A mathematical model is developed to simulate the hydraulic behaviour and the biodegradation process in a landfill site. The model incorporates governing equations that describe processes influencing the leachate production and the biochemical processes taking place during the stabilisation of organic wastes, including leachate flow, hydrolysis, acidogenic, and methanogenesis. The model considers the significant changes in moisture distribution and leachate quality that may occur during the operational period of the landfill. The model results are compared with the leachate production, chloride concentration, BOD, pH, and methane production data from Keele Valley Landfill in Ontario, Canada. Encouraging agreement has been observed between the real landfill data and the model results.