Pollution
Humain
Environnement
Economique

Environmental protection associations observed traces of hydrocarbons on both banks of the COMBE FAVAS stream over 1 km downstream of an oil depot. No fish mortality was observed. Firefighters and the operator set up three mobile dams made of hay bales. The next morning, this system was enhanced following the rise in depot discharge into the stream (that the operator could not explain). Both water and sludge samples were extracted. The operator commissioned the excavation of 35 m3 of sandy earth polluted along the stream, whose total hydrocarbon concentration reached 1,400 mg/kg; these samples were sent for an energy assessment. The investigative campaign also revealed deeper soil pollution lying between 30 and 60 cm, in the vicinity of the watercourse. A specialised firm pumped the polluted water into the river and into the stormwater network manhole shaft.

The Inspection for Classified Facilities, notified on the evening, found that a leak on the retention basin drainage pipes for 2 tanks lied at the origin of this pollution. The hydrocarbon-charged water infiltrated into the soil, migrated along this collection drain and then connected back with the depot’s stormwater network by means of cracks. During a 2006 inspection visit, the Inspectorate observed that hydrocarbon-charged water had been stagnating in the basin for over 2 months. No special procedure had been defined for basin drainage; it was up to the operators to perform this task should they notice iridescence. The Inspectorate requested the operator to justify the controls carried out prior to draining the retention basins.

Unable to repair the retention drainage pipes without jeopardising the dike bases, the operator permanently closed this drain and was to empty the basin exclusively via the oily water network; a written set of guidelines will serve to translate this measure. All pipes adversely affected as well as the oily water treatment decanter were cleaned. Decanter operations were improved by replacing the hay bale filter by an oil separator at the beginning of 2008. The analyses performed pursuant to this incident indicated a more or less diffuse pollution depending on the various retention basins. The operator eliminated the polluted soil in line with the target of removing 500 mg / kg of pollution, in order to avoid another stormwater network contamination, and will be conducting an impact analysis on aqueous discharges from installations.