QPAC’s capabilities to model multi-phase flow and to freely couple additional process calculations have been used to model the sequential construction, operational dewatering, and post-closure resaturation of a GDF. Gas generation from the wastes is simulated and the fate of gases is explored. The mathematical model consists of two distinct, but fully coupled, process models, namely multi-phase flow of water and gas in porous media, and gas generation from the chemical processes associated with the corrosion and degradation of organic wastes. Coupling between the two models is achieved through the gas generation model acting as a source and sink for gas and water respectively, while the rates of waste degradation and corrosion are also a function of the availability of water in and around the wastes.