Aquifer thermal energy storage (ATES) is a sustainable technology that provides thermal energy to buildings in temperate climates. The principle of ATES is to temporary store thermal energy in aquifers in a warm and cold well in order to use this thermal energy for heating and cooling in the next season. Because the available subsurface space is limited, congestion problems can occur in areas with high ATES density. In these areas a conflict of interests exists between private parties who want to achieve maximum efficiency by avoiding negative influence of other systems (leading to large buffers between wells), and the public interest to maximize the amount of thermal energy stored in the aquifer. One solution to this problem is to reduce the distance between wells of the same temperature, creating one large thermal zone around the wells. The main goal of this research is to quantify the change in performance of ATES systems when their thermal zones are connected. The results of this research are as follows. Connecting the thermal zones of wells of the same temperature increases the thermal recovery efficiency of individual systems. This increase is between 8-15% for an average ATES system with a storage volume of 250.000 m³. It is even higher for smaller systems, 15-40% for a system with a storage volume of 50.000 m³. This is crease in efficiency is due to lower losses to the surroundings due to a lower area of the thermal zone compared to the volume of the thermal zone. The reduced distance between wells leads to an increase in pumping energy. Therefore an optimal distance between wells of the same temperature of 0.5 times the thermal radius is found. The distance between wells of opposite temperature should be larger than 3 times the thermal radius.