Hyporheic zones (HZs) are key compartments for the functioning of aquatic ecosystems. As dynamic and complex transition regions between rivers and aquifers, they are characterized by the simultaneous occurrence of multiple physical, biological and chemical processes. Turnover and degradation of nutrients and pollutants figure among the prominent ecological services the HZ provides. We are facing a significant knowledge gap in the understanding of how hyporheic processes are linked and how they impact on each other. The concept of HypoTRAIN has been tailored to fill this gap. Collaborative research with state-of-the art technologies from multiple disciplines (hydrology, ecology, microbiology, engineering, environmental physics, contaminant science, modelling) will generate new mechanistic insights into the functioning of HZs. A group of ESRs (PhD students) will be educated using the multi-faceted nature of HZs as the central theme of the training program. Research focus of the two PhD projects at ACES is in-situ analysis of hyporheic transformation of organic micropollutants and using benchmarking as a tool to improve the assessment of chemical persistence.