Abstract
Electrical resistivity tomography (ERT) and ground magnetic surveys were applied to characterize an old uncontrolled landfill in a former exploited sand and gravel quarry in an area to the north-west of the city of Cologne, Germany. The total magnetic field and its vertical gradient were recorded using a proton precession magnetometer to cover an area of about 43,250 m2. The magnetic data were transferred to the frequency domain and then reduced to the north magnetic pole. The amplitude of the analytical signal was calculated to define the magnetic materials within and outside the landfill. Eight ERT profiles were constructed based on the results of the magnetic survey using different electrode arrays (Wenner, dipole–dipole, and Schlumberger). In order to increase both data coverage and sensitivity and to decrease uncertainty, a non-conventional mixed array was used. The subsurface resistivity distributions were imaged using the robust (L1-norm) inversion method. The resultant inverted subsurface true resistivity data were presented in the form of 2D cross sections and 3D fence diagram. These non-invasive geophysical tools helped us to portray the covering soil, the spatial limits of the landfill, and the depth of the waste body. We also successfully detected low resistivity zones at deeper depths than expected, which probably be associated with migration pathways of the leachate plumes. The findings of the present study provide valuable information for decision makers with regards to environmental monitoring and assessment.
Highlights
Geophysics has been successfully applied to investigate dumpsites and has become a very important tool in this regard
A combination of more than one geophysical method is commonly applied in near-surface studies to reduce the ambiguity problem related to the interpretation of the data
Local highly magnetic anomalies can be noticed within the undisturbed geology outside the landfill in the eastern part referring to metallic objects in the subsurface or possibly unexploded ordinances (UXO) from the Second World War
Summary
Geophysics has been successfully applied to investigate dumpsites and has become a very important tool in this regard. Several geophysical techniques improved their power in detection the geometry of waste deposits in a faster, cheaper, and non-destructive way. Despite the fact that current restricted national regulations prohibit non-controlled landfills, a tremendous number of old landfills have been found in Germany To remediate this problem, the determination of the vertical and horizontal distributions of buried waste is essential. The investigated area is an old landfill situated in the north-west of Cologne, Germany (Fig. 1). It was formed as the result of long-term dumping of various wastes. The investigated area was recently covered with grass Because this is an old site, it is difficult to know its exact distribution and the nature of the materials within it. The maximum depths are recorded at boreholes B3 (7.8 m) at the center and B11 (7.9 m) at the north-eastern corner of the landfill
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