Switzerland has around 38,000 registered contaminated sites, including deposit sites, operational sites, shooting ranges, and accident sites. Natural hazards are an effective pathway for remobilising contaminants from such sites - either by physical processes, such as erosion through landslides and dynamic floods, or by chemical processes through static floods. In this study, we assess the exposure of contaminated sites to landslides and floods by spatially intersecting maps of contaminated sites and natural hazard zones. We present examples of contaminated site types where processes of landslides and floods can trigger remobilisation of contaminants. Our exposure analysis identified around 2200 sites prone to landslides and 11,500 sites prone to flooding. In Switzerland, the exposure of contaminated sites to floods, and the associated remobilisation of contaminants, is included in the assessment of the need for remediation. Our study shows that due to the significant number of contaminated sites at risk of landslides, this natural hazard should also be considered when assessing the need for remediation. Especially landslides that remobilise contaminated soil and reach surface waters are expected to cause widespread dispersal of contaminants. The presented method for assessing the exposure of contaminated sites to natural hazards is simple and cost-effective. As long as spatial data on contaminated sites and natural hazards are available, it can be applied in other contexts. Hence, the approach may also be of interest for other countries facing multi-hazard exposure of contaminated sites.
