to hold for treatment sewage-contaminated storm water that would otherwise be discharged into the Ottawa River.

Ottawa has polluted its namesake river grossly, relentlessly, for the better part of two centuries. Billions of litres of raw sewage have been dumped into the water since Bytown was founded in 1826.

The city’s sewage management has been controversial for almost as long. The complex array of pipes and pumps built to ferry Ottawa’s sewage to the river has led to fatal typhoid epidemics, exploding manhole covers, and fetid scandal. Until 1963, when the city’s first sewage treatment plant opened, every litre of waste flushed into Ottawa’s sewer system ended up in the river.

Ottawa’s newest sewer represents its most elaborate act of environmental contrition.

The $232-million CSST is designed to prevent the oldest parts of the city’s sewer system from overflowing into the river during heavy downpours. It can store more than 43 million litres of effluent — about as much as 18 Olympic-sized swimming pools. When the rain subsides, gates in the tunnel can be opened to send that diluted sewage to the city’s main treatment plant before being discharged to the river.

The tunnel, scheduled to go into operation later this year, will dramatically reduce the amount of sewage piped into the Ottawa River in a typical year. Sewage will continue to spill into the waterway during the spring melt, but for the rest of the year, the CSST is expected to protect it during all but the most exceptional storms.

A 6.2-kilometre engineering marvel, the sewage tunnel is built with the precision of a Roman aqueduct. Yet few will ever see it, and if it works as designed, this will be among the last stories you ever read about it.

Such is the fate of a good sewer.

• • •

“I could talk sewers all day,” enthuses Steve Courtland, the city’s senior wastewater and drainage engineer.

For the past decade, Courtland has been thinking about and planning the city’s new sewage tunnel. He’s been working on the project full-time for four years.

Courtland first became interested in sewers and the world beneath our feet as a young engineering student: “I thought it was cool: there’s this whole underground city,” he says. “In Ottawa, it’s not quite the Paris catacombs but there’s a lot of interesting stuff under the city.”

It’s hard to gain a vantage point on this city’s underground. Ottawa’s massive new sewer pipe is off limits to visitors so Courtland and fellow program manager Jennifer Carreira offer an above-ground tour of the tunnel’s west-end storage chamber.

From the surface, the chamber looks like a concrete grain silo built into the ground. Located at the west end of the new sewer system, it’s only a few steps from the western portal of the LRT’s downtown tunnel, east of Pimisi Station.

The two infrastructure projects were so close together that sewer construction had to be carefully co-ordinated with LRT work. “It was comical how close we were working,” says Carreira.

The t-shaped sewage tunnel, which passes twice beneath the LRT, is really two tunnels: one that runs four kilometres from LeBreton Flats to Stanley Park through downtown Ottawa, and another that runs along Kent Street, from Chamberlain Avenue to the Ottawa River. The two tunnels intersect at Slater and Kent.

Courtland helped devise those routes, which make the CSST a multi-purpose piece of infrastructure.

In addition to protecting the Ottawa River, the north-south tunnel will reduce the risk of flooding in low-lying areas of Centretown and the Glebe by giving stormwater a place to collect — rather than back up into basements. The east-west tunnel, which mirrors a major sewer under Wellington Street, also gives the city the ability to conduct repairs on the aging pipe by redirecting its flow into the CSST.

The four-year project, now nearing completion, represents the city’s principal response to the Sewergate scandal.

Sewergate culminated in October 2008 when the city was fined $562,000 for failing to report the spill of 764 million litres of untreated sewage into the Ottawa River. The spill took place over two weeks in 2006 when sewer gates leading to the river jammed after being opened to release overflow during a rainstorm. City workers covered up the problem.

That summer, Petrie Island beach closed for 45 days because of high E. coli counts that, at the time, went unexplained. The cause wasn’t uncovered until May 2008 when a tour guide mentioned the leak to Coun. Bob Monette during his visit to the city’s waste treatment facility. Outraged, Monette made the story public. Three city workers were subsequently fired for their roles in the foul-up.

The controversy gave the issue of sewer overflows political urgency, and funding for the CSST was included in the $250-million Ottawa River Action Plan approved by city council in February 2010.

But Sewergate was not Ottawa’s first nor its most serious sewage scandal.

In January 1911, a typhoid epidemic swept the city, killing 83 people; the following year, a second epidemic erupted, killing another 91 and sickening thousands more.

The transmission of typhoid was well understood at the time: The disease was most often spread through drinking water contaminated by human feces. Ottawa residents were scandalized that such a thing could happen in the nation’s capital, and some MPs demanded that Parliament be moved to Toronto or Winnipeg until the problem was resolved.

