Geological background – The influence on waste management concepts Reinhofer M., Proske H., Pirkl H., Kellerer-Pirklbauer A., Trinkaus P. Abstract Geological background levels for most of the geological units in the federal state of Styria were defined by the analysis of numerous geo-chemical databases with the aid of a geographical information system (GIS). The evaluation was done with geostatistical methods including the elements cadmium, chromium, copper, mercury, nickel, lead and zinc. One application of this information system was the statistical analysis of heavy metal contents of biological waste compost and communal sewage sludge. The input data originated from all commercial and agricultural composting plants and communal waste-water treatment plants located in Styria covering a 10 years period. The main question within this investigation was to figure out if there is a statistically provable context between the heavy metal contamination of organic waste materials and the geological background level of the area of origin. This allows to judge which contaminations are avoidable and which ones are generated by the natural environment. The statistical analyses of the compost and sewage sludge data showed a very high probability of a direct correlation between high heavy metal contents and the geological background levels for some elements. Introduction The heavy metal content is one of the decisive quality criteria for the application and reuse of organic waste or products out of organic waste - e.g. for biological waste compost or sewage sludge. In general the amount of heavy metal contamination is determined by the nature and kind of the waste materials, by the treatment of raw materials and by the composting technique itself. In addition to anthropogenic or technogenic transfer paths the natural background levels in the bedrock or soil material and of mineralised water at a given location can affect the heavy metal content of biological waste as compost or sewage sludge. As geological background levels show high regional variations, this factor should be considered for any evaluation and for any comparable assessment of e.g. compost qualities (class A+, A and B). Methods and results Within this project the actual geological background level was entered into a GIS covering most of the federal state of Styria (fig. 1). The determination of the geological background level was based on numerous geo-chemical databases such as stream sediment investigations (geochemical atlas, Thalmann et al. 1989), soil sampling programs (Neinavaie 1989, Pirkl 1994, Pirkl et al. 1994, Landwirtschaftliches Versuchszentrum 1999, 2000) and investigations aimed at the exploration of raw materials (Haditsch et al. 1981, Weber 1990). The evaluation was done by means of univariate and multivariate geostatistical methods including the elements cadmium,