Geophysical Characterisation of a Former Waste Disposal Site in the Context of Landfill Mining

In the context of landfill mining, we conducted electrical resistivity tomography (ERT), borehole electromagnetics (EM39), and magnetometry campaigns to characterise the subsurface of a waste deposit. The electrical resistivity structures in the landfill appear tabular with a first layer (12-15 m) characterised by higher resistivities (> 10 ohm.m; with spots > 30 ohm.m) whereas the saturated zone (below 15 m) presents lower resistivities (< 4 ohm.m). Based on ERT images, we positioned 6 drillings, collected waste samples, and recorded in-situ measurements (distributed temperature and EM39) to confirm the ERT interpretation and bring out some limitations of the method. Magnetic field data were recorded in the same area. We noticed a clear distinction between the inside (high magnetic field gradient) and the outside (low variation) of the landfill. The large scale variation of the total magnetic field is compatible with the existence of a clinker dam below the landfill bottom membrane (known from historical information). Therefore, magnetometry could be used to detect variation in the waste composition (clinker, metallic drums, or municipal waste) but is also a cheap and powerful tool to map unknown landfill boundaries. Both aspects are crucial in the context of landfill mining.