The soil and groundwater of the Rotterdam harbor area have become polluted as a result of long-term and large-scale industrial activities. This pollution is extensive and complex, and it is also a cross-boundary problem locally. Dealing with pollution on a case-by-case basis is not very cost-effective. Deltares has therefore opted for a joint mega-site approach, as management strategies can then be orchestrated and measures prioritized. By taking into account the natural resilience of the soil and groundwater system, it is possible to determine which pollutants are critical and should be dealt with. The mega-site approach also makes it possible to combine spatial planning, such as the redevelopment of industrial locations, water management and subsoil use, while eliminating the risks of large-scale ground and groundwater pollution.