Abstract
Urban sediment generated by stormwater management techniques are highly contaminated with various trace elements. The characterization of trace element speciation and mobility are critical information to improve environmental risk assessment. This study investigates the spatial and temporal variability of major and trace element release from a sedimentary layer in Django Reinhart stormwater infiltration basin (Chassieu, eastern suburbs of Lyon, France). Sampling was conducted for 3 zones and two dates. Chemical characterization was performed (X-Ray diffraction, ICP-AES). The samples were submitted to Acid Neutralization Capacity & Base Neutralization Capacity ANC-BNC tests, according to European standard 14429 (AFNOR, 2015). Solid matrices were mixed with acid or basic solutions and physicochemical parameters and major and trace element release (i.e. Al, Ca, Fe, P, S, Si, Cu, Zn and total carbon) were followed as a function of pH. The results show that the urban sediment has no significant spatial and temporal variability with regards to element release. This observation is all the more surprising that the samples were collected in three contrasting zones regarding stormwater supply and hydric conditions. Element release follows the same trends as a function of pH with a bell-shaped solubilization curve exhibiting with the highest solubility at extreme pH values. However, the samples showed slight differences concerning the release of major elements. Such differences are related to slight differences in total mineral contents (organic matter, carbonates…) and chemical composition of the sediments. The results show that despite the varying environmental conditions, the sediment chemical properties can be considered as very stable and uniform over space, depending mainly on the local geochemical context and watershed characteristics. This study highlights the strength and affluence of the information obtained by ANC-BNC tests on the release of major and traces metal elements by urban sediments and brings relevant information regarding the management of these sediments.
Highlights
Settlement and infiltration basins were developed to deal with the crucial issue of stormwater management
This study investigates the spatial and temporal variability of major and trace element release from a sedimentary layer in Django Reinhart stormwater infiltration basin (Chassieu, eastern suburbs of Lyon, France)
The results show that the urban sediment has no significant spatial and temporal variability with regards to element release
Summary
Settlement and infiltration basins were developed to deal with the crucial issue of stormwater management. Infiltration basins concentrate rainwater collected over watersheds of several hectares in small areas [1] This concentration of fluxes explains why suspended solids carried by stormwater accumulate at the soil surface and form a sedimentary layer with high trace metal and organic compound contents [2] [3]. There are many studies on the composition and characterization of sedimentary layers accumulated in stormwater infiltration basins These studies constitute a database on sediments contamination that points at the high contents of trace element (e.g. up to 2400 ppm of zinc, 500 ppm of lead, 300 ppm of chromium and copper) [2] [4]-[10]. To assess the risk of contamination of the subsoil and groundwater, the mobility of elements trapped in these sediments must be investigated [11] [12]
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