How climate change could affect our contaminated soils and groundwater tables: example of light petroleum contaminants (LNAPLs)

International audienceUnder the effect of climate change and human activities, the pressure exerted on water resources increases. In the same time, numerous contaminants’ spills have greatly affected the long-term quality of soils and groundwater tables, making them unusable for decades (IPCC, 2021). However, to improve the management of these contaminations and limit their environmental impact, a better understanding of the factors controlling the (re)mobilization of these pollutants in soils and groundwater is needed. Particularly, the effects of seasonal variations in groundwater levels, precipitation regime or temperature on contaminants’ behaviour must be better considered, especially since these parameters risk to be drastically impacted by climate change and the ensuing more frequent extreme climatic events. For example, previous studies showed that groundwater seasonal level variations may strongly influence the release in soil and water of light liquids petroleum contaminants that float at the top of groundwater (LNAPLs, ex: gasoil). Increasing temperatures could also favour the volatilization and solubilization of these most mobile contaminants and modify their ability to be naturally biodegrade (Cavelan et al., 2022). A better estimate of these climate-related parameters on the remobilization of these contaminants is therefore essential. To this end, two instrumented lysimetric columns allowing the monitoring of contaminated soils under various and controlled climatic conditions were developed at the GISFI station (Homécourt, France). These instrumentations permit the monitoring of the physical-chemical and geophysical properties of the soil (pH, water content, temperature, electrical conductivity and permittivity), and the chemical composition of water and gases emitted at the ground surface (GC/MS, µGC, DOC). In this example, the effect of the intensity of the groundwater level fluctuations and different precipitation regimes on the fate of diesel contaminated soils was tested. The 120 days of monitoring demonstrated that an increase in the groundwater level variation intensity accentuated the spreading and the trapping of the contaminants across the soil porosity, favorizing LNAPL volatilization processes and therefore, increasing toxic gaseous surface emissions. The impact on LNAPL dissolution processes resulting from the weathering of the pure and residual LNAPL phase by rainfall and groundwater level variation events was however limited during these first climatic scenarios, or at least, compensated by the biological activity which have degraded a large part of the contaminants dissolved in the water table.This work is partly funded by the DEEPSURF project "Lorraine Université d’Excellence", ANR-15-IDEX-04-LUE" and is included in the scientific program of the GISFI research consortium (Groupement d'Intérêt Scientifique sur les Friches Industrielles - http://www.gisfi.univ-lorraine.fr