Accumulation de métaux et HAP dans le sol de différents ouvrages d'infiltration

Sustainable Drainage Systems are increasingly used for stormwater management. However, the generalization of runoff infiltration in urban watersheds raises some concerns regarding the soil's ability to retain ubiquitous runoff pollutants. This question was addressed via field campaigns and modelling approaches. A two-phase sampling methodology was carried out on 11 infiltration-based facilities with contrasting characteristics, leading to cartographies of metal contamination in the surface soil, and vertical profiles of metal and PAH contents, along with different explanatory variables. The spatial distribution of trace metals in the upper horizon displayed a systematic structure with respect to the inflow area, and revealed the time-integrated signature of non-uniform infiltration fluxes and flow pathways at the surface. In the most contaminated zone of the facilities, a significant enrichment of metals and PAHs was detectable until 10 to 40 cm depth. Soil acts as an effective "filter" towards these persistent urban contaminants, due to the combination of mechanical and physicochemical processes (filtration and sorption); in return, surface contents from 7 study sites exceeded "intervention thresholds" for multi-functional areas - as defined in various international soil clean-up standards. In these devices, the area which would require soil remediation after ≥10 years of operation was found to be laterally and vertically limited. The modelling approach demonstrated that a device's lifespan can be substantially improved via an organic amendment of the surface horizon, which increases the retention of dissolved contaminants, or by ensuring diffuse water inflow at the soil surface. Reducing runoff volumes at the facility inlet - e.g. via the disconnection of "nonemissive" surfaces in the catchment area - also contributes to decreasing the rate of contaminant migration in the soil.