The emission potential, which represents the total leachable mass in landfill waste body, is hard to measure directly. Therefore we propose to quantify it by assimilating available measurements. The leachate production rate is influenced by the total water storage in the waste body, while both total chloride mass and total water storage in the waste body influence the chloride concentration in the leachate. Thus assimilating leachate volume and chloride concentration simultaneously will help quantify the uncertainties in emission potential. This study investigated the feasibility of using a particle filter in a concentration-volume coupled travel time distribution model to estimate the emission potential. Leachate production rates and chloride concentrations were assimilated simultaneously by a weakly coupled data assimilation method. The time lag issue in the travel time distribution model was solved by adding a daily model error to cover layer states. The proposed method was tested in synthetic experiments first to investigate the performance. The results show that the uncertainties in chloride mass and waste body total water storage were quantified and reduced. The predictions of chloride concentrations were also improved.