T2GGM consists of a gas generation model (GGM), which calculates rates of gas generation and water consumption within a deep geologic repository (DGR) due to corrosion and microbial degradation of the waste packages, integrated with the widely used two-phase flow code TOUGH2.

Part of the Eurotom Fate Of Repository GasEs (FORGE) project, the FORGE benchmark modelling examined the transport of gas in a hypothetical repository, with the objective of improving gas migration modelling to support performance assessments at the repository-scale . Nine different groups contributed to the benchmark modelling exercise with different codes and modelling approaches, including Geofirma representing NWMO.