Geophysical methods provide a non-invasive, non-hazardous, cost-effective method for delineating subsurface contaminant plumes in certain conditions. Integrating these tools into contaminated site surveys reduces the number of boreholes needed to characterize the site and simultaneously provides more spatial coverage in reduced time (and therefore cost). Using geophysical tools this way also minimizes operator exposure and thereby enhances personnel safety.
Electromagnetic Tools
The “EM-31” can provide measurements of apparent conductivity down to approximately 6 meters. Other tools such as the EM-34 can reach as deep as 60 meters as required. Data processing and interpretation can often correlate the measurements with the presence of contaminants including hydrocarbons and other, potentially relevant, subsurface features such as buried structures. We’ve had success throughout Alaska identifying contaminant fate and transport over various soil types and conditions.
The figure on the left shows the measured conductivity response in a potentially contaminated area. A subsequent drilling an sampling campaign found elevated amounts in precisely the regions that the geophysical interpretation identified!
GPR data indicating presence of hydrocarbon contamination (brown)
Ground-penetrating radar (GPR) will often detect subsurface contaminants such as hydrocarbons (oil, gasoline, etc) and chlorinated solvents (TCE, PCE, for example) because those contaminants tend to be more or less conductive that the groundwater, depending on their type and age. Other factors include contaminant concentration, depth, and soil types. Interpretation of GPR can also produce maps of subsurface geology as an indication of the potential flow pathways of the contamination in the ground. This tool is easily implemented in Arctic conditions, and can simultaneously produce information about other site conditions such as aquifers or buried ice lenses.
Electrical Resistivity Imaging
Electrical resistivity methods are often able to map subsurface contamination by measuring the difference between the background conductivity and the conductivity of the contaminated areas. This tool works well for contaminant plumes emanating from landfills and for leachate plumes from geotechnical work such as mining.
