Stormwater basins as potential sources for road runoff infiltration into the aquifer – case study of eight basins in Wolfisheim, Alsace
Four stormwater basins located alongside a country road (Bas-Rhin, France) and designed to mitigate runoff road water pollution have been studied. Each system consists of a storage basin, designed to prevent infiltration and equipped with a “planted area”, followed by a planted infiltration basin. Collection of infiltrating water (25 cm and 50 cm depth) is achieved with draining lysimeters. Piezometers were set up to perform groundwater qualitative and quantitative analyses (Polycyclic aromatic hydrocarbons (PAH) and metal concentrations only). Climate parameters were measured in situ by a weather station, which allowed computation of runoff, infiltration, evaporation, evapotranspiration and evapoconcentration fluxes. No clogging could be observed after rain events, as shown by excellent infiltration capacity measurements. Plants developed well and the surface particulate phase was visually observed to be well sieved by this system. Monthly sampling revealed the presence of PAHs and metals (aluminium, barium and lead) in surface and infiltrated water, yet only aluminium and barium (30-130 μg∙L‐1) could be detected in groundwater right below the stormwater basins. Ecotoxicity tests performed on infiltrating water showed no adverse effects on two groundwater ecosystem trophic levels as well as surface water organisms. Methodological and technical guidelines are provided to enhance technical and scientific knowledge on road water infiltration systems. Structure, role, functioning of these systems as well as interactions among soil, plant and water within them could thus be better understood.