The Austerlitz basin, a key device for making the Seine swimmable, was inaugurated

The dimensions of the work are staggering. More than thirty meters deep and fifty meters in diameter. At the foot of the dizzying staircase that leads to the bottom of the pool, the feeling of being crushed by the volume above our heads. The smell of fresh concrete hits the nose; the echo, at the slightest noise, reverberates on the walls. The twenty columns, which anchor the cylinder fifty meters into the ground and support the slab as a cover for the mastodon, give it the appearance of a cathedral.

After forty-two months of work, for a budget of 90 million euros, the Austerlitz underground pool, located in the 13th^e district of Paris, was inaugurated on Thursday 2 May by Anne Hidalogo. Inauguration where the Mayor of Paris and the Minister of Sports and the Olympic and Paralympic Games, Amélie Oudéa-Castéra, paid tribute to Amara Dioumassy, ​​​​a worker who died on the construction site in the summer of 2023 – the only accidental death recorded today on the Olympic construction sites.

Wedged between the Austerlitz station and the Pitié Salpêtrière hospital, the structure must be put into use by the end of May, after a testing phase. It is a model of civil engineering in a very dense urban environment. A tunnel measuring 2.50 mi in circumference was dug under metro line 10 and RER C, then under the Seine, to connect the basin to two wastewater collection wells located on either side of the river.

With a capacity of 50,000 m³ – the equivalent of 20 Olympic swimming pools – the pool must store, in heavy downpours, parts of the waste and rainwater like the capital’s old sewer network – which dates from the mid-19th century.^e century – discharge to the Seine once saturated. Before the collected volume is returned to the sewer, using a pumping system, as soon as the sanitation system is able to process it.

A plan started in 2015

The Austerlitz basin is the trump card of public authorities (Paris City Hall, State, public authorities bordering the river) to improve the quality of water in the Seine. If it does not guarantee 100% holding of marathon swimming, triathlon and paratriathlon in the Seine this summer, it is part of the longer-term swimming plan than the city of Paris and the state committed in 2015 to improve the water quality of the Seine and make the river swimmable from 2025, after more than a hundred years of prohibition.

Every year, on average, a dozen sewage “discharges” are carried out in the capital’s river during severe weather, for a total volume of 2 million m.³ of wastewater spilled – compared to 20 million m³ thirty years ago. Once the pool is put into use, there will only be two releases per year, assures Paris City Hall, the main financier of the project. Only the most violent rainy episodes will not be able to be absorbed.

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