Resistivity imaging is the science of injecting voltage into the ground and measuring current. When this is accomplished using precision scientific instruments, you are able to find high and low resistive anomalies below ground surface. Groundwater would be a very low resistive anomaly.
Technology has advanced to a level that we are able to connect 84 electrodes together using a 1200 meter long cable. A computer directs the instrument to take various readings at different lengths of the survey line. Normally an operator is able to collect approximately 6000 data points in a single line survey. A single line survey can be 300 meters to 1.2 kilometers long. Penetration of survey is normally 15% to 25% the length of the survey line. Example a 1000 meter long survey line would collect data from 150 to 250 meters below grade surface.
Once all data has been collected, it is downloaded into a computer and we process the data using Earth Imager 2D. This program puts the puzzle together and processes the data into a very visual and understandable 2 dimensional graph that clearly shows where the property may or may not produce groundwater.
All of our surveys are completed using the Advanced Geosciences Super Sting R8/ IP resistivity meter and data is processed using AGI EarthImager 2D inversion and modeling software
Link to AGI Site Supersting
http://www.agiusa.com/supersting.shtml
Link to Earthimager 2D software
http://www.agiusa.com/agi2dimg.shtml
Survey cables consist of the main cable housing which incorporates 84 inner cables so that DC current can be injected to independent electrodes. With every injection of current there is a simultaneous reading from 8 other electrodes. The Super Sting Instrument records the amount of current that was injected and received from electrodes.
Each electrode is inserted into ground and backfilled with a Bentonite slurry to increase conductivity of electrical injection.
Survey cable connected to electrode.
The 84 electrodes are connected to the survey line cable and connected to the SUPER STING instrument. Normal length of survey cable is between 400 and 1200 lineal meters. Depth of data collection corresponds to the length of the survey line. The longer the survey line the deeper the data is collected.
Typical Geophysical survey cable line layout plan. Each line was 1200 lineal meters in length.
Example of final data:
Links to case Studies:
Groundwater Exploration Techniques:
https://www.agiusa.com/new_siting_techniques.pdf
Water bearing fractures in bedrock:
https://www.agiusa.com/brochure_waterfracture.shtml
Geotechnical soil investigation for bridge stability
https://www.agiusa.com/brochure_bridgefoundation.shtml
Contaminate Plume investigations
https://www.agiusa.com/brochure_contaminated_fracture.shtml
Landfill Investigation
https://www.agiusa.com/brochure_landfill.shtml
Downhole Tomography
https://www.agiusa.com/2Dtomography.shtml
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