Groundwater Exploration Using Resistivity Imaging

The value (or development) of property is often dependant upon the availability of a satisfactory water supply.

Drilling dry holes, or aquiring inadequate water supplies, can be costly and frustrating. The choice of a drilling site therefore, is of the utmost importance and should never be made at random. Before beginning any construction requiring the acquistion of a satisfactory water supply, be absolutley certain such a supply can be obtained.

Apparent Resistivity - What is it?

Apparent resistiviy is the value obtained when current is injected into the soil/rock and the amount of dissipated current is measured therefore leaving us with a resistive (ohm) value for each measurement performed.



Advances in Technology

Since the late 1930s the technolgy of injecting current into the rock/soil and measuring apparent resisitivty has been avaialble. In the last 5 years microchip development and computer processing speeds have dramatiaclly improved and taken us to a new level in the ability to measure subsurface resistive values. We are now able to take muliple resistive measurements, and rapidly process this data using sophisticated software Inversion programs. Measurments that would take months to perfrom can now be accomplished in minutes.

The Power of Inversion

Inversion is the defined as the process of determining the estimates of the model parameter on the basis of the data and the model. Inversion is a mapping from data space to model space and it reconstructs the subsurface resistivity distribution from measured voltage and current data.

Typical Ranges of Resistivity for Some materials

Rock/Material	Resistivity values ?m
Basalt	100- 10,000,000
Limestone	100-10,000
Sandstone	100-1000
Sand/Gravel	600-10,000
Clay	10-100
Unconsolidated wet Clay	20-40
Soil	1-10
Fresh Water	3-100
Native Copper	.0000002