Groundwater contamination by heavy metals from infiltration facilities receiving road runoff is of potential concern. In this study, sorption tests were conducted to evaluate the influence of the water quality of road runoff, especially dissolved organic matter (DOM), on the sorption of heavy metal species by soakaway sediment. Sequential batch tests were conducted to assess metal sorption by the soakaway sediment receiving road runoff from residential and heavily trafficked areas. Ni was adsorbed by the sediment, indicating that soakaway sediments function to prevent groundwater contamination by Ni. In contrast, Zn was released from the soakaway sediment in sorption tests using heavily trafficked road dust leachates. Ni, Cu, Zn, and dissolved organic carbon concentrations were higher in soakaway sediment leachates obtained by sorption tests using heavily trafficked road dust leachates than those using residential road dust leachates, suggesting traffic activities contaminate these pollutants. A large portion of Zn, released from the soakaway sediment, existed as stable complexes. DOM in road runoff possibly enhances the release of Zn from the sediments within inflitration facilities and might cause groundwater contamination. (c) 2008 Elsevier B.V. All rights reserved.