In a study of the quality of runoff from roof surfaces, five individual house roofs in the city of Bayreuth, Germany, were compared with experimental roofs on the university campus and with the depositing precipitation. While the city locations all bad different exposition characteristics. the campus site experienced urban background conditions without local emissions on or nearby the roofs. The concentrations of the substances under investigation showed a high degree of variability both within and in between single precipitation events. While the wet deposition load of organic micropollutants is increased by washoff of dryly deposited substances (e.g. PAH, ammonium) from the roof surfaces, the concentrations of inorganic ions like calcium were also increased by leaching from the roof material itself. Far both processes, there were marked differences between the roofs studied. PAH concentrations in runoff from one roof receiving emissions from old heating systems were elevated by more than one order of magnitude. According to the source variability for the respective substances, seasonal trends could also be detected. The investigation shows that it is difficult to generalise the pollution level of roof runoff even within a small area. This has to be taken into account for the planning of alternative urban drainage systems like infiltration facilities. (C) 1998 IAWQ Published by Elsevier Science Ltd. All rights reserved.
