This paper introduces an integrated approach for the assessment of receiving water quality and the relative contribution of the urban drainage system to perceived receiving water quality problems. The approach combines mass balances with relatively simple receiving water impact models. The research project has learned that the urban drainage system is only one of the determining factors with respect to receiving urban water quality problems. The morphology of the receiving waters and the non-sewer sources of pollution, such as waterbirds, dogs, or inflow of external surface water might be equally important. This conclusion underlines the necessity to changes today's emission based approach and adopt an integral and immission based approach. The integrated approach is illustrated on a case study in Arnhem, where the receiving water quality remained unsatisfactory even after retrofitting a combined sewer system into a separated sewer system.

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