Partitioning and First Flush of Metals in Urban Roadway Storm Water

Storm water runoff from urban roadways often contains significant quantities of metal elements and solids. These anthropogenic constituents are generated mainly from traffic-related activities. Metal elements partition into dissolved and particulate-bound fractions as a function of pH, pavement residence time, and solids concentration. Lateral pavement sheet flow from an experimental field site on a heavily traveled urban highway in Cincinnati was sampled during five rainfall runoff events in 1995. Results indicate that Zn, Cd, and Cu are mainly in dissolved form while Pb, Fe, and Al are mainly particulate-bound. Dissolved fractions of Zn, Cd, and Cu exhibited a strong first flush in lateral pavement sheet flow. Pb exhibited a weak first flush for all events. Event mean concentrations of Zn, Cd, and Cu exceed surface water quality discharge standards. Findings from this study will assist in the development of effective control strategies for the immobilization of metal elements and solids in urban runoff.