Three separate investigations traced the outbreaks to two leaky water intake pipes designed to draw water from the middle of the Ottawa River. Instead, the faulty pipes were taking in water near shore — from areas contaminated by sewage released upstream.

A city engineer was suspended and the medical officer of health resigned in the ensuing public uproar.

Ottawa’s drinking water was treated with foul-tasting ammonia and chlorine to prevent another epidemic while politicians debated how to secure a clean water source. The Ottawa River was then so hopelessly polluted that some favoured piping water in from Lac McGregor or 31-Mile Lake in Quebec, but those championing a water treatment facility ultimately won the day.

The Lemieux Island Water Purification Plant opened in 1932 to much fanfare, including a 24-page special section in the Ottawa Citizen.

Although the city had largely solved its drinking water problem, sewage still poured like a dark waterfall into the Ottawa River.

• • •

Good sewers made big cities livable. In the 19th century, they were the answer to outhouses and cesspools, which could befoul the air, saturate the ground, seep into water wells, and cause outbreaks of cholera and typhoid.

In Ottawa, the original “main sewer” was built in 1875. It emptied into a creek known as the By-Wash (near today’s Rideau Centre) that led to the Rideau River.

Today, Ottawa has almost 3,000 kilometres of sewer pipe that collect wastewater from West Carleton to Cumberland. In most of the city, stormwater is collected separately from sewage-contaminated water. But older sections of the city — including parts of the Glebe, Centretown and Sandy Hill — have more than 100 kilometres of sewer pipe that combine storm and wastewater.

During the spring melt and heavy rainstorms, these combined sewers are inundated, and rather than have them overflow into basements, the city opens gates to the Ottawa River to release the polluted mix. The city experiences dozens of such events every year. In 2017 alone, 1.6 billion litres of diluted sewage went into the river.

The city’s answer to that mess, the CSST, is essentially a giant underground holding tank that stores the polluted water for treatment instead of allowing it to flow into the river. But that simple description belies the complexity of its construction because building a six-kilometre tunnel deep under Ottawa — beneath historic sites, family homes and the LRT, beneath old sewers, a river and a highway — is no small matter.

• • •

The big dig began three years ago at Kent Street and Chamberlain Avenue, south of the Queensway. A 23-metre deep access shaft dug at that location allowed a tunnel-boring machine (TBM) to be lowered into the ground in December 2017.

The TBM is a 350-tonne cylindrical machine torn from the pages of science fiction. Sometimes called a mole, it’s shaped like a giant can and manned by a 10-person crew. “It’s basically a 250-metre long underground factory,” explains Jennifer Carreira.

It can eat through 30 metres of rock a day with a rotating face studded with steel cutting discs. The machine anchors itself to the sidewalls of the tunnel with hydraulic “grippers” that allow hydraulic jacks to apply forward pressure to the cutterhead. Water has to be constantly applied to cool the 28-tonne rock cutter and control the clouds of dust it creates.

The excavated rock — the typical piece is about the size of a soap dish — is moved by conveyer belt to the rear of the machine, where it’s sent by rail to the tunnel entrance and lifted out with a gantry crane.

As the machine advances, it leaves a finished tunnel. Behind the cutterhead is a mechanical arm that lifts precast concrete segments into place to form the tunnel liner. The pieces fit together like an IKEA bookshelf: Each new segment slides onto dowels that protrude from built sections of the tunnel wall. It takes six segments to complete one full ring of the tunnel, three metres in diameter.

Concrete grout is injected though holes in the segments to seal the tunnel, and fill in any holes between the liner and the rock wall. The TBM uses the tunnel it has just built to move forward: Hydraulic jacks push against the concrete liner to advance the machine.

Piloted with a laser-guided steering system, the TBM took eight months to gnaw its way north along Kent Street.

There were several nervous moments, including the day that the boring machine passed over the city’s 50-year-old interceptor outfall sewer under Wellington Street: If the TBM damaged the sewer, it would have spelled disaster for the city since the old pipe — which collects sewage from pipes that previously dumped into the river — is always full and extremely difficult to repair.

The city had a contingency plan if things went wrong, but the boring machine hit its mark. “The difference, barrel to barrel, was under a metre,” Courtland says.

The TBM emerged in the cliffs below the Supreme Court of Canada in August 2018. It was then disassembled and moved to Stanley Park, where it was lowered into a new access shaft to start its journey west.

