Airborne geophysics in mapping contaminant plumes from landfills

Geological Survey of Finland (GTK) has carried out low altitude airborne geophysical surveys in Finland since 1972. Today 80% of the country has been measured. The following systems are in use: magnetic, gamma radiation and vertical coplanar EM and VLF electromagnetic. Airborne geophysics is a fast method to map landfill areas at regional scale. A successful example in Finland is the airborne detection of leakage from Rovaniemi landfill, in Northern Finland. A clear quadrature electromagnetic anomaly (AEM) associated with the landfill was found. The resistivity of the anomaly source is less than 20 Ohm m, whereas the surrounding resistivity is 100-300 Ohm m. In order to explain the AEM-anomaly sources ground geophysical studies were conducted. Combining geophysical results with geochemical analyses from peat and ground water, the contaminant plume has been confirmed. GTK done airborne measurements at Ammassuo, the large municipal landfill of Helsinki region. The landfill area has been mapped in national airborne mapping program (1984) before the operation started (1987). The second survey was done using tighter flight line spacing. Magnetic anomalies indicated the metallic waste and human constructions. The attenuation of the gamma radiation revealed wet areas of the landfill. Comparing the old and new AEM results it was possible to detect accurately and reliably weak conductivity anomaly variations around the landfill area but there are no evidence of significant leakages.