Seminar Mohamed Boujoudar

Groundwater contamination by pesticides is a major concern in agricultural regions such as the Beauce aquifer in France. In this context, this study investigates the reactive transport of a newly synthesized molecule, derived from the 4-hydroxy-2-pyridone (4H2P) family, with a particular focus on its behavior in the vadose zone.
The approach combines laboratory experiments with numerical modeling. Column transport and batch sorption experiments were conducted to characterize the interaction of the molecule with soil and mineral phases. Breakthrough curves were analyzed using inverse modeling to estimate transport parameters, while adsorption isotherm models were used to determine sorption properties. These parameters were then implemented in numerical simulations to evaluate its migration at both laboratory and field scales.
Transport modeling results indicate a moderate retardation in agricultural soil (R ≈ 3) compared to a conservative tracer (R = 1). Adsorption remains moderate, with a slightly higher affinity for clay minerals, particularly montmorillonite, and is mainly governed by physisorption. Numerical simulations further show faster migration and lower persistence in calcite-rich formations compared to soils.
Field-scale simulations along the vadose zone profile of the O-ZNS observatory, conducted over a 55-year period (1966–2020), indicate that the travel times associated with the first arrival, peak concentration, and disappearance of the molecule at the groundwater table are approximately 30, 34, and 55 years, respectively.
These findings highlight the key role of vadose zone properties in controlling solute migration and emphasize the need to better represent biodegradation, photodegradation, and soil organic matter interactions in future studies.