Characteristics of pipeline:

  • Diameter: DN 300
  • 40 bar pressure
  • Commissioning year: 1964
  • Depth of burial: 84 cm
  • The pipeline connects the Donges refinery to the Vern-sur-Seiche depot and extends over 93 km
  • Transported fluids: diesel, domestic fuel, gasoline..

When laying an underground power line, a trencher damaged a hydrocarbon pipeline at around 9:30 a.m. A breach in the pipe measuring 20 cm x 30 cm led to 400 m³ of diesel fuel (340 t) to flow into the natural environment, affecting ten or so homes in the hamlet of Tragouët. The facility’s safety and emergency response plan was initiated.

The pumps controlling the pipeline stopped automatically at around 9:45 a.m. and the damaged section was isolated. The emergency services established a security perimeter of 500 m around the leak. Explosivity measurements were conducted. Ten homes (25 people), affected by the pollution, were evacuated. In all, over 80 firefighters were present at the height of the crisis.

Repair of the pipeline

The pipeline was repaired in several phases:

  • installation of a temporary plug to limit the release of VOC (Volatil Organic Compounds) associated with the presence of gasoline in part of the pipeline and the control of product flows;
  • installation of a clogging box to transfer the gasoline still in the structure to the Vern-sur-Seiche depot by pushing the product with diesel fuel;
  • cutting and replacement of the damaged section with a sleeve.

Communication about the accident

A crisis unit was initiated for 10 days. The prefecture also held public meetings to explain the actions undertaken to the residents who had been forced to evacuate. The pipeline operator and the town hall also issued several press releases.

Environmental impact

Private properties, 1 km of ditches and 2 ponds representing 18,000 m², were polluted by the release. The vegetation was also impacted. The consumption of well water was prohibited as a precautionary measure pending the completion of verification measures. The two ponds made it possible to avoid the polluting the NATURA 2000 conservation area only 3 km downstream of the leak.

Absorbent materials and booms were deployed as part of the site’s clean-up operations. Twenty or so lorries were used to pump the spilt fuel and skimmers were used to clean the surface of the ponds. The fouled absorbent materials were recovered in leak-tight containers. The pumped products were taken to the Donges refinery. The ditches were eventually cleaned and the soil evacuated.

The Prefecture appointed several organisations to conduct site surveys and monitoring operations alongside the operator’s crews and government services.

Furthermore, the inspection authorities for Classified Facilities (IIC) requested that the operator set up a health and environmental monitoring system through an additional prefectural order. Surface waters were affected by supernatant and dissolved hydrocarbons resulting in the death of a few dozen kilograms of fish in the ponds. High concentrations of hydrocarbons in certain locations lead to soil pollution. Birds, small mammals and amphibians was also found dead.

Economic and human consequences

Following the evacuation and relocation of residents, a distressed individual was assisted by the emergency services. Some of the residents were able to return to their homes three days after the accident and another group three months later. On 1 September 2016, two homes still remained uninhabitable due to the VOC concentrations in the homes which were attributable to diesel fuel pollution. The overall cost of this leak was evaluated at several million euros.

The transfer of diesel fuel and gasoline between the Donges refinery and the depot in Vern-sur-Seiche was interrupted for nearly a month, the time required to repair the pipeline. This situation led to increased tanker lorry traffic to ensure the supply of fuel.

Deep-rooted causes

The IIC conducted an administrative enquiry among the various parties involved: the public works contractor, contracting authority (electricity provider), pipeline operator. Several points were examined: establishment of the “Déclaration de Projet de Travaux” [DT] (Statement of works project) (contracting authority) / “Déclaration de Commencement de Travaux” [DICT] (Declaration of intent to begin works) (public works company), elements sent by the transporter within the scope of responses to the DT/DICT, identification of the network before works, suitability of the equipment used for the work, etc.

The IIC noted that certain regulations pertaining to the protection of buried networks had not been respected. The judicial inquiry is ongoing.