Paris bets on giant tank to clean the River Seine – 11/13/2023 – Sport

Samuel Colin-Canivez, lead engineer for Paris’ water system, stood in a 100-foot-deep concrete cave as hundreds of construction workers rushed to finish the pharaonic project before next year’s Olympic Games.

Their mission: build a 700-meter tunnel and large storage tank to clean the Seine so that athletes can compete in swimming and triathlon events.

“It’s been a marathon, but we’re in the home stretch,” Colin-Canivez shouted over the noise of workers banging hammers to install a final section of barbed steel to reinforce the concrete beneath the tank’s floor. Construction began almost four years ago and should be completed in the spring, at a cost of €90 million (R$473 million, at current prices).

Located between a 17th-century hospital and busy Austerlitz station, the underground reservoir will have a capacity equivalent to 20 Olympic-size swimming pools and is designed to capture overflow from the French capital’s ancient sewage system during heavy rain.

“The goal is to stop untreated water from being dumped into the river,” Colin-Canivez said.

Currently, about a dozen times a year, the city’s underground sewage tunnels are overloaded and, to prevent street flooding, they release wastewater into the river — including dangerous E. coli bacteria found in toilet flushes.

The new storage tank should help reduce such incidents to just twice a year by holding water during storms and gradually releasing it afterwards.

This is one of five engineering projects the Paris region is undertaking to clean up the Seine and Marne rivers, allowing residents to swim in them again. New water treatment plants, pipes and pumps were also built.

Many residents remain skeptical about swimming in the Seine, and there are no guarantees that Olympics-related cleanups will be effective enough to reduce bacteria levels to a level safe for athletes to compete.

Paris was forced to cancel several test events this summer when laboratory monitoring tests showed that there was too much E. coli in the Seine. Excessive pollution was caused by a period of intense rain. The new tank should help prevent these natural phenomena from harming the water.

But a second set of test events in late August were also canceled, even though there was little rain in the days leading up to them, leaving organizers perplexed about the poor water quality. Further investigation found that a faulty valve had been left open, allowing sewage water to escape, and an automatic monitoring system had failed.

“It was disappointing, but we are confident we can get it right in time for the games,” said Pierre Rabadan, deputy mayor of Paris responsible for sport.

If the water quality is not up to standards, Rabadan said the competitions could be postponed for a few days or a week to allow the water quality to improve – but there is no plan B to hold the swimming competitions elsewhere.

That has put pressure on Colin-Canivez’s builders working underground, as well as others who are working on other parts of the Seine cleanup plan, such as the effort to connect barges docked in the Seine to the sewer system.

Another challenge has been convincing homeowners to carry out costly repairs to fix the approximately 20,000 homes and buildings in Paris and surrounding suburbs that are not properly connected to the sewage system.

“Anything we can do will help,” Colin-Canivez said.

Swimming in the Seine was banned in 1923 due to pollution, but politicians have long promised to bring it back. Former president Jacques Chirac promised to do this when he was mayor of Paris in the 1990s, but failed. Heavy rains regularly brought streams of trash and plastic into the Seine, damaging Paris’ historic artery.

Paris Mayor Anne Hidalgo has pitched the Olympics as a catalyst for opening 20 swimming spots by 2025 in the capital, which has become hotter in summer due to global warming.

“It would have taken us 20 years to clean up without the extra boost and budget from the Olympics,” Rabadan said.

In addition to the swimming events, the Seine will be at the center of the Paris games in ways that critics have warned could be overly ambitious and risky.

A plan to hold the opening ceremony on the river has raised security concerns, with police and military authorities raising concerns about the safety of a parade of around 150 boats with 10,000 athletes, as well as crowds of spectators on the riverbank.

Organizers dismiss these fears and argue that the unique ceremony will showcase the beauty of the capital’s riverside buildings such as the Eiffel Tower, Notre-Dame Cathedral and Les Invalides.

Rabadan defended both the parade and the Sena’s cleanup efforts: “There is no plan B, as executing plan A will be complicated enough.”