Solvent odours were noticed at a tax filing/processing centre. On 16th August and then again on 30th August, the Classified Facilities Inspectorate was contacted by the occupational physician regarding this matter. At first, no precise origin could be identified, though a nearby paint and varnish plant was suspected. Between the 30th and 31st of August, the origin of these odours was confirmed to be the suspected plant. A solvent leak was detected on a pump lifting infiltration water around underground solvent cisterns for discharge into the network. A defective connection between cisterns caused solvent to escape via a tap and flow into the cistern pit before recovery by the pump. The product in question was a washing solvent containing ethyl acetate, ethanol, methyl ethyl ketone (MEK), isopropanol, isopropyl acetate, and propanol. The entire pumping system was neutralised as of 31st August. Pumped water was placed into containers for treatment at an external centre. The firm tracked evolution of the solvent phase in the pump manholes. This phase ended on 12th September. On 10th September, tax centre employees were once again complaining of suspicious odours, at which point the city’s public works department decided to drain pipelines in a two-step process. On 21st September, during another inspection, no odour was perceptible in the manhole adjacent to the tax centre connection. The municipality informed the Classified Facilities Inspectorate that the tax centre’s wastewater system was noncompliant due to the absence of both a siphon at the network junction and a vent on the internal pipe. On 30th September, the inspectorate conducted a site inspection to confirm the situation. As a precautionary measure, the paint and varnish company was requested to plug the pipeline used as a discharge outfall for the targeted pump.