I want to add some information I received from another source that explains the fundamentals of earth resistance testing for establishing earth grounds. The article covers several of the testing methods and presents the theory why earth resistance is low (conductivity is high).
Earth Ground Testing
Page 8, Figure 9 states the decreasing resistance is based upon increasing concentric shells. In other articles, the terms "sphere of influence" and "hemisphere of influence" are used to describe the same reason for decreasing resistance. Old telegraph engineers used to say earth conductivity (near zero resistance) was because the earth acted as an infinite number of parallel resistors. The use of concentric shells or hemispheres to explain low resistivity is a new twist on that theory.
I have been searching geoscience and geophysics sources for tests that should confirm the theory, but have yet to found any. I find many articles where scientists are exploring the conductivity of various crustal layers, but this seems a mute point to explore if the power transmission system identified in the first post encounters essentially zero resistivity.
