Introduction

Electrical properties are among the most useful geophysical parameters in characterizing earth materials.  Variations in electrical conductivity (or its inverse, resistivity) typically correlate with variations in water saturation, fluid conductivity, porosity, permeability, and the presence of metal.  Depending on the particular site, these variations may be used to locate contaminant plumes, salt water intrusion, stratigraphic units, sinkholes, fractures, buried drums and tanks, and any other feature whose electrical properties contrast with the surrounding earth. 

Ground conductivity can be measured either directly, using the galvanic resistivity method, or inductively, using electromagnetic induction (EM). Because EM requires no direct contact with the ground surface, data can be acquired more quickly than with resistivity.  Resistivity, however, can provide better vertical resolution and is generally less sensitive to cultural noise such as fences, buildings and overhead powerlines.