A security officer smelled solvent near an underground cistern containing 30 m³ of dimethylacetamide (DMAC). The tank, built without a retention basin, was placed onto a simple concrete slab and closed on 3 sides. When a technician forgot to stop a pump in degraded mode (manual operations, without servo control), solvent continued to be distributed. Since the flow control valve was closed (for an unknown reason), pressure in the circuit rose and a leak occurred on a PVC flange. The DMAC dissolved this flange, and 3 m³ of product spilled into the stormwater collection network, then into the PLESSIS River and LORIENT harbour; 100 m³ of water were required to dilute the product. All PVC flanges were subsequently replaced by stainless steel parts.