Waste is, and always has been, generated around the world, around the clock. But in modern times it has been generated at unprecedented rates: municipal waste alone sums up to more than 2 billion tonnes annually. All this waste, in deposits, in landfills, creates several problems for society. For instance, the presence and extent of buried waste, especially older deposits, may be unknown and this creates difficulties during the establishment of new housing and infrastructure. In addition, landfill areas are often a source of contamination affecting the ground, rivers, lakes and groundwater far beyond their original physical limits. Despite this, waste deposits can also present an opportunity to society. With novel reprocessing techniques, landfills can be mined for recyclable metallic or plastic materials, whilst gas generated within the waste can be captured for power generation, if the structure and content of the landfill can be clarified.
The traditional way to investigate these problems and opportunities are by pointwise investigations, for example by drilling or digging. This is most often expensive, potentially hazardous and the data collected can be rather sparse. To create a more comprehensive picture of the subsurface conditions, different geophysical methods can be used as an efficient complement.
Old landfills often have high concentrations of heavy metals, nutrients and organic substances in the ground. Decomposition of carbonaceous material can produce methane, carbon dioxide and organic acids that contaminate the environment.
Guideline Geo´s resistivity techniques, utilizing either surface or borehole measurements, can solve most of the common questions regarding waste deposits and landfill areas. They will give a non-destructive and cost-efficient way of gaining a better understanding of the ground conditions, providing better data coverage than is normally achieved with traditional, discrete, point-by-point geotechnical investigations and sampling.
Different materials in the ground will have contrasting resistivities associated with them, and that resistivity can also vary within the material due to changes in composition, mineralogy, water content, and structural integrity. For landfill sites, the make-up of the content itself as well as the volume of water, leachate composition and temperature will affect the recorded resistivity. Areas with contamination will most likely decrease the resistivity, whereas areas with more stone/wood/building material will have a higher resistivity. The mix of materials in a typical waste dump can also create a sizeable IP (induced polarization) effect, indicating higher chargeability than the surrounding natural geology. This effect can delimit the extents of a waste pit more precisely than resistivity values alone, where the seepage of low resistivity leachate can ‘blur’ where the edge of the pit lies.
The ABEM Terrameter LS 2 is a perfect solution for examining waste deposits, but also useful for applications such as landfill and environmental surveys
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