ELECTROMAGNETIC INDUCTION

EMI

In Illinois Soils

• Small electrical charge caused by collapse of a magnetic field is introduced into soil

• Transmitter emits this signal, receiver records the magnitude that moved through the soil

• Receiver measures resistivity and changes to conductivity

• Takes a large number of “borings”

• Soil conductivity is considered to be a soil property

• Soil conductivity is influenced by: moisture content of the soil salt or cation content of the soil amount of clay in the soil type of clay in the soil organic matter content of the soil

• In Illinois, we have used five different tools

VERIS (Veris Technologies Inc.) EM-38 (Geonics Limited) EM-31 (Geonics Limited) EM-34 (Geonics Limited) Dualem (DUALEM Inc.)

EM-31

• Illinois NRCS has one of these• In operational mode, it is about 10

feet long• This separation distance allows for

15-18 feet of apparent depth penetration

• Pedestrian surveys for on-site use and wheeled cart for field use

ILLINOIS USE OF EM-31

• Surficial geology interpretations • Assessing permeability differences

with depth• Separation of soil parent materials • Effluent plumes from animal waste

systems• Salt contamination from oil wells• Mine land reclamation studies

• Use with updating and refining Order 1 and Order 2 surveys:

Find small areas of contrasting conductivity

Fine-tune line placement Assesses broad landscape units quickly Defines areas needing detailed

investigation