Wastewater from an industrial park was discharged for 36 hours into the GREE canal after shutting down a lift station at the municipal water treatment plant. This discharge, evaluated at 4,500 m³, 7,200 kg of COD and 430 kg of BOD5, was responsible for extensive fish mortality (the placement of gratings served to recover 400 kg of dead fish). Notified by a local resident, the site operator remarked the lift station malfunction and manually activated the set of pumps. A battle was waged to contain the spread of pollution:

• 10,000 m³ of drinking water were poured into the canal to create a current and refresh the polluted water by dilution;
• a pump (60 m³/h) was installed upstream of the discharge point into the LOIRE on the brook inlet, in order to transfer a portion of the polluted water to the treatment plant;
• lastly, a controlled discharge point was created around the LOIRE, with canal water being diluted by discharging thick flows from the drinking water plant.

After 48 hours, the canal water had been completely renewed, with only a few bands of grease remaining around the rainwater outlet; these were subsequently eliminated by vigorous flushing.

This accident was caused by a malfunctioning piezometric probe that tripped start-up of the discharge station pumps. The particular sensor, driven by the various materials, had been blocked at 0.726 m (threshold value = 0.75 m). Moreover, the safety bulb used to identify an overflow level of effluents in the station was inoperable since the connection cable had been severed.

To reduce the probability of a repeat accident of this type, the following were installed:

• an automated mechanism to revert to operations with level bulbs,
• a 2nd overflow bulb in the 2nd station compartment,
• a piezometric probe failure detection module,
• a junction box located outside the station to avoid corrosion risks.

The operator also recommended setting up a 4,000-m³ buffer tank around the lift station’s overflow outlet and installing an electric generating set.