Partitioning of zinc, copper and lead in urban drainage from paved source area catchments

Abstract Representation of metal partitioning in urban drainage is required when determining loadings, treatment, maintenance and regulatory compliance. This study examined partitioning and transport of metals from urban paved surfaces: highway, parking lot (landside) and apron terminal (airside) within aviation site, terminals within port area. Equilibrium concentrations of metals and particulate matter (PM) using a non-parametric analysis for a series of six paved surface area catchments were compared. In particular, two American highway sites, and four Italian sites located in the Liguria Region (two port terminal and two aviation sites) are examined and compared with event-based concentrations collected from catchments with similar land uses. The highway sites are more heavily loaded with PM (up to averagely 470 mg/l of PM as total suspended solids) while the terminal port ones reveal the most significant mass delivery of metals, as high as 1 mg/l. Transport of metal phases on an event basis, thus relating hydrology and PM mass delivery impacting metal partitioning, are examined. At all catchment sites, copper and lead reveal the greatest affinity for the particulate-bound fraction while zinc shows significantly different partitioning behaviour that may be partially depending on the specific site characteristics and the chemistry of zinc. Partitioning, indexed through a partitioning coefficient, Kd accounts for hydrologic transport, PM transport and interactions with and between metals. Kd can vary by orders of magnitude across a runoff event for the source area catchments of this study. A Kd condition in the range of 104 to 105 l/kg appears to be approached for all metals as elapsed runoff time increases. Based on the variability of partitioning, whether intra- or inter-event, results indicate that paved source area treatment requires a combination of sedimentation, filtration and adsorption mechanisms for in-situ unit operations and processes.