In German cities and counties most of the rainwater roof run-off, together with wastewater from households and small industries, is transferred to sewage treatment plants (STPs). Thus, a much larger volume of water has to be processed at STPs during rainfall. In order to maintain proper working conditions the excess wastewater has to be stored in modified sewer systems or in stormwater overflow tanks. Instead of storing large volumes of water, it is more economic to infiltrate the rainwater run-off into the soil. This alternative can also be favorable from an ecological point of view because the run-off water can be used for the replenishment of groundwater resources.

Due to increasing road traffic and other sources of immission, however, rainwater nowadays is often contaminated with pollutants. Seepage of rainwater could therefore lead to a contamination of soil and groundwater. One question related to this problem is whether roof areas act as a sink or as a source for pollutants. This will likely depend on the type of roof material as well as on other factors and is being investigated in the project “Quantitative assessment of pollutants on urban areas with a combination of chemical and image processing methods”. This project is being funded by the Ministerium für Wissenschaft, Forschung und Kunst Baden-Württemberg and started in August 2003.

The incomplete combustion of fossil fuels results in the formation of pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs). Some PAHs are known to be carcinogenic compounds. PAHs can be transferred from the gas phase (atmosphere) to the liquid phase (rainwater) either through dissolution of gaseous PAHs or through suspension of PAH-loaded particles in rainwater. One aim of this project therefore is to determine PAH concentrations in run-off waters from different roof materials (e.g. clay, concrete, bitumen, zinc, copper) as a function of season and rain intensity. Furthermore, the input of metals into rainwater run-offs will be monitored simultaneously.

Findings of the experiments with model roofs will be compared to results from real roof areas. Using laserscanning and hyperspectral methods, roof areas and materials will be determined for a selected larger urban area. This work will be carried out by the working group of Prof. Hans-Peter Bähr, Institut für Photogrammetrie und Fernerkundung (IPF)/ Universität Karlsruhe (TH) who is our associated partner in this project. Based on remote sensing and chemical analysis data, an extrapolation will be conducted to quantify the input of PAHs and metals from larger urban areas into rainwater. Contact at the IPF: Dipl.-Ing. D. Lemp (lemp ∂does-not-exist.ipf uni-karlsruhe de) and Dr.-Ing. U. Weidner (weidner ∂does-not-exist.ipf uni-karlsruhe de).