Around 10:40 am, an autoclave intended to impregnate wood opened during a pressure rise and released all its contents, i.e. roughly 40,000 litres of a CCA (Chrome Copper Arsenic) solution diluted to 3.3%. Under this pressure, nearly 1,000 litres entered the storm drain network located 15 m downslope and then the settling tank. This basin, filled due to heavy precipitation, could not retain the additional flow, a portion of which reached the TRIBOULIN River. To contain the basin leak, employees fastened a tarpaulin and board using wood joists and began pumping its contents, with fire-fighters arriving quickly to provide support. Around 4:30 pm, traces of the solution became visible downslope of the settling tank, at the bitumen-sand interface; in all likelihood, it had been contained in the underground drain used by the site operator to collect infiltration water (for re-injection into its process). The contents of stone wells where this infiltration water had been stored were then pumped and placed back into storage. A collection trench and impermeable storage, intended to collect the last seepage, were dug around 6 pm. At 9 the next morning, 10,000 more litres were pumped into this basin, which had been partially filled by precipitation the previous night. In all, 160,000 litres of polluted water were recovered, with a concentration rate not easily determined (due to strong dilution), all of which were reused by the operator.

The inspection authorities for classified facilities noted the facts and proposed imposing emergency measures aimed at preventing fouled water that had entered the soil from continuing to pollute the storm drain network. According to the operator, the autoclave door joint may have created the leak that due to a pressure rise caused the door lock to jam and the door to open; it might have been damaged either by a piece of wood that remained lodged against the joint or during loading of the wood. Since this autoclave’s installation in 1988, the joint had been regularly inspected but never replaced. Inspectors ordered the operator set up an autoclave inspection log, at intervals of less than 18 months, in addition to revising its retention configuration, one side of which could allow water to flow into the storm drain network. Water analyses were conducted on the upstream and downstream piezometers, and then in the infiltration water recovery well.