The boring machine cut a tunnel four metres below the bottom of the Rideau River then turned south beneath Cumberland Street. Operating 24-hours-a-day, seven-days-a-week — often beneath sleeping Ottawa residents — the machine made a hard right turn as it approached Laurier Avenue.

Again, Courtland held his breath. The city’s underground survey revealed a depression in the area’s bedrock — part of an ancient fault line — that was filled with soft soil. That posed a problem for the boring machine, which operates best in full rock. Soft soil can send the machine offline, and sometimes, lead to sinkholes .

Engineers managed the risk by drilling small holes deep into the target area underground. Grout was then pumped down to form a concrete canopy for the boring machine.

“It was like a concrete cover: We didn’t have a problem when we went through there,” says Courtland.

Since it relies exclusively on gravity to move water, the CSST had to be built with maximal precision. The Romans used hand-crafted surveying tools — chorobates and dioptra — to build their aqueducts, which typically fell 1.5 metres for every kilometre.

In Ottawa, tunnellers used gyrocompasses, electronic sensors and a computer-assisted guidance system to navigate the city’s underworld. (GPS doesn’t work deep underground.) It allowed them to better the Romans: The combined sewage storage tunnel falls less than one metre for every kilometre from west to east.

The tunnel’s 0.095 per cent slope means it can operate entirely by gravity without any pumping stations. “That’s the beauty of the project,” says Courtland.

After one year underground, the tunnel boring machine broke through to an access shaft in LeBreton Flats on Sept. 23, 2019. In keeping with tradition, the work crew crawled out of a hatch at the front of the machine to mark the end of its journey. After tunneling four kilometres nine storeys deep and making two underground turns, they had missed the final target by just 10 centimetres.

• • •

With tunneling complete, construction workers are now putting the finishing touches on the CSST’s water storage chambers and its odour control facilities.

Managing odour means controlling the sewer’s airflow. As water fills the sewer, it will displace air, which will be forced into pipes near the top of the capped storage chambers. Industrial fans will draw that displaced air through carbon filtration units before being vented outside.

Ottawa’s history provides graphic examples of what happens when sewer gases are not managed properly.

On May 29, 1929, around noon, the city’s main trunk sewer erupted in a series of explosions. A fire in the sewer travelled five kilometres through the Golden Triangle, Sandy Hill, Vanier and New Edinburgh, causing violent eruptions when the flaming stew mixed with oxygen near the surface.

Twenty-eight manhole covers were blasted into the air, several homes and buildings were damaged, and one woman, 73-year-old Hannah Hayden, was killed when a sewer explosion set fire to her home.

Although subsequent investigations were inconclusive, most blamed the disaster on gasoline and other flammable liquids being dumped into the sewer system.

Incredibly, the same thing happened less than two years later. On the afternoon of Jan. 28, 1931, exploding sewage travelled a similar route under the city. Again, 28 manhole covers were blown into the air, but this time most of the damage was done to the sewer system itself: a feeder sewer collapsed and the main line was so badly damaged that sewage had to be pumped onto the frozen Ottawa River.

Not surprisingly, heads rolled at city hall: The commissioner of public works resigned and the assistant engineer in charge of sewers was suspended. Investigators concluded that Ottawa needed to improve the “dangerous and obsolete” way it vented its sewers, and impose new rules on what went into them.

Ottawa’s new state-of-the-art sewer can be controlled with computers at the main waste water treatment plant. City workers will be able to modulate how much effluent goes into the storage tunnel, which in any event, will be empty most of the time: It is a rainy day piece of infrastructure.

Later this summer, the new tunnel’s gates will be tested and all of its chambers filled to ensure they’re water tight. The system is expected to go into operation after one final flush.

It means Steve Courtland can now imagine the day when the good tunnel will no longer be his full-time job. It’s an idea that leaves him with mixed emotions.

“It’s exciting, but it’s also a little sad,” he says.

Sewage: By The Numbers

1963: The year Ottawa opened a $26-million sewage treatment plant, the city’s first.

764 million: The amount of sewage, in litres, accidentally sent into the Ottawa River in 2006 when a sewer gate was left open after a storm.

1.6 billion: The amount of diluted sewage, in litres, dumped into the Ottawa River in 2017 during heavy rainstorms that overwhelmed the city’s old sewer system.

$562,000: The amount of money the City of Ottawa was fined for failing to report the spill to the province.

174: The number of Ottawa residents killed in 1911 and 1912 by typhoid epidemics triggered by faulty water intake pipes, located downstream from a sewer outfall.

28: The number of manhole covers blown into the air in each of two sewer explosions in Ottawa (1929 and 1931)

Copyright Postmedia Network Inc., 2020

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