Hydrocarbons from a supermarket gas station spilt into the rainwater system and into the Marne River. Filtering dams were set up, and the drinking water production plant located downstream was shut down for the day while the facility operator closed the isolation valve on its stormwater system. The Inspection authorities for classified facilities conducted 2 inspections of the gas station which confirmed the presence of hydrocarbons in the stormwater networks. A section of the network, not shown on the operator’s plans, was identified as the source of the hydrocarbon flow. The Inspection authorities for classified facilities noted several malfunctions, such as leaks in the plugs and settling tanks and the lack of a formal inspection plan for these installations.

A recent soil survey also revealed soil pollution in the vicinity of the unloading and distribution area. An accidental fuel spill from a delivery truck had occurred 2 months earlier. As a result, the Inspection authorities required the facility operator to conduct additional studies to identify the origin of the pollution and to define emergency measures to contain the pollution. These studies show the presence of a micro-leak on the pipe between the unloading area and the diesel tanks. According to the Inspection authorities for classified facilities, this micro-leak could have persisted for several months and have saturated the hydrocarbon separator. The heavy storms in August would then have allowed these hydrocarbons to be released into the network and then flushed into the Marne River.