First flush analysis of heavy metals in expressway stormwater runoff

The focus of this study was the heavy metals,Cu,Zn,Pb and Cd,commonly found in land used for transportation. Dissolved and particulate-bound fraction concentrations of these metals were measured during 8 rainfall-runoff events on a representative expressway pavement in Nanjing. On the basis of a qualitative evaluation of flushing,the first flush of heavy metals was quantitatively analyzed,and the influences of hydrologic characteristics on the first flush are discussed. The results of the analysis of dimensionless normalized cumulative mass and volume curves indicated that total,dissolved and particulate-bound metals,except dissolved Pb,exhibited a pronounced first flush in most events. The second flush also exhibited in some events. The initial flush ratio demonstrated that about 35% to 39% of heavy metals could be removed from road runoff by intercepting and treating the initial 25% of the runoff water. The sequence of strength of the first flush of total metals was:CdCuZnPb; for the dissolved metals:CdZnCuPb; and for the particulate-bound metals:CuCdPbZn. Correlation analysis suggested that the influence of mean rainfall intensity on the first flush of metals was significant,but there was no significant influence caused by other rainfall factors.