10. Electromagnetic Induction Methods for Environmental Problems

Authors:
  • DFDavid V. Fitterman
    David V. Fitterman
  • VLVictor F. Labson
    Victor F. Labson
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Abstract
Introduction Electromagnetic methods have a special place in the arsenal of geophysical tools available for environmental investigations. They owe their status to five factors. First, many environmental investigations are concerned with detecting the location of contaminants in groundwater and identifying pathways for contaminant transport. These types of problems boil down to learning as much as possible about the fluids in the pore spaces. Contaminants can modify both the electrical conductivity and dielectric constant of the pore fluid, and electromagnetic and electrical methods are the only geophysical methods that are directly influenced by the electrical properties of pore fluids. Second, electromagnetic techniques are sensitive to changes in geology such as rock type, porosity, grain size, fractures, and clay content. This sensitivity allows electromagnetic methods to be used for geologic mapping, which is of great value in developing geological and hydrological models needed for environmental studies. Third, there is a wide range of electromagnetic equipment available for purchase or rental. Over the past 30 years companies such as Geonics, Zonge Engineering, GeoInstruments, Geophex, Iris Instruments, Geosystems, and others have developed modern, reliable instrumentation making electromagnetic surveys relatively easy to perform. Hopefully, this new found ease of data collection does not lull the naïve and untrained into thinking that these methods are without pitfalls. Fourth, electromagnetic techniques are noninvasive. While drilling is often necessary to unequivocally confirm an interpretation, drilling can worsen an environmental problem by puncturing an intact, buried container, or by producing a high permeability flow path for further contaminant migration. Finally, compared to other geophysical methods and to drilling, electromagnetic techniques are relatively inexpensive due to their ease of use and low labor requirements.

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