Hydrocarbons were detected in the stormwater discharge pit of a food processing plant, spilling into the ALZON River. This pollution was discovered around 11:15 am by someone not affiliated with the plant. Emergency services were notified. A pneumatic stopper was installed on the concrete pipe channelling water overflow into the river; moreover, 2 floating dams were implemented both in the pit and on the watercourse.
The operator was able to locate the source of the leak: a pipeline connected to a 3-m³ aboveground tank containing light fuel oil from the fuel oil reserves, where another 70-m³ heavy fuel oil tank was also in service, as was a 3.5-m³ reservoir of domestic fuel oil; a total of 300 litres of fuel oil had spilled from the 1st tank in the pit, a portion of which had reached the river.
The operator stopped the leak on the pipeline by means of plugs and a solid flange and moreover proceeded to pump the polluted water and scour soil sediment in the pit (100 m² of polluted soils – 200 m of riverbanks). Since the Saint-Maximin extraction point for drainage and stormwater was located close by, the authorities requested pumping be ceased for a part of the day; activities resumed at 7 pm after several samples and analyses had indicated the absence of any significant impact from the spill.
A major thunderstorm led to filling the retention basin associated with the fuel oil reserve and automatically triggered the drainage pump on the retention basin, which contained 200 litres of fuel oil originating from the leak subsequently detected on the transfer pipeline.
A series of flaws, in both equipment and organisation (design), were identified; the causal tree indicated a breached seal on the sectional valve of the light fuel oil tank, along with the presence of a leak on the pipeline of the fuel oil mixing circuit and the drainage of retention basin contents via a pump, which had been automatically activated, controlled by a float gauge.
The operator neutralised this automatic pump starter. The fuel oil reserve was to be dismantled over the coming weeks once the site had transitioned to a natural gas supply for the backup boiler.
