What is Induced Polarization (IP)?

IP stands for “Induced Polarization”. IP measures the chargeability of the ground, in other words how does the voltage of the ground react when a current is applied and removed.

Typical applications where IP investigation is commonly used include:

  • Mineral prospection, for identification of mineral seams and ore bodies
  • Hydrogeophysical characterization, including clay / groundwater discrimination and saline intrusion studies
  • Landfill characterization, determining dimensions and potential leakage
  • Peat stratigraphy and permeability
  • Contamination plume monitoring, such as hydrocarbon spills, bioremediation, acid rain percolation through organic waste, and studies of saline wastewater.

The chargeability of subsurface materials is essentially an electrochemical effect caused by several different phenomenon. The main controlling factors are pore fluid composition, pore space characteristics, grain size and the type of charged particles present within the investigated volume. Chargeability is often presented in units of mV/V; in simplistic terms this is stating how much voltage the ground holds onto when a current is removed compared to the voltage when that current was actively flowing. Higher values indicate higher chargeability – i.e. a larger IP effect.

It is understood that there is a large overlap in resistivity values for different materials, which can make a ‘blind’ geological interpretation tough. But adding the chargeability values gained from an IP investigation, can make it easier to differentiate between some of these materials, due to their differences in chargeability.

For instance:

  • Fresh water has a higher chargeability than salt water
  • Fresh water has a lower chargeability than clay
  • Very high chargeability associated with certain mineral deposits

IP measurements should be made with ordinary resistivity equipment’s, as Terrameter LS 2 and can be collected during the same measurements cycle as the resistivity data. This will give you an extra data set, without any considerable increase in measurement time.

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