A third party reported an accumulation of foam in the Gave de Pau, a river in south-western France. The foam came from the wastewater treatment plant (WWTP) of a dairy plant a few kilometres upstream. The foam was less abundant the following day. However, according to an environmental association, releases had been occurring repeatedly for several years. The operator said that the foam was not harmful and pledged to clean up the river’s banks.

The foam was caused by regular failures at the WWTP (chronic problems combined with incidents at several workshops). The WWTP’s flocculation tank had been experiencing problems for the last 3–4 years after operations were transferred from a plant that had closed and the dairy diversified its product portfolio. These problems caused it to regularly exceed its authorised TSS and COD levels. Renovation work was carried out following analyses conducted with a specialist company. However, this work was inadequate. On top of this, the WWTP had been accidentally overloaded the last 15 days. Product had been lost from the milk plant during washing operations and salt had been released from the cheese plant when the new brine facility was commissioned. These incidents created an unusual amount of sludge that was discharged into the Gave de Pau in the form of a coloured, smelly foam. No fish were killed. The WWTP’s effluent was piped 1750 m before reaching the river and was discharged onto a bank of pebbles created after the Gave de Pau’s branch had been moved during the flood of 2016.

Work to clean the Gave de Pau was scheduled for the following day. The inspection authorities for classified facilities sent a letter to the operator and the on-site inspection was brought forward to August. Emergency measures regarding the discharge point and its monitoring will be taken and a formal notice about the chronic problems will be issued.