Environmental & Engineering

Overhauser Magnetic Data (.022nT Sensitivity)

Magnetics are one of the most commonly employed methods in environmental and engineering site audits, remediations, and assessments.

The high level of use in industry, research and teaching reflects the versatility, efficient data acquisition, ease-of-use, and effectiveness of magnetics for various types of applications.

Availability of results in the field make magnetics ideal for rapid reporting to clients.

Environmental & Engineering Applications

Some of the typical applications include locating:

Abandoned well casings
Brownfield site surveys prior to trial pits
Boundaries of landfills
Buried drums
Buried reinforced concrete slabs
Buried waste & landfill
Karsts, sinkholes and mineshafts
Pipelines and utility cables
Underground storage tanks (USTs)

Geologic mapping of soils is another application that is increasingly feasible with higher sensitivity magnetometers, and highly sampled datasets. The key to the use of magnetics is the ability to quickly find buried ferrous objects (related to human activity) that threaten the environment. This requires a basic level of experience in equipment operation as well as knowledge of different types of environmental and engineering targets, and the types of anomalies to expect from each target.

Typical buried objects are located in a Magnetic Test area at York University

Generally, environmental and engineering targets provide large and definitive anomalies as they are located near surface. However, they may be affected by cultural noise and near surface debris. These effects are mitigated by use of a gradiometer (i.e. configuration with two sensors). Gradiometers remove much of the unwanted “noise” and are ideal for locating the edges of buried objects. They also enable removal of diurnal effects – thereby eliminating the need for a separate base station.

Detailed Surveying can be accomplished on the ground and with gradiometers, now UAV surveying is possible for rapid investigations

Applying Advanced Magnetic Technologies

As noted above, the gradiometer has much greater near surface resolving power compared to the single sensor, total field magnetometer. This makes this type of configuration an ideal tool for locating small targets. For effective application, a gradiometer requires two or more sensors with high sensitivity, stability and absolute accuracy. The instrument must also measure gradient values simultaneously at two sensors. Sensor and measurement architectures are important considerations for professionals considering a magnetometer purchase.

For environmental and engineering applications, the Overhauser magnetometer/gradiometer is an excellent choice, not only because of its high sensitivity (0.015 nT/ÖHz). Other advantages are the absolute value of the measurement and the inherent stability of counting mechanisms.

Another option is the new optically pumped Potassium magnetometer. The Potassium GSMP-35/25 is a very high sensitivity system for very advanced work, resolution and vehicular surveys. It also has high gradient tolerance for working in areas that may be affected by cultural noise.

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