ED Sciences et environnements
Multi-scale characterization, innovative monitoring, and optimization of LNAPL remediation strategies in heterogeneous porous media
by Radjiv BEWI KOMESSE (Environnements et Paléoenvironnements Océaniques et Continentaux)
The defense will take place at 14h00 - Auditorium ENSEGID, Allée Fernand Daguin, 33600 Pessac
in front of the jury composed of
- Olivier ATTEIA - Professeur des universités - Université de Bordeaux - Directeur de these
- Mariem KACEM - Maîtresse de conférences - Centrale Lyon-ENISE - Rapporteur
- Yves MEHEUST - Maître de conférences - Géosciences Rennes - Examinateur
- Antonio RODRíGUEZ DE CASTRO - Directeur de recherche - I2M - UMR CNRS 5295 - CoDirecteur de these
- Irina PANFILOVA - Professeur des universités - École Nationale Supérieure de Géologie (ENSG) - Examinateur
- Dorian DAVARZANI - Ingénieur de recherche - BRGM - Rapporteur
Light non-aqueous phase liquids (LNAPLs), such as gasoline, diesel, and kerosene, widely used in industry, are a persistent source of soil and groundwater contamination, mainly caused by tank leaks or accidental spills. Their complex behavior in porous media, governed by geological heterogeneity, fluid properties, and groundwater table fluctuations, makes remediation particularly challenging. Conventional techniques (pumping/skimming, multiphase extraction, flushing, etc.) have shown limited efficiency over decades, with rapid recovery asymptotes and treatment times often incompatible with site management goals. In this context, this thesis aims to improve the understanding of LNAPL mobility through detailed soil characterization and to optimize remediation strategies using an integrated approach combining innovative in situ monitoring and hydraulic control. The first part presents a critical review of LNAPL remediation techniques, highlighting key limitations such as capillary trapping in heterogeneous media, the lack of operational criteria for technology transition, uncertainties in LNAPL transmissivity, and the impossibility of complete removal. These constraints underline the need for improved methodological and experimental tools to better assess recovery dynamics and guide treatment selection. The second part proposes a multi-scale soil characterization approach combining 3D X-ray microtomography (µ-CT) and gas chromatography (GC). This method enables direct visualization of hydrocarbon ganglia within the pore space and assessment of their connectivity, size, and trapping, providing critical insights into residual mobility and supporting improved prediction of LNAPL transmissivity. A third major contribution is the development of an in situ monitoring tool based on ultraviolet-induced fluorescence imaging (UVIF). This technique allows rapid, non-destructive spatio-temporal visualization of hydrocarbons during remediation and provides near real-time monitoring of saturation changes, offering a robust means to evaluate and compare treatment efficiency under field conditions. Finally, the thesis presents an in situ pilot test combining xanthan and surfactant injection to enhance LNAPL recovery while controlling the treatment zone. Xanthan ensures hydraulic confinement by limiting preferential flow, while the surfactant mobilizes the free phase by reducing interfacial tension. Monitoring with UVIF and hydraulic measurements demonstrates improved surfactant dispersion and effective control of water inflow, confirming the operational relevance of this approach in heterogeneous media. Overall, this thesis delivers significant scientific, methodological, and operational advances, including improved understanding of LNAPL behavior, innovative tools for characterization and monitoring, and the validation of more effective and controlled remediation strategies for contaminated sites and groundwater protection.