On a Friday around 6:30 pm inside an industrial chemical plant, 500 kg of naphthenic acid spilled into the AGOUT River via the storm drain network following a handling error. The technician assigned to drain a container of rainwater in the network mistakenly emptied one of the naphthenic acid containers stored in the same spot. After opening the valve on this other container, he failed to monitor the drainage step, instead leaving the premises to continue preparing the loads necessary for a reaction scheduled to begin early the next Monday. The employee returned to the premises 10 min later, realised his error and closed the container drainage valve, but to no avail as the 500 kg of naphthenic acid had already emptied into the river, whose 60 m³/s flow rate (with speeds of 2-3 m/s) accelerated pollutant dispersion.

Naphthenic acid, which is insoluble and non-hazardous to humans, was classified as an environmental toxin, especially for aquatic organisms. First responders activated a water monitoring plan once the alarm was sounded. The initial analysis, performed at 7 pm, indicated a pH of 6 downstream of the discharge and 7 upstream. Dead fish were observed several km downstream of the discharge, though no direct correlation with the accident could be definitively established. Subsequent to this incident, operating guidelines were modified to include container drainage monitoring and a 2^nd person submitting a form to verify water collection in the retention basins. A study was conducted to appropriately place throughout the plant a series of emergency stop buttons triggering the closure of dam valves as a means of isolating the site’s water networks.