A cereals and livestock feed wholesaler discharged 12 m³ of liquid fertiliser (30 % by weight of nitrogen) into stormwater, with subsequent pollution caused to the SARTHE River. Around noon, 2 days later, a fisherman noticing dead fish in the river sounded the alarm. Once informed, the operator acknowledged the presence of liquid fertiliser in the retention pond underneath the 85-m³ storage tank, yet which was loaded with 25 m³. The tank and retention pond were drained into the manure ditch of a neighbouring farm, thus making it possible to recover 13 m³ of fertiliser.

The pollution generated by the current reached the water supply extraction zone serving the Alençon urban area (40,000 population) 2 days later; an order was issued the day before prohibiting all human consumption of water as of July 5, 6:00 pm; this injunction would be lifted on July 7 during the afternoon. Other economic consequences were noted, including: a cheese factory and lemon soda plant suspended their businesses for 24 hours, all economic activity related to Alençon municipal services (restaurants, swimming pools, etc.) had to be limited.

The storage reservoir at the origin of the accident was a former transport cistern dating back to 1972 and purchased by the operator in 2003 to serve as fixed storage for liquid fertiliser. Made of stainless steel, this cistern was not adapted to storing liquid fertiliser and its layout did not allow for a straightforward control of its state of repair. Following the accident, several points of corrosion were identified on the bottom of the tank, with one lying on a generatrix responsible for puncturing over a 3-cm diameter, which actually caused the leak.

Moreover, the absence of a retention seal was known to the operator, given that the origin was a former cereal lorry weighing ditch that had not been designed as impermeable; it had not been equipped with any level detection system or alarm.

Lastly, the rather dense drain network installed in the ground, as a result of the business being built on a former marshland, facilitated the rapid transfer of discharged fertiliser to the stormwater network, which emptied into the SARTHE River.

The adoption of procedures for regular inspections and controls of the fertiliser storage installation, in addition to a strategic review of the alert sequence to be implemented in the case of a leak, will come to fruition in order to reduce the probability that such an accident gets repeated.