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I posted this question on Engineering Stack Exchange as well. I'm not sure if here or there is the better place. There is no agriculture stack exchange (much as I wish there was) so I am posting there as well as here.

I need to choose where to drill an agricultural well. I am trying to get as much water as possible (at least 100 gpm).

I am considering hiring a guy who claims to be able to find water using a device called an ABEM WADI. My understanding is that this devices uses VLF signals from far away transmitters to identify fractures in the ground. He says he walks in a straight line in a candidate area for well drilling, and looks for fractures noted on the screen of the WADI. He claims that areas with a certain type of fracture (I think he said 45° fractures were the best) are more likely to yield a lot of water.

To what extent is this method scientifically valid? It sounds legit, but methods of "dousing" or "witching" for water are often little more than divination, so I'm skeptical. I googled around and found some scientific papers about VLF-EM scanning, but I lack the science/engineering chops to interpret them.

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VLF-EM is a perfectly valid technique for helping an expert decide where best to locate wells in geological environments where water is largely flowing in fractures. Typically it is a useful technique in fractured bedrock where a successful water well needs to intercept connected fractures or fissures. In other geologies, for instance porous sandstones, it would be much less useful. Drilling for water in fractured terrains is always a slightly risky proposition; geophysical techniques help site wells to intercept fractures but they can't guarantee yields, which will depend on how large the fractures are and how interconnected they are. A reputable contractor should be prepared to provide references from satisfied clients and that is a good starting point.

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