Leachate was accidentally released from a treatment tank in a non-hazardous waste treatment and disposal centre. The volume of the spill was evaluated at 30 m³, 2 m³ of which had flowed outside the retention basin. The rainwater outlet valve on this retention basin had been open at the time. Security personnel had detected the leak at around 4:00 a.m. while performing rounds and then alerted the on-call staff. At approximately 4:30 a.m., the retention basin’s stormwater outlet valve was closed, although the retention basin’s water discharge valve to the storage basin was open. A hole in the tank was temporarily plugged with a wooden plug and caulking. Two days later, the operator excavated the soil in the contaminated area and placed it in a storage cell. The volume of contaminated soil weighed 1.88 t. The final operations to repair the leak were performed nine days later.

A crack, measuring 15 mm in diameter, had appeared on one of the tanks used in the biological treatment of leachate. At the same time, following a period of rainfall, the clean water discharge valve in the treatment tanks’ retention area was opened. It should then have been closed, but this was not the case.

Following the accident, the operator undertook the following measures:

• updating of the technical instructions relating to the management of the valves in the retention area;
• a daily check of the status of the valves in the retention area was added to the checklist of elements to be checked on the leachate treatment unit on a daily basis;
• during the operations meeting, all staff were reminded of the role played by the retention area valves and how they are managed throughout the site.