Reactive transport processes in STEs have hardly been studied to date with the support of numerical reactive transport modelling. In groundwater science, reactive transport modelling has proven itself as an indispensable tool to untangle and quantify the coupled, nonlinear and typically non-intuitive interplay of hydrodynamic and biogeochemical processes. Applying reactive transport models in the postulated deep dynamic bioreactor below high energy beaches is a challenging yet promising way to unravel and elucidate the many intertwined processes. Subproject P6 will support the proposed research unit in its aim to understand these complex processes in the deep STE subject to highly transient boundary conditions. In close cooperation with and with steady feed-back from the project partners (P1-P5) we will develop reactive transport models capable of describing the processes and effects in the targeted laboratory experiments, as well as the composite behavior of the field-scale system. The resulting field-scale model will quantify the effects of the individual processes as well as the material fluxes in and out of the bioreactor. In cooperation with subproject P1 we will apply the final field-scale reactive transport model to a wide spectrum of field-scale conditions that are representative for high energy beaches in the world, thereby supporting the planning of Phase 2 of DynaDeep.