On 26 September 2019, the Normandy Regional Health Agency (ARS) introduced reinforced monitoring of drinking water quality. Priority was given to above-ground drinking water reservoirs located under the smoke plume and near the pollution source, followed by groundwater abstraction points used to produce drinking water, located under and near the plume. These were selected on the basis of their vulnerability to surface pollution. The initial analyses covered a wide range of chemical compounds liable to be found in runoff water.
Sixty-six groundwater abstraction points were identified in the 112 municipalities concerned by the prefectural order of 28 September 2019 on food marketing restrictions for the area affected by the deposition of smoke soot from the fire. These groundwater abstraction points were classified according to their vulnerability to the risks of rapid surface-water infiltration in the event of heavy rainfall.
On the basis of their assessment of the sampling strategy implemented by the Normandy ARS from 26 September, the experts of the Emergency Collective Expert Appraisal Group convened by ANSES proposed a comprehensive surveillance programme that can be adjusted over time according to the results obtained.
This surveillance plan combines continuous monitoring of turbidity at all vulnerable catchment points and monthly analyses using screening methods designed to cover the broadest possible spectrum of chemical compounds. It also includes more specific analyses of organic compounds and metals screened for in foods, such as dioxins and PCBs, hydrocarbon indices and PAHs. Lastly, the experts also recommended monitoring a few "sentinel" abstraction points representative of those in the region.
The experts proposed implementing this surveillance plan until the end of 2019. This comprehensive analysis and monitoring programme can then be adjusted and adapted over time. In particular, this will enable it to take into account other substances that may be identified in other environmental compartments.
If the plan detects any compounds that are not included in the routine quality monitoring of drinking water, it will be necessary to investigate their fate in the treatment system, especially after the chlorination step.
In order to distinguish this contamination of the water resource from any that may have occurred prior to the fire, the experts recommend taking measurements from similar abstraction points located outside the area under the smoke plume, to serve as controls.
More generally, the experts recommend that laboratories accredited for monitoring water quality maintain constant vigilance and inform the ARS of any anomalies found.