This work addresses the challenges associated with reactive transport modeling in environmental applications, such as nuclear waste disposal and geological sequestration of CO \(_2\) . Due to limited experimental studies in long-term scenarios, numerical simulation is crucial. A thorough survey of existing codes reveals mainly two types of numerical approaches for reactive flows: global implicit and sequential or operator splitting approaches. Sequential approaches allow specific programming for hydrological and chemical processes. The objective is to develop a reactive transport package that couples PHREEQC for chemical aspects and DuMu \(^X\) for hydrological aspects. The operator splitting method is implemented in a non-iterative sequential approach and a comprehensive description of the mathematical formulation is presented. The spatial discretization employs a cell-centered finite volume method with an implicit Euler scheme for time discretization. The model has been developed and implemented for both single-phase and two-phase flows. Its efficiency and robustness have been validated through a series of numerical experiments, ranging from single-phase benchmarks to complex two-phase flow scenarios. The methodology has been tested notably in two- and three-dimensional configurations, including high-performance computing, thereby demonstrating its relevance for realistic applications.
