[en] Full text: Stable isotopes have been routinely used as valuable tools to study the hydrogeological systems and groundwater contamination processes. In other to evaluate groundwater contamination by a landfill leachate plume, hydrogeochemical and isotopic studies were carried out in groundwater around the site. Groundwaters were characterized by high levels of bicarbonates and lesser extent of sulfates, indicating the large amount of carbon dioxide produced by the biodegradation of organic wastes under anoxic environments. Polluted waters have significantly higher levels of dissolved ions than the groundwater aquifer. The Wellslocated in down gradient ofthe landfill andin the direction ofgroundwater floware moreenriched in deuteriumrelative to otherwells,indicatingintenseisotopic reactions with methanegasesproduced bybiodegradation oforganic wastes.Demonstratinggroundwater contaminationbyleachatesplumes. The alkalinityis positively correlatedwiththe isotopic compositionsof deuterium andoxygen-18 in water samples collected fromthestudy area.The isotopic signatureof contaminated watershows a strongenrichmentinD,indicating methane viacarbon dioxide reduction. This study shows thatstable isotopescan be used aspowerful tracers to trace subsurface migration of leachate plumes andmap with precision thepollutionfront.