Watched the whole video. I like the part where you were showing the change in resistance as you drive down. Once you hit your water table that is where I suspect you saw the impedance go down. I have seen where engineers focus on driving rods 20 or 30 ft to get low resistance. However, I feel it is easier and cheaper to put multiple parallel 10' rods with 10' separation. With that in mind, I wish you would have done 2 or 3 rods starting at 10'. Measure the impedance of each rod, then 2 in parallel and then 3 doing that for each 10'. I believe you would have found being satisfied with 3 rods at 10 feet deep.

Another problem with the fall of potential I have with a digital reader is that while it has an automatic frequency selector for the injection current 75% of the time my unit errors out because it can find a frequency that isn't getting interference. So I always end up using the clamp method.