Runoff pollutants of a highly trafficked urban road--correlation analysis and seasonal influences

The quality of road runoff at a highly trafficked road has been studied for 2 years. 63 storm events have been sampled and analyzed. Besides pH value and electric conductivity the concentrations of zinc (Zn), copper (Cu), lead (Pb), nickel (Ni) and cadmium (Cd), both in dissolved and particulate form, de-icing salt, total and dissolved organic carbon (TOC and DOC), suspended solids (SS) have been monitored. Correlation analysis showed a significant relationship between the total metal concentrations with TOC and SS. A considerable seasonal increase in pollutant concentrations has been observed for Cu, TOC, SS, pH value and especially for Zn during the cold season. The mean values during winter time were multiple times higher than measured during the warm season. In contrast, the fractionation of heavy metals was not affected by seasonal variations, but remarkable fluctuations were observed between different rain events with dissolved fractions above 90%. As a result of this and due to the high pollutant load on fine particles, best management practices (BMPs) only implementing sedimentation are not recommended for treatment of heavily polluted urban road runoff. From the data obtained it can be concluded, that the de-icing salt has only a weak influence for higher pollutant concentrations. The increase of heavy metal concentrations occurs because of increased tear and wear due to application of gravel at cold weather conditions. No significant influence of the length of antecedent dry weather periods could be observed most likely due to street sweeping, winds and air turbulences caused by traffic.