An explosion occurred around 1:00 am in a single-family dwelling. On their return from a trip, the homeowner by drawing hot water from a tap caused the water heater to turn on, causing ignition of the hydrocarbon vapours that had accumulated in the basement when the house was closed. The owner was slightly injured and the house completely destroyed.

Hydrocarbons had been found in the groundwater dating back to 1985; as of 1989, their presence led to the detection of odours in the town. Expert evaluations conducted since 1987 enabled identifying the polluted zone and assigning responsibility to the refinery located 2 km away. A drinking water catchment had to be shut down in 1986 and pumping in the aquifer was already underway prior to the explosion.

On August 23, 1990, a leak was identified at the level of an elbow on an underground line that had been conveying premium grade fuel from the refinery, after having previously transported products of the type containing diesel fractions and turpentine.

According to experts, several factors would have contributed to line corrosion :

  • the ground was composed of clayey fill with many sharp-edged rocks (flint), some of which made an “imprint” into the pipe lining, each time initiating additional corrosion. The pipes sat on steel rods, a configuration that was capable of prematurely deteriorating the pipe lining.
  • earth removed from the site revealed a very weak concentration of chloride along with a considerable presence of phosphate and sulphate ions, which increased soil conductivity
  • the punctured line and its neighbouring lines were influenced by the cathodic protection of lines located in the vicinity, thus increasing the speed of corrosion at those spots where the tube was uncovered.

The surface area of the polluted water table was estimated in 1989 at 100 ha, with the loss of over 15,000 m³ of hydrocarbons and more than 13,000 m³ pumped into the groundwater. The refinery operator settled with all third parties who sustained damages: the owner of the destroyed residence, the water supply distributor, and the municipality. The total cost of compensation paid out plus ancillary works exceeded 50 M francs (in 1991 currency).

Subsequently, a campaign was launched to inform residents, sewer network operators and the various utilities of the risks incurred both adjacent to the pipes and inside underground premises. The operator proceeded with a leak inspection of all tanks containing light products and all underground pipes at the refinery; no other leak was found as a result of this follow-up inspection. The refinery operator decided to reroute all buried pipes aboveground or into ducts feasible for inspection, in addition to allocating the resources necessary to absorb pollution. A BTEX monitoring network was set up to focus on the municipality’s professional premises and residential units. Lastly, the cellars of exposed dwellings were caulked.

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