Ground Geophysical Surveys


Simcoe Geoscience’s specializes in conducting ground geophysical surveys to complement environmental, geotechnical engineering and exploration projects. Geophysical surveys are deployed to provide physical properties of the subsurface, which could only otherwise be obtained through intrusive inspection or excavation. Geophysical investigations can provide substantial cost savings when compared to traditional blind site investigations as the risks of unknown site issues are vastly reduced. Our clients include the environmental agencies, engineering consultancies, municipalities and property developers. Please contact us for a custom solution.

Applications

Electromagnetic method is a geophysical technique based on physical principles of the inducing and detecting electrical current flow within geological strata. A primary alternating electric current of known frequency and magnitude is passed through a sending coil creating a primary magnetic field in the space surrounding the coil, including underground. The eddy currents generated in the ground in turn induce a secondary current in underground conductors which results in an alternating secondary magnetic field, that is sensed by the receiving coil. The secondary field is distinguished from the primary field by a phase lag. The ratio of the magnitudes of the primary and secondary currents is proportional to the terrain conductivity.

The readings are commonly expressed in the conductivity units of mS/m. The depth of penetration is governed by the coil separation and orientation. The EM method should not be confused with the electrical resistivity method. The difference between the two techniques is in the way that the electrical currents are forced to flow in the subsurface. In the electromagnetic method, currents are induced in the subsurface without any direct contact with the ground surface.

EM surveys are categorised as frequency domain and time domain. Frequency domain instruments measure the amplitude and phase of the induced electromagnetic field while time domain instruments measure the decay time of the induced field. The applications of this method include:

  • Contaminant mapping
  • Permafrost identification
  • Soil characterization
  • Groundwater investigation
  • Identify karst bedrock features
  • Predict areas prone to slope failure
  • Underground storage tank (UST) detection
  • Identify small ferrous and non-ferrous metallic
  • Map soil salinity and salt water intrusion
  • Delineate landfill and trench boundaries
  • Detect location and orientation of faults
  • Map lateral and vertical distribution of soil type
  • Defining the lateral extent of potential aggregate resources

Technologies

Ground Conductivity Meters
  • EM31-MK2
  • EM34-3
  • EM38-MK2
Metal Detectors
  • EM61-MK2A
  • EM61S
  • EM61HH-MK2A
Time Domain Systems
  • ABEM WalkTEM
  • GDD NordicEM24

Applications

The purpose of electrical surveys is to determine the subsurface resistivity distribution by making measurements on the ground surface. From these measurements, the true resistivity of the subsurface can be estimated. The ground resistivity is related to various geological parameters such as the mineral and fluid content, porosity and degree of water saturation in the rock. Electrical resistivity surveys have been used for many decades in hydrogeological, mining and geotechnical investigations. More recently, it has been used for environmental surveys.

Induced Polarization (IP) method is closely related to the resistivity method. IP method requires measuring instruments that are more sensitive than the normal resistivity method, as well has significantly higher currents. IP surveys are common in mineral exploration and this method is also able to detect conductive minerals of very low concentrations that might otherwise be missed by resistivity or EM surveys. IP method uses alternating currents (in the frequency domain) of much higher frequencies than standard resistivity surveys. Electromagnetic coupling is a serious problem and to minimize the EM coupling, the dipole-dipole (or pole-dipole) array is commonly used.

The common applications of these methods are to:

  • Investigate groundwater sources
  • Characterize soil and rock types
  • Delineate subsurface contaminants
  • Map bedrock topography
  • Investigate the thickness of peat
  • Determine the existence of subsurface voids
  • Identify buried utilities and infrastructure
  • Investigate archeological sites
  • Image geological structures, fracture and fault
  • Delineate potential aggregate resources
  • Complement electrical grounding studies at new and existing pipeline and electrical transmission facilities.

Technologies

Resistivity/Induced Polarization Systems
  • Walcer Model TX KW10
  • GDD IP Transmitter & Receiver

Applications

Ground penetrating radar (GPR) provides a high resolution, cross-sectional image of the shallow subsurface. A short pulse of electromagnetic energy is radiated downward. When this pulse strikes an interface between layers of material with different electrical properties, part of the wave reflects back, and the remaining energy continues to the next interface. Depth measurements to interfaces are determined from travel time of the reflected pulse and the velocity of the radar signal.

