f Detection of old waste depostits and their contamination by using geophysical methods: Two case studies

Waste deposits constitute a massive risk for the environment. Their re-development needs most exact information about their extent, content and their geological situation. This information can be improved cost-effectively and fast utilizing non-destructive geophysical methods, such as magnetic, electromagnetic and geoelectrical field measurements. To demonstrate the effectiveness and advantages resulting from combining these methods, two case studies are presented. 1) Waste deposit in Molln, Upper Austria: The waste of an aluminium-factory was deposed in a river. No precautions were made. The records showed no details about the quantity of the waste and the extent of the polluted area. Using geoelectrical-Wenner-array-measurements these informations could be retrieved. A 3m-array-distance was choosen for this purpose. The boundary of the waste deposit and even areas of high contaminations could be determined with high precision. The waste deposit showed lower apparant resistivity values than its surroundings, which consists of sand and gravel - both showing very high apparent resistivity values (> 500 Ohm-m). In addition, using two deep soundings after Schlumberger the specific resistivity of the waste deposit and of its surroundings could be determined. 2) Waste deposit in Karling, Upper Austria: The waste deposit, probably containing common house-garbage, was surveyed using magnetic, electromagnetic and geoelectrical methods. Based on five geoelectrical deep soundings after Schlumberger the hydrological and geological situation in the aerea of the waste deposit was determined. A 12 m thick ground-water-layer was endangered by this feature. At a depth of 18 m a layer showed up, which can play an important factor during a future re-development of the waste site. Electromagnetic and magnetic (total intensity and gradiometer) surveys were carried out with a measurement distance of 5x10m. The electromagnetic survey showed clearly the surrounding of the waste deposit and a strong contamination. The magnetic survey showed areas of strong anomalies, which are not typical for a normal household-waste. Hence, in the investigated area one should also expect to find steel barrels, car-wracks etc.