AUT050320081034 Environmental Relevance of Flooded MSW Landfills in Austria David Laner 1 , Johann Fellner 1 , Paul H. Brunner 1 , Clemens Neuhold 2 , Christian Kolesar 3 1 Institute for Water Quality, Resources and Waste Management, Vienna University of Technology, Austria 2 Institute of Water Management, Hydrology and Hydraulic Engineering, University of Natural Resources and Applied Life Sciences, Vienna, Austria 3 Austrian Federal Environmental Protection Agency, Vienna, Austria Contact David Laner Institute for Water Quality, Resources and Waste Management Karlsplatz 13/226, 1040 Vienna Tel.: +43-1-58801-22644 Facsimile.: +43-1-58801-22697 Email: d.laner@iwa.tuwien.ac.at Executive Summary Municipal solid waste (MSW) landfills pose a large, long-lasting risk potential for humans and the environment. The emissions occurring under average conditions in a landfill were subject to numerous research studies within the last decades and are therefore well docu- mented. In contrast, landfill behaviour and associated emissions in extreme cases such as flooding are widely unknown. However, a review of existing reports about environmental damages caused by landfills during floods indicates, that the released substances might be of environmental concern. It is the aim of this paper to determine the proportion of Austrian MSW landfills endangered by flooding, and to evaluate their potential environmental signifi- cance. The risk of flooding is evaluated for MSW landfill sites in Austria using data about flood risk zones (HORA). Based on the topology of the site and the flood risk zones, three categories of flood risk exposure are distinguished: “endangered”, “probably endangered”, and “probably not endangered”. Endangered and probably endangered sites are located in a potential inunda- tion area or close to a flood risk zone. For landfills assigned to one of these two categories, the potential emissions during a flood event are estimated by two substance release scenarios. The scenarios include intensified leaching processes of waste compounds, and loss of stability of the waste body due to erosion. The emissions based on these scenarios are used to evaluate the environmental relevance of flooded landfills. The results reveal that one third of Austrian MSW landfills is located in flood prone areas (within or next to areas flooded statistically once in 200 years), with only a small portion hav- ing flood protection facilities. According to the scenario analysis, and compared to average landfill conditions, emissions during a flood event might increase by up to six orders of mag- nitude, subsequently exceeding Austrian water quality standards for discharge into rivers. Based on these results, further research into landfill metabolism and associated geotechnical landfill properties seems justified and necessary.