An acid spill occurred around 7:30 a.m. in a workshop in a factory manufacturing lead batteries. The discharge resulted in saturation of the on-site wastewater treatment plant (WWTP) and the exceedance of the lead emission limit values for effluents between 11/09 and 18/09.

Immediate handling of the accident

After the release was discovered, the operator halted the ongoing drainage operations in its workshops and the WWTP. The operator calibrated the faulty level probe and checked the other sensors on the acid tanks. Soda was injected into a basin of the WWTP to increase the pH. For the treatment operations, a specialised company handled the processing of the 20 t of acidic water still present in the workshop’s containment facility.

Causes of the accident

The source of the event was attributed to the malfunction of a level sensor on a storage tank. During the night, product spilt from the tank’s overflow into the containment facility. As the containment facility’s shut-off valve was broken, the effluent continued to flow into the site’s sewer system, and then into the WWTP.

After analysing the accident report, the Classified Facilities Installation Authorities found that the site had no internal procedure to deal with a major acid spill entering the WWTP. Furthermore, the station was not equipped with a containment basin to collect and neutralise accidental spills.

Measures taken

The WWTP was gradually put back into service starting on 14/09. The results of the self-monitoring of the site’s releases were compliant as of 21/09 and the broken shut-off valve was repaired on 25/09. The operator also installed a network shut-off device (bladder) in the containment facility. Concerning the organisational aspect, a procedure was drawn up to control the alert and manage a major acid spill at the level of acid storage facility’s containment.