In order to develop novel approaches for reducing the after-care of Municipal Solid Waste (MSW) sanitary landfills methods are required with which we can quantify the emission potential present in waste bodies. Currently full-scale experiments are being prepared at three Dutch landfills based on enhanced infiltration by irrigation and leachate recirculation in combination with landfill aeration. The aim is to reduce the emission potential as fast as possible by stimulating the biological degradation of organic matter in the waste body. Since the summer of 2012 a base line monitoring program has been implemented at the three landfills which has resulted in a data set which can be used to quantify the water balance using high frequency measurements of meteorological data and pumped volumes of leachate. A simple landfill-scale water balance model has been developed which links rainfall, evapo-transpiration, infiltration and leachate drainage. This approach provides us with a method which allows us to obtain a quantitative estimate of the probability distribution of flow velocities and the pore volume in the waste body associated with this flowing water. The parameters in this model are obtained using a data assimilation approach, where the complete parameter distributions using a Markov Chain Monte-Carlo approach with the objective to obtain the best fit of measured leachate volumes and solute concentrations.