Size Distributions and Settling Velocities of Suspended Particles from Road and Highway

Characterization of particles from road runoff is very important for the selection of Best Management Practice (BMP) in the stormwater management. In this study, runoff samples during two rainfall events at four sites in Gyunggio-Do were collected and Particle Size Distributions (PSD) in the size range of 2-880 mu m were determined. Then number and mass fraction of each size range was obtained from a total of 89 samples. Also, rainfall amount, flow rate, and other pollutants in samples were analyzed. Particles with less than 5 mu m accounted for more than 80% of number fraction while their mass fraction was about 12%. Particles larger than 50 mu m contributed more than 40% of mass fraction. Partial Event Mean Concentration (PEMC) of particle showed inverse relationship with accumulated rainfall and sharply decreased at the early stage of rainfall, implying that the first flush is major contribution to particle runoff. Other pollution parameters such as turbidity, TSS, BOD, TN, and TP also have similar temporal runoff trend with the PEMC. Particle settling velocities of runoff particles were obtained by column tests and their values were compared with theoretical velocities. Based on the settling velocity distribution, removal efficiency of particles from runoff by sedimentation was evaluated.