Electromagnetics

 

Electromagnetic and electrical methods are commonly used in environmental and ground water studies. These methods delineate contamination, detect buried objects, and quantify aquifers. These methods detect differences in electrical properties between rock, soil, and buried objects. Information is collected rapidly, providing an economical means of surveying large areas.

 

Time Domain Electromagnetics

Time domain electromagentcs, TEM,  (also referred to as transient electromagnetics) measures the changes in electrical resistance with depth.  The TEM method involves pulsing a magnetic field which induces eddy currents in the ground.  The eddy currents create a secondary magnetic field that decays with time.  The rate of decay is related to the resistivity of the formations below.  Clay is a good conductor of electricity.  Poorly sorted saturated sands and gravels are moderate conductors of electricity.  Dry sands, gravels, and consolidated rock are poor conductors of electricity.  The resistivity of a formation goes down as the salinity of the pore fluid goes up.  Measuring electrical resistance with depth determines if clays or high salinity pore fluids are present.  Advantages of TEM methods include quick setup time, portability, and significant ground penetration when compared to other resistivity techniques.

 

Electromagnetic Terrain Conductivity

Electromagnetic terrain conductivity meters map conductive objects or areas below the ground surface. Terrain conductivity meters are light, portable, and can cover large areas quickly. They are particularly useful in mapping regions containing conductive contamination. Electromagnetic techniques are used to:

  • Locate buried metal objects
  • Delineate near surface contamination plumes
  • Map buried trash cells and pits
  • Define lateral changes in lithology

At J R Associates we stand ready to apply our geophysical expertise to your particular requirements. Please contact us to discuss how our combination of techniques, knowledge and experience can provide you with a window on what's underground.

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J R Associates, 1886 Emory Street, San Jose, CA  95126

Ph: (408) 293-7390 Email: jra@Greatgeophysics.com