At around 7:30 a.m., agents at the Port of Paris noticed an orangish fatty film measuring 500 m long and 3 m wide floating on the Seine. They alerted the operators of nearby facilities, nearby town halls, and the firefighters. The operator of the waste treatment plant that had discharged the film shut down its operations and started pumping up the film. The firefighters deployed a containment boom. They finished at around 12:15 p.m. A total of 60 m³ of polluted water was pumped out of the river.

Two days earlier (15 August), a leak had been found on a wash-water buffer tank. The tank had been bypassed (its contents were sent directly to the hazardous waste treatment unit) but its contents had not been emptied. The wash water that flows into the retention basin is regularly pumped into containers. At around 9:00 p.m. on 16 October, the crew leader fitted a hose between the bottom of the tank and the manhole of the site’s collection system in order to transfer the contents to the basin. However, he mistakenly sent the contents of the tank into the storm water drain, which leads directly to the Seine.

The operator plans to prevent access to the storm water system by welding the manhole covers. It also increased the awareness of all its employees by distributing diagrams and explanations of the systems around the site.