At around 7:30 a.m., brine began leaking while the staff of a pharmaceutical plant were starting their shift. The brine contaminated the industrial water return network. A person saw that the river Vertolaye, which passes through the plant, was an unusual colour and called the firefighters. An employee diverted the cooling water, which is discharged directly into the river during normal operations, to a stormwater pond. The pH and conductivity of the Vertolaye and the Dore, its tributary, were tested. The pH was between 6.5 and 8. No aquatic wildlife was reported to have died along the 3 km downstream of the discharge. The conductivity of the discharge was normal at around 9:00 a.m. Water was once again discharged into the Vertolaye.

A total of 2 t of calcium chloride was discharged into the natural environment. The event occurred during low flow conditions, which was a compounding factor.

The leak was caused by a combination of technical and human failures. At around 3:30 a.m., a reactor was filled with brine for a process. A high conductivity alarm went off on the cooling water network, but it was acknowledged by one of the production floor technicians. A technician from technical services detected a low level in the brine tanks, but did not take any immediate action. A return water valve on a reactor was found to be faulty. The reactor was shut down. The brine tanks were topped up (the level had fallen by 28 cm) before the staff started their shift.

The event highlighted:

• monitoring parameters that had not been revised for many years and were not relevant enough (no conductivity alarm on the cooling water discharge);
• a long tradition of accepting that alarms could go off at all times (the conductivity alarm could go off if a tank was not completely drained in the absence of a significant loss of brine) with the result being that technicians could not easily tell normal operating situations from real emergencies (trivialisation of alarms).

Since the event, the operator plans to:

• define a technical solution to redirect discharges automatically to the stormwater pond if pollution is found in the network;
• monitor abnormal brine losses;
• revise the thresholds of the conductivity alarms on the production floor outlet;
• differentiate and rank alarms on the floor’s alarm control panel;
• create instructions for redirecting discharges to the stormwater pond;
• teach staff about the importance of alarms.