At around 15.30, the operator of a pig farm noticed that the liquid manure reception pit was overflowing. Liquid manure was running into a nearby stream, then the PENZÉ river and the KERJEAN tributary. Since early morning, in preparation for corn sowing, the operator had been spreading liquid manure. He went back and forth, every 15 min, between the liquid manure reception pit and the fields, spreading approximately 100m³/h. The reception pit was collecting liquid manure from another site at the same time. At around 15.30, on returning to the pit, he noticed it was overflowing. He attempted to identify the origin, shut off the liquid manure input from the other site and, in order to lower the level, decided to double the spreading capacity. He also set up a straw filter upstream from the PENZÉ.

The French Biodiversity Agency and 2 certified fishing and aquatic environment protection organisations noticed dead fish along an approximately 1.5km stretch of the PENZÉ river and 1km of the KERJEAN tributary. On the PENZÉ, visible traces of pollution were few and far between but on the KERJAN tributary they were easily visible (odorous, dark deposits on the banks in low-speed runoff zones and on the surface). Among the several hundred dead fish collected or left on the riverbed, dead specimens of the following protected species were recorded: Brook lamprey and trout. Anglers also collected Atlantic salmon.

The volume of liquid manure spilled into the environment was estimated by the operator to be between 50 and 100m³.

The morning of the overflow, work was done to unplug a section of a washing pump pipe under a building using a plumber’s snake. During the work, an in-draught was generated upstream from the pipe, causing the drain U-bend (PVC tube) for the 2 reception pits under the building to move. The volume of excess liquid manure collected in the reception pit was estimated to be 300m³. The PVC pipes used as drain valves for the reception pits were put back in place, halting the transfer to the pit and, as a result, stopping it from overflowing at around 17.00.

Following the event, the operator put in place the following actions:

• installation of a transfer valve between the reception pit and the 2 production sites;
• creation of a retention basin below the liquid manure processing plant;
• performance of a comprehensive runoff risk audit.

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