Patterns of roof runoff contamination and their potential implications on practice and regulation of treatment and local infiltration

Roof runoff water was sampled from an experimental roof system and from house roofs in the city of Bayreuth, Germany. Samples were analysed for organic micropollutants, heavy metals and sum parameters. The pollution level and the shape of the runoff profiles are dependent on the individual properties of the precipitation event and the roof, but patterns with high concentrations at the beginning of the event and a subsequent decrease (first flush effect) are very typical. For dissolved substances, the profile can often be well described by a negative exponential function. Metal surfaces on the roofs cause extreme runoff pollution with heavy metals (Cu, Zn) that constitutes an environmental hazard. It is concluded that there is a need for the development of flexible drainage strategies for surface runoff and that metal surfaces should be avoided on roofs.