Assessment of metal and PAH profiles in SUDS soil based on an improved experimental procedure

The increasing use of infiltration-based systems for stormwater management questions the soil's ability to act as a long-term filter for runoff contaminants, and brings about operational matters regarding the most effective maintenance practices to enhance contaminant retention in SUDS. This paper reports the vertical extent of metal and PAH contamination in the soil of seven source-control devices in operation for more than 10 years, assessed via a two-step sampling strategy to optimize the representativeness of the contamination profiles. Metal distribution was typically characterized by a significant surface buildup, followed by a decrease in concentrations with increasing depth, usually coming close to the background values. PAH were more heterogeneously distributed with depth, but their accumulation was globally restricted to the upper 10–40 cm. This indicates an interesting potential for pollution interception by the upper horizons of soil, but does not necessarily prevent from downward fluxes, even while measuring low surface contents, as deeper strata may have lesser retention capacities. Specific amendments of the surface soil may help prevent this problem. Surface soil renewal – which would be necessary over 2.5–30 cm in four sites, according to the “strictest” standards for soil remediation – may regenerate the soil's sorption potential, but such a practice could disrupt the interactions with the local ecosystem, so this should be carried out exceptionally and not as a preventive measure. •A two-step sampling procedure is relevant for assessing soil contamination in SUDS.•The vertical extent of soil contamination is mainly limited to the upper 10–40 cm.•High contents of sparsely documented metals (Cr, Ni, Co, Mo) were sometimes measured.•The retention capacities of lower horizons may be lesser than that of surface soil.•Soil amendments at the surface may help prevent downward fluxes of solute contaminants.