Electromagnetic Induction
Electromagnetic (EM) methods employed by AGS are useful for locating and delineating:
- Landfill boundaries and cells
- Contamination plumes
- Unexploded Ordnance (UXO)
- Buried metal objects, USTs, and storage drums
- Buried foundations
- Utilities and pipes
- Previously excavated and back-filled areas
EM is a geophysical method based on the physical principles of inducing and detecting electrical current flow within geologic strata. EM induction surveys work by inducing time-varying magnetic fields into the ground from a transmitter coil. The resulting secondary electromagnetic field set up by ground conductors is then measured at a receiver coil. The presence of metals, ions, or clays increase the ground conductivity. Depth range of EM instruments is a function of the degree of separation between the transmitter and receiver coils.
Advantages
EM equipment utilized by AGS is lightweight and easily transportable. Data for a large area can be collected rather quickly. The topography can be uneven and can be covered with higher vegetation.
Limitations
Interference from surface or near surface metallic objects. Sources of interference can include: buildings, metal fences, vehicles, buried pipes and cables, large metal objects and overhead electrical wires. While these objects may interfere with certain types of investigations, EM can be used successfully to map their locations as well.