13 th International Conference on Urban Drainage, Sarawak, Malaysia, 7-12 September 2014 1 Substance flow analysis of the primary non-point sources of pollution of urban runoff. A comparative assessment of three catchments. Guido PETRUCCI 1,2 , Marie-Christine GROMAIRE 2 , Ghassan CHEBBO 2 1 Vrije Universiteit Brussel (VUB), Earth System Sciences (ESSc), Brussels, Belgium 2 Université Paris-Est, Leesu, Champs-sur-Marne, France *Corresponding author’s e-mail: guido.petrucci@vub.ac.be ABSTRACT Quantification of the different urban non-point sources of runoff pollution is a primary task in order to reduce pollutant loads from urban areas and to protect water bodies. To understand the link between urban land-use and pollutant source distribution, a substance flow analysis is realized for three catchments and four pollutants: Cu, Pb, Zn and PAH. Results are coherent with available measurements and among the catchments. The analysis identifies the ratio between traffic volume and impervious area as a potential indicator for source distribution of Cu and PAH. Results for Pb and Zn show the relevance of building materials used in small roof elements. KEYWORDS Substance flow analysis; runoff pollution; urban catchments; metals; land-use. INTRODUCTION Non-point pollution of urban runoff is considered an important cause of degradation of aquatic environments and ecosystems since several decades. The interest for this type of water pollution is still increasing because of the evolutions in the regulatory framework for micropollutants. Analyses of the sources and fluxes of pollutants have flourished in recent years, often gathered under the name of “substance flow analyses” (SFA; Hansen and Lassen, 2002; Brunner and Rechberger, 2003). While direct measurements at the outlet can help to assess the total flow of pollutants from the catchment to the environment, SFA can provide, in addition, an insight on the relative weight of each source on the global urban flow of pollutants (Davis et al., 2001; Bjorklund, 2010; Chèvre et al., 2011). The extended knowledge provided by SFA has been mainly used, for non-point pollution, to analyze specific catchments and issues in order to orient policy-making and research. In most existing studies, in fact, SFA are realized on a single catchment in order to identify the most relevant sources of pollution and the potential mitigation measures. Another potential use of SFA is to compare different sites, linking the catchment characteristics to specific non-point source “signatures”. The purpose is to investigate if and how land-use and activities inside a catchment determine its pollutant outflow. This kind of application can contribute to explain part of the high variability of pollutant emissions to stormwater, a topical question for urban runoff pollution research (Smullen et al., 1999; Gasperi et al., 2013). This communication illustrates the results of an SFA applied to water runoff from three urban catchments and for four pollutants: Cu, Pb, Zn and PAH. Differences among the catchments