Near-Surface Geophysical Methods: GPR VS EM

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Whether planning for plant expansion, locating subsurface utilities, or mapping a contamination plume, manufacturers, mining, and other industrial operations are often in situations to investigate subsurface conditions. But, site conditions often vary, suiting one technology more than another.

Two prominent technologies for subsurface investigation are Ground Penetrating Radar (GPR) and Electromagnetic Induction (EM). 

Ground Penetrating Radar Surveys

Ground Penetrating Radar (GPR) has been successfully used to identify subsurface structures by colleges, universities, hospitals, oil and gas production operations, excavating contractors, surveyors, engineering firms, environmental firms, and private homeowners. It is frequently used to identify the following:

  • Subsurface utilities, such as electric, water, sewer, gas, and communication lines
  • Landfill delineation
  • Cemeteries and unmarked burials
  • Underground Storage Tanks (USTs)
  • Underslab voids
  • Frost depths, for construction purposes
Electromagnetic Induction Surveys

Electromagnetic Induction (EM) Surveys are utilized in many different near-surface applications, including geologic, engineering, and environmental investigations. These surveys have been used for mapping shallow soils, soil salinity mapping, shallow groundwater investigations, and the detection and delineation of waste pits or lagoons and associated subsurface contamination from acids, salts, or volatile organic contaminants.

Other applications include the detection of conductive materials, such as clays and ferrous mineral deposits, and resistive materials such as sand and gravel deposits. These systems have also been used in near-surface investigations to detect buried metallic objects, such as drums, tanks, large-diameter utilities, and other non-descript metal objects.

What are the Advantages?

The most obvious advantage of EM surveys is the portability and lightweight nature of the instruments, which can be used on a much more wide variety of terrain than GPR instruments. Also, integration with a GPS device records location simultaneously with the instrument readings. This allows data to be collected quickly and easily mapped without needing a preliminary grid pattern, which is required with GPR.

GPR is a cost-effective and easily deployed method of accurately locating subsurface objects composed of concrete, metal, steel, or plastic. Its capability in locating underground structures is not limited to only metallic objects.

Which is Appropriate for your Project?

Both EM and GPR surveys have risen in use over the last several years, primarily as means of non-destructive subsurface sensing technology. Our staff is trained in both technologies and would be happy to assist you in determining the most appropriate for your project, considering the limitations of site conditions and budget. Contact Jeff Simsa, C.P.G. to learn more.