During his daily rounds at approximately 5:30 pm, the operator of a sugar manufacturing plant discovered that a basin collecting effluent from the neighbouring facility was nearly empty, even though it should have contained some 30,000 m³. He observed the presence of an orifice at the bottom of the basin, along with a vortex phenomenon and the sound of rushing water due to the flow of effluent in a cavity beneath the basin bottom. According to the operator, the quantity of effluent still present in the basin was minimal.

The hole that formed was caused by repair work in 2009 that had not been performed in strict accordance with professional code. This repair job failed to adequately seal a basin intended to receive acid water stemming from the adjacent industry. An analysis of this water conducted 2 weeks prior yielded the following values: pH = 4.4, COD = 6,651 mg/l, Na2O = 849 mg/l, and Cl = 520 mg/l. The acid water infiltration beneath the basin created a cavity that collapsed due to the weight of water, causing drainage to the water table. Radar controls, followed by destructive controls, revealed the presence of a 3-meter deep cavity along a multitude of small channels. On 29th April, the classified facilities inspectorate presented the Prefect with a draft order suspending basin operations, which would be signed on 17th May.