Pollution
Humain
Environnement
Economique

In a chemical plant, wastewater loaded with toluene diamine (TDA) and intended for incineration seeped into the ground and contaminated the groundwater. The leak was located on the branch pipe of the effluent storage tank piping, upstream of the isolation valve. As the retention basin connected to the storage tank was cracked, almost 40 m³ of 0.66% amino-acid loaded effluents were released into the natural environment. The amount of TDA discharged into the natural environment, estimated at 270 kg at the time of the accident, finally amounted to 30 kg given the amount of product recovered in solid form at the bottom of the tank.

The accident analysis showed that internal corrosion due to excessive acidity in the effluent stored caused a leak in the branch pipe and retention basin. The abnormal acidity of the effluents (pH = 2 instead of 4) was produced by the collection of acid water from the spraying of a hydrochloric acid (HCl) leak that had occurred on a rack a week earlier. After detecting the leak through the storage level measurement transmitted to the control room, the effluents still present in the retention basin and in the tank were pumped to a pit provided by a specialised company. Forced pumping from a well located 90 m downstream of the spreading was also carried out in order to reduce the pollution; the effluent recovered was finally discharged into the DRAC river after dilution, via the site’s cooling waters. Given the speed of the polluted groundwater’s progress (10 m/d), the well was only reached one week after the accident.

The inspection authorities for classified facilities recommended that the Prefect made an order for emergency response measures stipulating the pumping of groundwater via the downstream well at a flow rate of 400 m³/h until resorption of the pollution, a study on the feasibility and relevance of the excavation of the contaminated soil for suitable treatment, analytical monitoring on the contaminated well and on 2 hydraulic piezometers downstream, repair of the storage tank and related retention basin and an impact assessment of the pollution on potential targets outside of the site.