The interpretation of timelapse geophysical data has qualitative and quantitative aspects. In many cases we know the dominant processes at a location (for instance, this may be movement of water with a higher or lower electrical conductivity from a river into an aquifer, or the injection of an amendment with a high electrical conductivity). An example of the latter is discussed on this website in a summary of a Department of Defense (DoD) ESTCP funded demonstration/validation effort of electrical geophysical monitoring at the Brandywine site in Brandywine, MD.
We can often qualitatively interpret the changes in electrical conductivity as representing these processes. In order to go to quantitative interpretations we need to use some kind of theoretical or experimental petrophysics function which can relate electrical properties to e.g. porosity or saturation. One of the commonly used ones is Archie's law which is discussed here