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