The municipal stormwater network was polluted by used oils and hydrocarbons stemming from a fuel distribution and freight contracting company, whose premises included a repair workshop and a lorry washing area, located within a narrow protection zone for drinking water catchment.
During its field visit, the Classified Facilities Inspectorate observed an overflow of the single-wall underground tank used for storing used drained oils from vehicles, which was the cause of the flow of pollutants into the stormwater network via ground infiltration. This tank, whose operator was unaware of the exact volume, was apparently quite old and devoid of any level detection (tank saturation could only be assessed visually), as were both of the other tanks located nearby containing clean oils. Additional observations included the presence of several 200-litre barrels of oils stored outside the retention zone; irregularities in the lorry washing area (especially cisterns having once contained products potentially hazardous to the environment) that never gave rise to administrative enquiry; and washing residue flows after hydrocarbon settlement and separation into the sewer network, which might have caused clogging of pipelines according to the city’s public works staff.
A specialised subcontractor was called to clean the manholes and stormwater network, as well as drain the 3 storage tanks. A salting-out of oils most likely infiltrated into the soil was detected. The operator commissioned a specialised body to delimit the polluted zone, characterise the pollution, dispose of the polluted soil (40 tonnes), and analyse both the soils following excavation and groundwater quality downstream of the site. Moreover, the tanks were disassembled and retention capacities installed underneath the barrels capable of causing pollution. An absorbent blanket preventing contamination of the stormwater network by oils (including oil infiltrating into the ground) was kept in working order onsite until conducting the measurements that guaranteed the absence of any new pollution risk.
