An abnormal smell of petrol was detected around 9:30 a.m. in an oil depot, although the employees did not identify any leaks. The following day at 3 p.m., petrol odours were again detected. A mini excavator was used to remove slabs and bitumen covering a fuel pipe. The contractors noticed a leak; the concrete gutter was filled with hydrocarbons. The fuel contained in the hose was pumped to a tank. The hose was then filled with water and locked out, while the gutter was drained. A special monitoring system was set up. The operator estimated that 1,300 litres had been released. The contaminated soil was excavated and then stored in a dedicated area.

On 12/11, the leak was located once the pipe had been cleared. A hole was found in the sheet metal along the lower generatrix. A temporary patch was applied on 14/11. On 17/11, a clamp type band was installed after the pipe’s coating had been removed. A specialised company conducted a pressure test on the piping at 4 bar, but no anomalies were detected. Until the piping was replaced in the 1st quarter of 2015, the operator limited utilisation of this equipment to the following:

• usage for tank-to-tank transfer, no usage for unloading ships,
• operating pressure limited to 2 bar, compared to 6.5 bar previously,
• reinforced monitoring by means of a pressure gauge, visual inspection of the clamp and the section, specific monitoring of the 6 nearest piezometers.

The leaky piping (DN 700, steel) was manufactured in 1970. It consisted of welded spiral tubes coated with bituminous pitch on the buried parts. In July 2014, an inspection body detected a loss of thickness on another part of this pipe. Repair of the section was recommended. The facility operator then reduced the operating pressure from 10 to 6.5 bar.

According to the operator, the breakthrough may have been due to internal corrosion of bacterial origin (sulphate-reducing bacteria). Investigations were being conducted to confirm this hypothesis. Plans were made in 2015 to test the techniques for checking the condition of underground sections. In the long term, it plans to render all underground sections accessible by replacing the asphalt of road crossings with grids in order to easily inspect the pipelines.

The inspection authorities for classified facilities visited the site on 24/11. Following the inspection report, the prefecture adopted the following protective measures:

• return to service of the piping after repair was contingent upon prior authorisation by the prefect,
• the facility operator must provide a report indicating the results of its investigations, a plan of preventive and corrective actions taken and the lessons learnt,
• strengthening of monitoring by piezometric wells.