Storm water pollution in the urban environment

Nonpoint pollution resulting from urban surface runoff has been identified as one of the major causes of the deterioration of the quality of receiving water bodies. In order to characterize the first flush phenomenon connected to different types of urban surfaces two monitoring systems have been installed in the experimental catchment of Villa Cambiaso, University of Genoa (Italy), for sampling separately roof and road runoff. Results of the first flush flow monitoring campaign held since January 2002 in the town of Genoa are presented for the following parameters: total suspended solids, COD, NH4+, pH and heavy metals in dissolved form (Zn, Pb, Cu, Cd, Cr, Ni). Cumulative load curves are provided for all monitored water quality parameters. As for the road runoff, the magnitude of the first flush in the monitored events is observed to vary with the duration of the antecedent dry weather period while the influence of the initial rainfall intensity was observed on the occurrence of the phenomenon. Regarding roof runoff, the entity of first flush of heavy metals in dissolved form is affected by both rainfall event characteristics (intensity and total depth) and environmental conditions prior to the rain event; the occurrence of first flush of suspended solids is is observed to vary with the duration of the antecedent dry weather period which regulates pollutant building up.