Electromagnetic Induction (EM) is a surface geophysical technique that delineates areas of subsurface conductivity or resistivity. This method is routinely used for locating underground storage tanks (UST's) or other buried metallic or non-metallic objects, defining shallow karst features such as subsurface voids, or any other type application where electrical properties of the target are different than the surrounding media. EM is a valuable tool to perform cursory or detailed investigations of the upper ~20 feet of the subsurface.
Probably the biggest advantages of using EM are speed and adaptability. Because the instrument is mobile, EM studies are usually conducted in grids where data are collected by walking a series of parallel lines. This allows relatively large areas to be thoroughly investigated much more quickly than with other geophysical techniques. Once the data are collected and combined, results can be viewed in plan or map view. This can be very useful in providing optimum well or boring locations during the geotechnical phase of a project.