A problem often occurring in practice is the validation of efficacy of a barrier wells designed to containment of pollution. Several methods and solutions have been tested , both mathematical and experimental (i.e. employing togheter mathematical models and tracers). Here is presented the case of a barrier consisting of two wells aligned across to the motion field of a groundwater, with the same discharge Q (Fig. 1); the line connecting the pair of wells is normal to hydraulic gradient.