At around 3 a.m., in an aeronautical plant, a malfunction on the soda injection system on the effluent neutralisation unit led to 4 m³ of soda being discharged into the neutralisation basin. The increase in pH in the basin required an increase in the flow of water from the gas scrubbers to the neutralisation basin. Given the large amount of water to be processed and its high pH, the effluents were confined in a basin as provided for in the site procedure. The knife-gate valve on the first containment basin began to leak. The operator installed an inflatable bladder to contain the effluents and the effluent was transferred to a second containment basin. It was determined that the valve between these two basins was also leaking so a new bladder was installed between them. Five-hundred litres of effluents then spilled across 35 m, into a shallow pit (10 cm). An elevated conduit at the end of this section prevented the flow from moving downstream. The operator pumped and processed the effluents.

The soda leak was caused by a broken gasket on a system flange and the malfunction of a solenoid valve which should have closed the system. Crystals may have been formed at this valve. The technicians in charge of monitoring the neutralisation unit were slow to react. The operator had not provided a quick reference card to manage this type of situation. The leaks on the knife-gate valves might be related to a design defect.

The facility operator increased the inspections performed on its soda network, by planning to install new inspection hatches to facilitate valve inspections. A periodic valve check was included in the maintenance program and the system was scheduled to be cleaned. The solenoid valve was replaced. The control systems were reinforced with a system designed to control soda consumption associated with an alarm and the implementation of a system to report the acid storage level. A quick reference card was developed to describe the course of action to be adopted in the event the solenoid valve does not close. The procedure and the associated programming of the PLC to trigger the injection of effluents at a high flow rate into the neutralisation basin in the case of high pH was modified. The knife-gate valves were replaced by inflatable bladders. The technicians in charge of manoeuvring these elements were provided with training.