Seasonal aquifer thermal energy storage and recovery (ATES) help urbanized areas to contribute to their energy demands. We assess the potential of ATES in the Brussels-Capital Region, Belgium with groundwater flow, heat and reactive transport models. Situated in the phreatic Brussels Sand aquifer, they indicate that ATES systems are unfeasible for hydraulic conductivities of 4.2e-6 ms-1. At low groundwater flow velocities however, ATES are feasible for hydraulic conductivities of 1.4e-4 ms-1. Iron(hydr)oxide precipitation during ATES operation is investigated with reactive transport models. To avoid well clogging groundwater should be pumped only from above or below the aquifers redox boundary.