As part of its field studies capabilities JDMA offers electromagnetic (EM) ground conductivity mapping services to survey, map and analyze the shallow geological subsurface within a study area. EM instruments measure the apparent bulk ground conductivity of the earth materials beneath the instrument (i.e., how well the earth material conducts electricity at low levels). Different earth materials can have different conductivity values. The apparent conductivity can also be influenced by the saturation level of the underlying materials, by the presence of certain contaminants (such as brines or other saline fluids), or by the presence of buried metallic objects or debris. By comparing the apparent ground conductivity values of a study area (or variations in the conductivity values across an area) JDMA personnel can infer characteristics such as earth material type, coarseness (for aggregate materials), or the presence of buried metallic objects such as storage tanks (UST). Because EM techniques are non-invasive they are ideal for studies over impervious surfaces (such as concrete, pavement, or bedrock) or in areas where ground disturbance is undesirable or prohibited (sensitive natural environments or heritage / cultural areas). Our survey data is georeferenced to ensure accurate integration into a client’s existing GIS network, and reports and data products can be tailored to suit a client’s particular needs. In addition, JDMA often compliments its field geophysical surveys with high-resolution imagery from satellite or unmanned aerial vehicle s(UAV) to provide the most up-to-date information about both the surface and subsurface within a study area.
JDMA has been using EM conductivity meters in field exploration and mapping projects since the mid-1980s. A common application for EM surveys is for the detection and assessment of aggregate (sand and gravel) prospects Clean, aggregate deposits have very low EM conductivity compared to glacial till or fine-textured earth materials. Using a Geonics EM31 conductivity meter on a trailer mount and pulled by a truck or ATV, JDMA field staff can quickly scan areas as large as several quarter-sections to assess the presence and extent of potential aggregate deposits with minimal environmental impact. Other common applications for the EM instruments include the detection of buried metallic objects such as underground storage tanks (UST), utility lines or metal debris, detection and mapping of saline leakage around sewage lagoons and landfills, mapping the presence and extent of soil contaminants at oil & gas wells or industrial sites, and mapping previous land disturbance or archaeological features such as building foundations, historic graves or old industrial sites.
