In connection with the densification of cities, which often means utilising land formerly used by industry, this method can be used to see where there is contamination below ground.
The measurements can also be used to meter the extraction of old deposits. Such deposits can contain thousands of tons of metal, plastics and large quantities of methane gas, generated by household waste. A deposit can therefore be seen as a type of recoverable mine, which has led to the term “landfill mining”.
A survey could involve a measurement area of 300 x 100 metres. Steel rods, each half a metre long, are driven into the ground about one metre apart. They are connected to each other and a cable, and a current is passed through. The different substances in the soil conduct the current differently, showing what is present and where. The signals must be interpreted correctly and any disturbances eliminated, for example electromagnetic pulses from power cables. The results are presented as a 3D graphic which shows the presence of gas and other substances in different colours.
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