On a weekend, an accidental discharge of pig fat occurred at the point of rainwater discharge from an animal feed manufacturing plant. The discharge was noted by the operator on the following Monday. A deposit was visible in the ditch over a length of 5-6m; the fat had been retained by the vegetation.
The fat apparently started from a tank leaking into the rainwater network via its passage through a rainwater valve, after fat melting by pressure washer cleaning with hot water, to a lifting station, called a buffer tank, located upstream of the stormwater basin. After passing through the stormwater basin of 700m³ capacity, the fat apparently then went into the hydrocarbon separator and then into the pipeline of diameter 1m collecting all the rainwater from the site and from part of the district to be finally discharged into the ditch before reaching La Canche river. The presence of this valve can be explained by the fact that the area was, in the past, not a transfer area, which explains its direct connection to the rainwater network. This valve was known to the technicians, and was deliberately placed in a position to allow flow to the rainwater network due to heavy rain on the day of the leak on the tank. Moreover, the fat retaining filter at the level of the stormwater basin was inoperative.
The operator:
- performed all the appropriate cleaning operations;
- inspected the hydrocarbon separator at the basin exit;
- undertook daily analyses of the rainwater discharge;
- cleaned the pipeline of the neighbouring firm;
- locked the valve allowing switching of water flow towards the wastewater treatment plant or the rainwater network;
- checked whether other identical situations could arise.
Furthermore, the Classified Facilities Inspectorate asked the operator to provide the necessary retention systems for storage in the various tanks (fat, phosphoric acid, etc.) and the transfer area.
