With the incentive to reach the energy saving and CO2 emission reduction targets of the Netherlands, the application of Aquifer Thermal Energy Storage (ATES) is expected to increase sharply during this decade [2]. With limited aboveground and underground space, well arrangement is becoming difficult in busy areas with a rapidly growing number of ATES systems. Master plans were proposed to achieve optimal use of the subsurface, especially in such busy areas. This study aims at improving the robustness of such master plans. A two-stage method is proposed to obtain such robust master plans. It was applied to one of the seven available and investigated master plans, i.e. the Parooldriehoek in Amsterdam. The studied master plan was optimized in the first stage by replacing its design parameters with their best alternatives. In the second stage this so-optimized plan was tested to assess its flexibility to handle climate change and additional future users. As a result, the studied master plan could successfully be lifted to a higher level of robustness compared to the original.