Services > Applications > Environmental

Introduction

Environmental monitoring is a relatively new application of airborne geophysics, requiring precise measurement of the geophysical parameters (conductivity, etc.), and high resolution of anomaly size and depth. While EM is used most often for mapping groundwater location and salinity, magnetic surveys have been used to detect buried metallic objects and pipelines, and gamma ray spectroscopy can be used to detect man-made radioactivity.

Saline Water Mapping

The presence of saline water on land, whether ground water or intruding sea water, can be very destructive to natural and agricultural plant life. The high conductivity of such water makes it an excellent target for EM detection.

The Florida Everglades is an example where the high rates of groundwater removal, and the interference with groundwater flow by construction, has led to intrusion of sea water under the land surface, killing the natural vegetation. EM surveys have been used several times to map the limits and depth of the saltwater intrusion, and to document the changes over time.

Saline ground water near the surface is a major environmental hazard in Australia, where large areas of farmland may be ruined by rising saline waters. Airborne EM is being used to map the distribution and depth to the saline water over very large areas, to assist the government in planning control programs.

Brine rising through abandoned oil wells can also contaminate the surface, destroying croplands. Airborne EM surveys have been used in Texas to map the location and source of the more conductive saline water. Simultaneous magnetic surveys served to help pinpoint the buried well casings that may be leaking.

Case Histories Florida Everglades (PDF 3.7 Mb), West Texas Brine (PDF 1.58 Mb), Paleochannels (PDF, 176 Kb)

Freshwater Mapping

Fresh water for consumption is a scarce commodity in many parts of the world, and locating new supplies is a major concern. Airborne electromagnetic surveys can be used to detect freshwater-filled fractures in rock, or sandy paleochannels in the overburden. Water-filled fractures are generally more conductive than the surrounding rock.

Paleochannel aquifers, conversely, are generally more resistive, due to the lower clay content and lower salinity of water in the channel relative to the surrounding soils.

Airborne EM surveys can be used not only to locate ground water, but also to map the soil and rock conditions likely to govern the flow of ground water.

Case History Brazil (PDF 1.59 Mb)

Groundwater Recharge

As well as locating existing ground water, airborne electromagnetic surveys can be used to monitor the changing conditions and the rate at which the ground water is being recharged by rainfall. Conductivity maps are used to estimate water permeability (which is governed in part by clay content), and the permeability is related to the rate of downward flow of recharge water by test measurements on the ground.

Applied to an entire region, these measurements can be used to estimate the total water table recharge rate over a large area.

Case History Recharge Mapping in Australia (PDF 75 Kb)

Site Characterisation

Significant environmental risk has been created by the run-off or leakage of acidic water from mines and tailings ponds. Airborne EM has been used in Canada, Australia, and the United States to detect and delineate this drainage, both on surface and through bedrock. Surveys have located leaks in tailings dams and drainage to surface from abandoned coal mines, as well as drainage through deep structures under a lake - undetectable by surface sampling.    

Case Histories Site Characterisation (PDF, 1.39 Mb), Tailings Pond , Characterisation of an Industrial Site in the Canadian Arctic (PDF, 624 Kb) , Contaminant Mapping (PDF, 291 Kb)

Unexploded Ordnance (UXO) Detection

Unexploded ordnance (UXO) can be found in many military ranges and former combat zones. As urban development spreads to these formerly isolated sites, it becomes necessary to locate and remove the many thousands of tonnes of ordnance in the near surface. Magnetic surveys flown with multiple sensors at very low altitude can be used to locate much of this ordnance - individual projectiles or multiple impact areas. Airborne coverage of large areas is much faster and lower-cost than ground coverage, and will delineate areas for ground follow-up.

Case History Aerial Mapping for UXO Detection (PDF 185 Kb)

Radioactive Hazard Detection

The broad spectrum of gamma ray energy measured by exploration systems can also be used to detect energy from many man-made radioactive isotopes, such as Cs¹³⁷ and Co⁶⁰. Surveys have been flown to detect "lost" radioactive smoke analyzers, military radiation sources, fallen satellites, and fall-out from nuclear accidents. Radiometric surveys have also been flown over nuclear facilities and planned uranium mine sites, to map existing background levels for future reference. Airborne surveys provide high-speed coverage, quick response times, and can be used for regional mapping or quick target location.