Characterization of solid and metal element distributions in urban highway stormwater

Urban drainage from paved surfaces transports a wide gradation of solids ranging from sub-micron particles to gravel size aggregates. This study measured physical characteristics of solids transported in lateral pavement sheet flow from a heavily traveled urban roadway in Cincinnati. The physical characteristic measured was particle size which was used as a surrogate of specific surface area. Solids were sorted according to particle size distributions (PSD). Solids ranged from smaller than 1 μm to greater than 10,000 μm. Particles larger than 25 μm were separated mechanically to generate PSDs. Flow rate and duration controlled the yield and size of transported solids. Metal element analysis of PSD from snow and rainfall events indicate that Zn, Cu and Pb mass increase with decreasing particle size. Cd did not exhibit a similar trend. Results provide guidance for assessment of urban runoff water quality impacts and design of in-situ treatment strategies.