Sorry, school last night, got in late. The Fall of Potential method is probably one of the simplest tests you can perform. It simply takes the electrode being tested, (let's call it X) adds two electrodes (electrode Y at app. 62' and Z at app. 100') and measures voltage between X and Y, and amperage between X and Z.
The problem Qknowles has is that his "electrode" is MILES long, and to calculate 62% and 100%, it stretches the entire process way out. I would think (big stretch here since I don't have plans or specs for his project) that they could measure FoP individually for each well head, add resistance for conductor, and calculate the difference, but again without a lot more info on his project, that is a BIG shot in the dark.
I hate to gig you on this, but Chap. 6 of the current edition of Soares, it's also in the American Electricians handbook.
I don't have any way of inserting drawings in here, I'll try to scan one in from Soares, it may make it easier to 'see', and send it to you via e-mail.
He also likely has to come up to NICET standards, and even though the test does not change much, it may be quite rigorous. I cannot imagine quite so extensive a test in what I'm guessing is sandy soil, but again, I'm not there. Could be since I possess a broken leg though
. Nice little working vacation, but he'll have to push me around in a wheelbarrow