The Ground Penetrating Radar (GPR) method relies on contrasts in the dielectric constant between materials. The methods have been used extensively to:

  • Map water table and bedrock topography
  • Map stratigraphic layers
  • Evaluate mine and quarry rock
  • Image geological structures, fracture and fault
  • Map the location and burial depth of drums, underground storage tanks, and utilities
  • Identify buried utilities and infrastructure
  • Delineate disposal pits, trenches, and landfill boundaries
  • Locate voids and washouts along pipelines, under roadways, parking lots, and building floors
  • Investigate the thickness of peat
  • Determine the existence of subsurface voids
  • Investigate archaeological sites and cemeteries
  • Screen proposed borehole locations for subsurface interference
  • Delineate inorganic and organic free-phase contamination plumes

Technologies

Ground Penetrating Radar Systems
  • StructureScan™ Mini HR
  • UtilityScan® DF &UtilityScan®
  • RoadScan™ 30
  • BridgeScan™

Applications

Seismic survey, method of investigating subsurface structure, particularly as related to exploration for oil & gas, mineral deposits and geotechnical studies. The technique is based on determinations of the time interval that elapses between the initiation of a seismic wave at a selected shot point and the arrival of reflected or refracted impulses at geophones. Seismic waves are generated using various sources such as hammer, drop weight and dynamite, depending on the survey configuration. Upon arrival at the geophone, the amplitude and timing of waves are recorded to give a seismogram. Reflection and Refraction are the most commonly used seismic techniques. Multichannel Analysis of Surface Waves (MASW) is relatively new addition to the seismic methods and evaluates ground stiffness in 1-D, 2-D, and 3-D formats for various types of geotechnical engineering projects.

Seismic methods determine geological structure and rock velocities by either refracting or reflecting waves off boundaries between rock units with different seismic velocities or impedance, the common applications include:

  • General geologic structure
  • Mapping of bedrock depth and topography
  • Overburden thickness
  • Water table depth
  • Faults and mapping of weak zones
  • Rock velocities and quality
  • Geologic layering
  • Landfill investigations
  • Rock rippability and quality
  • Engineering properties: bulk or shear moduli

Technologies

Seismic Solutions
  • ABEM Terraloc Pro

Applications

Magnetic surveys measure small, localised variations in the Earth's magnetic field. The magnetic properties of naturally occurring materials such as magnetic ore bodies and basic igneous rocks allow them to be identified and mapped by magnetic surveys. Strong local magnetic fields or anomalies are also produced by buried steel objects. A broad range of applications of ground magnetic surveys are:

  • Accurately mapping archaeological features
  • Mapping basic igneous intrusive rocks & faults
  • Evaluating the size and shape of ore bodies
  • Identify geologic bedrock features such as mafic dikes or geologic contacts
  • Delineate areas of ferromagnetic
  • Finding buried steel tanks and waste drums
  • Detecting iron and steel obstructions
  • Locating unmarked mineshafts
  • Locate underground storage tanks (USTs)
  • Locate buried drums
  • Delineate landfill perimeter
  • Identify locations of historic structures

Gravity surveys measure the changes of rock density by looking at changes in gravity caused by geological structures. State-of-the-art gravity meters can sense differences in the acceleration (pull) of gravity to one part in one billion. Measurements taken at the Earth’s surface express the acceleration of gravity of the total mass of the Earth but because of their high sensitivity the instruments can detect mass variations in the crustal geology. The amplitude of the variation from the high to the low of the gravity gradient zone is a function of the displacement on the fault. In addition to providing insights to fault problems, gravity methodology applies to any geologic problem involving mass variations. The common applications of gravity survey are:

  • Mineral Exploration - massive sulphides, porphyry's structure
  • Diamond Exploration - Kimberlitic pipes
  • Coal Exploration - basin structure, grabens, large faults
  • Petroleum - frontier basin mapping, diapirs
  • Locating void(s) in Karst Topography
  • Engineering, tunneling, footings

Technologies

Ground Magnetic Systems
  • Overhauser magnetometer system
  • Optically pumped Potassium magnetometer and gradiometer systems
  • Proton magnetometer system
Ground Gravity Systems
  • LaCoste& Romberg Model G Aliod1000
  • LaCoste& Romberg Model G Land meter

Applications

Borehole logging is the practice of making a detailed record (a well log) of the geologic formations penetrated by a borehole. The geophysical logs are the physical measurements made by instruments lowered into the hole. Logging tools measure the natural gamma ray, electrical, acoustic, stimulated radioactive responses, electromagnetic, nuclear magnetic resonance, pressure and other properties of the subsurface and their contained fluids. Well logging is performed in boreholes drilled for:

  • Mineral Exploration
  • Environmental and Geotechnical Studies
  • Groundwater Exploration
  • Geothermal Exploration
  • Oil and Gas Exploration

Technologies

Borehole Logging Systems
  • Natural Gamma
  • Spectral Gamma
  • Electrical Resistivity
  • Induced Polarization
  • Natural Gamma