Pollution
Humain
Environnement
Economique

In a chemical plant, a technician was alerted by an odour and at 7 am detected a leak on a storage tank, before incineration of alkaline wash water loaded with dinitrotoluene (DNT) and trinitrocresols. Manual closing of a quarter-turn valve on a DN25 tap stopped the leak that had lasted over 11 hours. However, about 25 m³ of effluent spilled into the non-watertight retention basin due to repair works, and some areas were severely degraded by jackhammers.

Pumping of the liquid into the retention basin and an external technical duct enabled 13 m³ of residual effluent to be collected; 36 kg of DNT and 180 kg of trinitrocresols had thus potentially infiltrated the soil and/or water table.

To limit the spread of pollution, the operator had to carry out analytical monitoring on a downstream piezometer and ensure a maximum pumping rate at downstream wells to reduce as best as possible any pollution; the contaminated soil would have to be excavated and the construction site covered during the works to prevent stormwater from percolating.

Opening of the manual valve that caused the leak had not been explained; it might have been accidental due to passage of a technician catching the wheel handle of the valve with the equipment transported, with the leak delayed due to the presence of a DNT plug on the tap. Also, work on the retention tank formed part of an intervention plan compliant with the Labour Code (toxic risk to workers), without a preliminary risk analysis on the environment, even though an important safety feature had been rendered inoperable because of this work.

In compliance with the experience feedback, the operator had to establish a procedure for the preliminary identification of potential risks with respect to the environment during works, with a risk analysis and any compensatory measures to be implemented.