induce currents into the ground which generate magnetic fields whose
strength is a function of the terrain conductivity. The transmitter
and receiver coils do not contact the ground thus allowing for rapid data
collection in most climatic conditions and terrains. A Geonics EM-31
has an effective depth of investigation of about six meters and a Geonics
EM-34 uses three variable depths of exploration down to about 60 meters.
Data are typically presented as conductivity profiles or as contoured
apparent isoconductivity maps.
ECHOTECH has combined these precision instruments with a real-time
sub-decimeter differential global positioning system (GPS) and designed a
non-conductive deployment trailer system which allows us to collect continuous
EM-34 data over large acreages very rapidly. We have successfully
collected data at rates as fast as 15 miles per hour and maintained production
rates of over one square mile per day!
This isoconductivity map highlights hydrocarbon contaminated soils at an
abandoned jet fuel refinery. The more conductive soils (blue) are
indicative of bioremediation of the petrochemicals.