Pollution
Humain
Environnement
Economique

A transfer pipeline was leaking outside of a retention basin at a chemical plant; 10cu.m of 30% soda lye infiltrated into the ground. The leak occurred following annual shutdown of installations, during which time the operator rinsed out the pipes with soda, in connecting the filter at the head of the pipes to the drinking water network via a hose in order to perform a water thrust. Flow passed via the filter drainage valve, left open after rinsing, and via the automatic drain tap placed on the drinking water intake. The spilled soda lye completely impregnated the embankment underneath the storage cell, over nearly 100sq.m, and was blocked by a layer of compacted clay at the base of the embankment. To limit pollution, drains and a pumping station were set up. The impact of this accident on drinking water supply and groundwater quality was evaluated. The integrity of equipment and facilities affected by the pollution was also verified.

The lack of a consignment procedure relative to the installations, no personnel training for such exceptional operations, the shortcomings in procedural precision and a poor definition of responsibilities regarding soda storage operations all played a role in causing this accident. Moreover, the daily recordings of soda volume in the storage tank indicating a drop in stock did not give rise to any special operational response and therefore did not allow detecting the anomaly. Various measures were introduced, including a storage consignment protocol with identification of valves, drafting of verification procedures and lists for pipe rinsing, assignment of responsibilities, personnel training, elimination of water taps in the transfer zone, and laying concrete over the fine gravel zone.