Electromagnetic Conductivity (EM)

Electromagnetic Conductivity (EMC) is a noninvasive geophysical technique that uses electromagnetic induction.  A transmitter coil induces a magnetic field that creates a current in the ground. The current produces a secondary magnetic field that is sensed by a receiver coil.  Data is collected at individual points spaced evenly along a transect. Typically, signals are received from depths of 15 feet or less using a Geonics EM-31 or EM-61 or from depths of about 70 feet or less using a Geonics GEM 2, multi-frequency EM sensor.

The in-phase component is typically used as an indicator of buried metallic objects.  The quadrature-phase component is typically used as a measure of general ground conductivity.  Readings are compiled to make contour maps using computer mapping programs.

Applications
Use to identify areas of higher conductivity such as landfill cells.  Use in-phase component to identify areas of possible metallic debris.  Can be used to map electrically conductive contaminant plumes and saltwater intrusion.

Qualifications

SEI has been using the EM-31 and EM-61 systems since 1987 to delineate landfill sites and locate buried metallic objects.