Groundwater resources in a Mediterranean mountainous region: environmental impact of road de-icing

Water from mountainous regions is a strategic natural resource. In Mediterranean mountainous regions, which, in many cases, correspond to protected areas, high-altitude roads are often the main threat to the sustainability of water resources. In these regions, the regular socioeconomic functioning requires frequent road de-icing operations which normally consist of spreading NaCl and other chemicals, such as CaCl₂, in pavements. The main purpose of this research is to assess the environmental impact of road de-icing on groundwater resources in a Mediterranean mountainous region and to describe it by means of a hydrogeological conceptual model. The research focused in a cross-sectional sector located in Serra da Estrela (Central Portugal), where a hydrogeological inventory was carried out, followed by hydrogeochemical and hydrogeophysical studies. The results clearly identify different hydrogeochemical signatures in polluted (Cl–Na facies and higher EC) and unpolluted (HCO₃–Na, Cl–Na, and very low EC). The relation of hydrogeochemistry and altitude is complex and depends on both natural processes (namely, water–rock interaction) and anthropic processes (de-icing operations). The hydrogeophysical survey systematically identified the presence of a pollution plume migrating downstream from roads.