The Barriers Approach has been developed to identify possible ways to trace or decrease the sources of chemicals, to estimate the flows of chemicals in a stormwater system. Four kinds of barriers have been identified: organisational, structural, process, and behavioural. In order to investigate and explain the barriers, a case study was carried out in Hammarby Sjöstad. In this study, three scenarios were examined: a combined system, a separate system with no treatment, and a separate system with treatment by different BMPs. For the combined system, most of the pollutants are bound for the sewage sludge. For the separate system with no treatment, the pollutants will end up in the receiving waters, while for the separate system with treatment, most of the pollutants are bound for the sediments or soil