Building products as sources of environmentally relevant substances in rainwater runoff   

At the end of last year, the results of the BaSaR project were presented in a public web seminar. One of the main questions of the project was: Can building façades and roofs affect water quality? The fact that trace substances are relevant in urban stormwater runoff and that their composition is strongly influenced by the type of catchment area has already been impressively demonstrated in KWB’s OgRe project. The extent to which environmentally relevant substances can be washed out by rain from new urban development and redevelopment areas has been investigated in practice over the past three years in the BaSaR project, funded by the Federal Environment Agency, together with the University of Applied Sciences of Eastern Switzerland and the Berliner Wasserbetriebe.

For this purpose, for one and a half years during rain events emissions were recorded for two new building sites in Berlin focusing on the buildings (façade and roof) and the area runoff. In addition, the release behaviour for the building products used was determined in the laboratory and the substance discharges were modelled with the COMLEAM software. This combined approach made it possible to determine the potential of the loads under controlled conditions and to compare them with the substance inputs into the rainwater determined under real conditions. It was shown that biocidal agents from façades such as diuron and terbutryn, root protection agents from roof surfaces and also the heavy metal zinc are discharged in quantities that can lead to target values (EQS) being exceeded, depending on the type of water body. In addition, it has been found that a large part of the façade emissions can seep away diffusely on site and thus, in the case of insufficient retention in the soil, an impairment of the groundwater is possible.

Based on the results of the study, concrete measures for the avoidance and reduction of substance emissions from building products into the urban environment were derived and compiled in a guideline and action fact sheets for planners, architects and authorities. All of these are now available on the website of the UBA (in German). With the variety of measures, sustainable construction is possible without affecting water bodies and groundwater.