In municipal solid waste landfills operating as bioreactor process, leachate recirculation is the key process for increasing moisture content in order to optimize the waste biodegradation. Given that liquid flows exhibit a complex behaviour in very heterogeneous porous media, in situ monitoring methods are required to assess horizontal leachate injection system. Among the physical measurements available, the authors propose a prompt geophysical investigation using Frequency Domain Electromagnetic Method (FDEM). During leachate injection event, this technique highlights changes in electrical conductivity of the waste deposit cell induced by variations of water content. Measurement procedure and preliminary monitoring results are presented applied to a waste deposit cell operated as a bioreactor. First results suggest that this technique is suitable for a quick assessment of horizontal leachate injection systems at industrial scale.