Pollution of the Arcachon basin: the network manager defends himself

Heavy rainfall last autumn and winter saturated the sewage system, with rainwater seeping into wastewater pipes and causing overflows into the natural environment at safety basins.

This pollution caused an epidemic of gastroenteritis among consumers of oysters in the Basin, in the middle of the end-of-year holiday season, and production was suspended for a month, much to the dismay of the local industry.

Complaints filed by environmental associations have since led the courts to order the construction of "storm overflows" at the safety basins, in order to channel overflows if they were to recur in the event of heavy rain.

To do this, the Intercommunal Union which manages the networks (Siba) has requested a regulatory modification from the State services, currently under examination, denounced by the associations as a "right to pollute".

"It's an interpretation," replied Yves Foulon, mayor of Arcachon and president of Siba, to the press on Wednesday, for whom the network manager is only responding to the injunctions of the courts.

In principle, any discharge of wastewater into the Basin is excluded, but this has happened twice recently, during the winters of 2020-2021 and 2023-2024, after heavy rains expected to recur according to climate projections.

To prevent further pollution, explains Siba, storm overflows would cause excess wastewater to flow into forest areas, where it would infiltrate far from homes and oyster farming areas... but still into nature, criticize the associations.

If the state gives the green light, these spillways would be built "in three to four months", said Sabine Jeandenand, director of Siba.

At the same time, Yves Foulon announced the creation of a new treatment plant in the north of the Basin, in order to "reduce the hydraulic load" on the current Biganos plant.

Its cost would be 30 million euros, with several tens of millions also having to be invested in rainwater management, in urban areas and upstream.

"In total, we are investing 120 million euros over five years," concluded the mayor of Arcachon, assuring that he wants to return to the objective of zero discharge by this time frame thanks to these investments.