Solute dynamics in the bed sediments of a stormwater infiltration basin T. Datry * , F. Malard, L. Vitry, F. Hervant, J. Gibert Ecologie des Hydrosyste `mes Fluviaux (UMR CNRS 5023), Universite ´ Claude Bernard Lyon 1, Ba ˆt. 403 (6 rue Dubois), 43 Bd 11 Novembre 1918, F-69622 Villeurbanne Cedex, France Received 25 January 2002; revised 11 November 2002; accepted 22 November 2002 Abstract Constructed stormwater infiltration basins have been used extensively in urban areas to dispose of stormwater and compensate for reduced groundwater recharge. Even though stormwater basins are designed to retain suspended solids, stormwater sediments accumulating in the infiltration beds may act as a source of dissolved contaminants. Contaminant concentrations in the bed sediments of a 30-year old basin have been determined and those constituents identified that were most likely to be eluted during present infiltration of stormwater. Bed sediments had high concentrations of organic carbon (100 g kg 21 sediment dry weight), nitrogen (6.2 g N kg 21 sed. DW), phosphorus (6.2 g P 2 O 5 kg 21 sed. DW), total hydrocarbons (2791 mg kg 21 sed. DW), and heavy metals (3341 mg kg 21 sed. DW). A total of 33 organic compounds were detected including 15 polycyclic aromatic hydrocarbons (52.9 mg kg 21 sed. DW,) and 10 polychlorinated biphenyls (547 mg kg 21 sed. DW). Chemical analysis of pore water stored in the infiltration bed and results of slow filtration column experiments showed that oxidation of organic carbon led to almost permanent anoxic conditions and resulted in the release of ammonium, phosphates and dissolved organic carbon during dry-weather periods. Hydrocarbons and heavy metals were rarely detected in pore water despite their high concentrations in the sediment. During rainfall events, the preferential flow of water through highly permeable areas of the infiltration bed with little sediment accumulation tended to separate stormwater sediment from infiltrating water, thereby reducing the leaching of nutrients. It is concluded that there can be a discrepancy between the contamination potential evaluated from the analysis of nutrient concentrations in inflow stormwater and the environmental risk resulting from the percolation of inflow water through a layer of permeable sediment. q 2003 Elsevier Science B.V. All rights reserved. Keywords: Urban water; Stormwater sediment; Stormwater infiltration; Heavy metals; Hydrocarbons; Nutrients 1. Introduction Urbanization has been a dominant demographic trend in the second part of the 20th century. Cities now contain about a half of the world’s population, and this proportion is expected to reach 61% within the next 30 years (Grimm et al., 2000). The increase in urbanization poses several environmental concerns such as air pollution, degradation of surface water and groundwater resources, and changes in land cover far beyond the city’s boundaries. Whereas the influence of domestic sewage effluents on streams and ground water has long been studied (Aulenbach, 1974; Robertson et al., 1991; Arnade, 1999), the potential 0022-1694/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved. DOI: 10.1016/S0022-1694(02)00388-8 Journal of Hydrology 273 (2003) 217–233 www.elsevier.com/locate/jhydrol * Corresponding author. Tel.: þ33-4-72-43-29-45; fax: þ 33-4- 72-43-15-23. E-mail address: datry@univ-lyon1.fr (T. Datry).