Mapping Subsurface Soil Conductivity
Using Electromagnetic Induction (EM) Surveys
What Are the Applications?
Electromagnetic Induction (EM) Surveys are utilized in many different near-surface applications including geologic, engineering and environmental investigations. These surveys have been used for mapping shallow soils, soil salinity mapping, shallow groundwater investigations, and the detection and delineation of waste pits or lagoons and associated subsurface contamination from acids, salts or volatile organic contaminants.
Other applications include the detection of conductive materials, such as clays and ferrous mineral deposits, as well as the detection of resistive materials such as sand and gravel deposits. These systems have also seen use in near-surface investigations for the detection of buried metallic objects, such as drums, tanks, large diameter utilities and other non-descript metal objects.
What are the Advantages?
The advantage of EM surveys is the portability and lightweight nature of the instruments. Also, integration with a GPS device records location simultaneously with the instrument readings. This allows data to be collected quickly and easily mapped without having to lay out a preliminary grid pattern, which is required with other methods.
In addition, some instruments are capable of recording up to three frequencies simultaneously, which provides a profile of the instrument readings at different depths.
Likewise, there are limitations. In order to be detected, the electromagnetic properties of the target(s) of interest must contrast those of the surrounding soils. In addition, the depth of investigation of these instruments can be limited to approximately 20 feet or less, depending on site conditions and equipment. More sophisticated EM instruments are able to reach depths of 100 feet.
Interested in learning more about EM Surveys? Contact Jeff Simsa, C.P.G., P.G.
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