Resistivity Method
The Resistivity Method is a direct current (DC) electrical geo-survey measurement technique used to determine and map soil and groundwater locations and characteristics. With the Resistivity Method, electric current is passed through two electrodes installed into the ground, called “current electrodes”. As the current is passing through the ground, it also flows through a “spONTaneous electrode” and “potential electrode” connection, distributing electric potential. The degree of the electric potential dissipates is affected by soil and groundwater properties, which in turn are displayed on a chart used to create a map of the subsurface.
Soil and subsurface characteristics that have an effect on the resistivity reading obtained by the Resistivity Method apparatus include porosity, salinity level, clay composition, gravel composition, bedrock composition, water content and any obstruction that is non-conductive (such as roots, rocks or other non-metallic material that could potentially obstruct the electric current).
This method has been widely used for water and oil exploration as well as for soil subsurface/parameter research over the past few decades. The resistivity survey can be tailored to the objectives of the surveys, ranging from shallow to deep exploration with many measurement devices and or array types available to choose from.
The Resistivity Method is useful in many applications, such as locating groundwater or other subsurface elements and mapping subsurface formations. It is also used for archaeological research and for evaluating the polluting potential of hazardous materials in the environment.
The Resistivity Method is a highly effective, versatile, and cost efficient means of investigating subsurface geology. Its advantages include its ability to measure high conductivities (clay and gravel), high resistivities (bed rock and water), and as well minuate variations in data sets. This method is also advantageous in that it is a passive method that creates no environmental disturbance, and is well suited for use in a variety of geological explorations.
The costs associated with the Resistivity Method are very reasonable when compared to other methods of subsurface exploration. The equipment itself is inexpensive and easy to use, and the data can be used to develop a detailed characterization of the subsurface.
The disadvantage of the Resistivity Method lies in the accuracy of the measurements. If obstacles, large boulders, or other nonconductive material are in the path of the electric current, the accuracy of the data can be compromised. Furthermore, two-dimensional (2-D) mapping is limited to shallow mineralization, and so it is useful only for very shallow exploration. Three-dimensional (3-D) mapping may be used for deeper investigations, but is an expensive option that is limited to some areas of soil and groundwater exploration. The Resistivity Method can also be affected by various ambient noise sources, such as alternating current (AC) power sources and other electromagnetic interference (EMI).
Despite this, the Resistivity Method still remains one of the most cost-effective and reliable methods of determining subsurface parameters and mapping the subsurface geology. It is an invaluable tool for various types of geological exploration and is well suited to a variety of applications, including water and oil exploration, soil parameter research, and archaeological research.
