Pollution was reported in the Kergoutois downstream of the stormwater pond of an infant formula plant. The inspection authorities for classified facilities went to the scene. A visual inspection of the stream was conducted along 160 m downstream of the plant’s discharge point. The stormwater management and settling pond, the point where this water is discharged to the pipe leading to the stream and the storage area reserved for hazardous products were also inspected. Water samples were collected at various points (upstream/downstream of the stream, the stormwater pond’s outlet, the plant’s discharge point, etc.).

The inspection authorities for classified facilities found the following irregularities:

• a decrease in the quality of the water downstream of the plant’s stormwater pond: unusual odour, fouling, proliferation of algae, wildlife death (slugs), presence of a coloured and fatty supernatant;
• cans labelled as containing environmentally hazardous products were stored on the road without any containment system and along the edge of a slope of several meters without a guardrail;
• significant pollution in the stormwater pond (a sheen and solid matter could be seen on its surface). The water in the pond is fed back to the natural environment by an automatic pumping system.

The operator emptied the stormwater pond that day. It had last been cleaned on 25/05. Seeing that the oil separator was saturated, he reckoned that this may have caused effluent to chronically leach out. The separator was also emptied and cleaned.

The inspection authorities required the operator to immediately:

• halt automatic discharges of effluent pending the cleaning of the pond;
• place containers of hazardous products on containment systems;
• verify compliance with its prohibition on discharges of reverse-osmosis retentate of municipal water to the stream via the stormwater pond.

It also required the operator to:

• analyse the site’s networks to find the source of the pollution in the stormwater pond;
• inspect all the wastewater/stormwater networks and connections to ensure that only stormwater reached the stormwater pond;
• conduct a study to verify the relevance of the stormwater pond’s discharge conditions (flow rate, frequency, etc.), characterise the damage to the stream (location and linear length affected) and propose and quantify the cost of technical measures that may be necessary to rehabilitate the site and/or modify the discharge conditions.