In a service station, 2,830 litres of diesel fuel contained in a storage tank leaked through the opening of a faulty level gauge. The soil and groundwater were polluted.

When switching the distribution from the 40 m³ tank over to the 15 m³ tank, one of the 2 manifold valves had not been closed correctly. The submerged pump in the 40 m³ tank detected a drop in pressure and pushed the diesel fuel into the piping. As the valve had not been closed properly, the product was transferred to the 15 m³ tank, which then overflowed through the orifice of its electronic gauge, which itself had not been closed properly. Three days later, the high-level alarm on the electronic gauge was triggered and acknowledged without proper field verification. Weekly low point checks were not conducted. It wasn’t until a stock management procedure a week later that the leak was detected.

The inspection authorities for classified facilities pointed to several causes of the leak:

• the lack of a safety protocol to avoid filling the adjacent tank if a valve of the manifold is faulty or improperly closed,
• acknowledgement of diesel tank level alarms twice without performing any verification or analysis,
• leakage or improper closing of the manifold valve serving the tank,
• incorrect closure of the electronic gauge cap, probably during maintenance,
• the failure of the tank’s overfill-prevention device,
• several non-conformities identified in the periodic inspection report of the facilities had gone uncorrected.

The operator sealed off the tank, the discharge and distribution piping and the manifold valve. The station staff was trained in the proper use of the electronic gauge. A daily check of the level of the stocks was put into place.

The staff excavated 60 t of polluted soil which was then processed on site using the biopile technique. A groundwater monitoring system was set up, and a hydrogeological study was carried out. The groundwater was cleaned up by skimming (pumping).