The fire brigade and police received an alert that the river Marque was a blue-purplish colour. That evening, they determined that dyes were flowing out of the rainwater overflow of the municipal rainwater network of an industrial area. A municipal worker looked into the incident and determined that the colour came from the sewer outlet of a dye and pigment plant. As the plant was closed for the weekend, the worker deployed a containment boom on the water opposite the outlet and collected samples for analysis. Informed by civil defence authorities, the inspection authorities for classified facilities went to the site a few days later. They conducted a fluorescein dye test which confirmed the connection between the settling pit used for the plant’s wash water and the flow of coloured runoff opposite the sewer outlet.

The following day, the plant operator cut off the discharge to the sewer of water from the facilities used to wash the dye mixing equipment and clean the bottoms of the tanks. It also completely cleaned out its network to remove dye deposits that had built up there over the years. It also sealed off the branch pipe connecting the 2 m³ brick settling pit to the public sanitation system because, due to a design flaw, wash water and storm water from the site were being dumped into it.

After the wash water is pumped into the appropriate pit, it will be sent each week to be treated using the appropriate means. Non-polluted storm water will be dumped directly into the sewer system without passing through the settling pit.