Around midnight inside a sugar refinery, the cleaning tank for diffusion juice heaters with a 24-m3 capacity overflowed into its concrete liner at night. The liquid spilling into the retention basin was a soda solution composed of 2,000 litres of 50% soda (density: 1.51) diluted in 14,000 litres of hot water.

The spill resulted from the poor setting on the tank’s water supply on-off valve; the tank’s safe level (18 m3) was responsible for controlling this valve, yet during a period of intense freezing the valve was not returned to the closed position.

The volume of solution spilled into the retention basin was estimated at 52 m3, i.e. 25 cm in the lining or the equivalent along with 2 full tank volumes. This solution had thus been composed of 2 m3 of 50% soda (1,500 kg of pure soda) and 50 m3 of water, for a solution at 28 g/l.

Once the incident had been discovered, the employee assigned to chemical cleaning cut the hot water supply by closing the manual valve. Alerted afterwards, the sector supervisor deliberately drained the retention to the stormwater facility’s northern overflow basin, to its maximum level (favourable for dilution) at the time of the incident; this overflow basin was in turn connected to the plant’s basins. The solution’s residence time in the lining prior to drainage did not exceed 90 min, thus limiting infiltration risks through the concrete.

The concrete retention basin, devoid of appropriate protective lining, was heavily damaged, as were the tank supports associated with this basin. The stormwater network also sustained potential deterioration. Environmental impacts remained limited, since the soda solution had been diluted before discharge into the Marne River. Similarly, none of the solution was observed to have infiltrated into the soil.

The classified facilities inspectorate “discovered” the incident a month and a half later during a site inspection visit. The facts and information circulation deficiencies were recorded: unsealed retention basin, mix of incompatible products on a single basin, deliberate discharge of soda into the environment, and lack of real-time administrative agency information. Injunctions and additional prescriptions were proposed to the Prefect in order to adapt the retention basin to the products it was destined to contain, in addition to overseeing operational monitoring for the time required to perform these repairs.

An initial incident had already occurred on this same installation in November 2009 (ARIA 38026).