Our PhDs Leonardo and Chiara showed a physical model to high-school students during the POLIMI open day held on 1st April in Campus Leonardo, Milano. The model represents a vertical section of a typical subsurface system comprising different geomaterials. Chiara and Leonardo explained to future engineers what is the effect of pumping on natural flow and showed, through the injection of tracers, what are the main mechanisms driving contaminant transport in groundwater bodies.