Particle methods for reactive transport modeling in heterogeneous aquifers

Tesi amb menció de Doctorat Internacional (English) Aquifers are naturally heterogeneous systems across multiple scales, which poses a known difficulty for grid-based solvers of solute transport. When advection is the dominant transport mechanism, concentrations obtained from these solvers are prone to be influenced by oscillations and numerical diffusion, causing a negative impact upon the calculations related to chemical reactions. Particle methods are free of these issues thanks in part to advection being incorporated into the particle displacement. Therefore, simulations based on particles lead to an improved description of complex transport processes and related metrics, motivating their consideration for simulating reactive transport through aquifers. Nevertheless, limitations related to computational efficiency, or the availability of particle-based programs, still influence the ability of these methods to reach the end-users and real-world studies. The objective of this thesis is to contribute to the development of particle methods for reactive transport modeling in aquifers. The work provides novel methodologies, complemented by computer programs that can be integrated into the workflow of modelers. The first part of the thesis focuses on the progressive development of a solute transport code based on the Random Walk Particle Tracking (RWPT) method. Several components needed to be developed to achieve a functional program seamlessly integrated with groundwater flow models employed by hydrogeologists. The work began by implementing parallel capabilities into a well-known particle tracking code, which is the base for the main program. A complementary module provides the smoothed reconstruction of concentrations, compatible with non-uniform-weight particle sets and three-dimensional domains. These merge into a single major program implementing RWPT, which also required the formulation of a new method to displace solute particles exactly to the interface of a flow-model cell. The product of these developments is a new multispecies solute transport code, integrating several other functionalities necessary for reactive transport studies. The thesis continues with a chapter presenting a review of the Smoothed Particle Hydrodynamics (SPH) method, focusing on its ability to simulate anisotropic dispersion in heterogeneous porous media. The potential of SPH for this kind of problem is recognized in the literature. However, an unphysical effect seems to have