In Switzerland, there are more than 4'000 contaminated sites needing remediation in the next decades. Some of the remediation projects are especially large – over 100 Millions € - and highly complex. On behalf of the Swiss Federal Office for the Environment (FOEN), the authors developed a guideline (in press) to support the authorities which are challenged by such complex projects.
After having identified the success factors and key challenges of three sites being currently remediated, a project typology, based on four dimensions (technical, legal, socio-relational and management), has been developed. Further, a complexity grid, inspired by the project complexity model of Kathleen Hass, has been developed, allowing a qualitative identification of the main sources of complexity. Finally, success factors, recommendations and tools for key elements like goal-setting, decision-making and steering, stakeholder-management, project-organisation, participation and communication, planning, uncertainty and risk-management, culture and leadership, are suggested.

Via Philippe Vallat