Storm water pollution in the urban environment of Genoa, Italy

Nonpoint pollution resulting from urban surface runoff is recognized as one of the major causes of quality deterioration in the receiving water bodies. In order to investigate 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), to sample separately roof and road runoff. In the monitoring campaign, which has been held since January 2002 in the town of Genoa, the following parameters have been investigated: total suspended solids, COD, NH4+, pH and heavy metals in dissolved form (Zn, Pb, Cu, Cd, Cr, Ni). As for road runoff, TSS and COD concentration values exceed water quality standards, while the concentration of zinc is relevant in roof runoff. A strong correlation is observed between COD and TSS concentrations. The Event Mean Concentration (EMC) of various pollutants in road runoff is comparable to the typical values observed in residential areas, according to the American and European studies reported in the literature. Two dimensionless representations of the wash-off process are provided for TSS and zinc based on the cumulative pollutant mass and the Partial Event Mean Concentration (PEMC). First flush of suspended solids is observed in more than 70% of the monitored rainfall events. Regarding roof runoff, the magnitude of first flush for heavy metals in dissolved form is affected by both rainfall characteristics (intensity and total depth) and the antecedent environmental conditions. Simple correlations between rainfall characteristics (average and maximum rainfall intensity, total rainfall depth, total runoff volume, maximum runoff discharge, antecedent dry weather period) and the EMC of TSS have been investigated: good correlation is only observed with the maximum rainfall intensity.