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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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The answer above is wrong. VLF-EM equipment isn't using the VLF signal as 'radar' and looking for scattering. THE VLF signal induces an electromagnetic response in conductive rocks, and the measuring equipment looks for variations in the strength and phase of this response. As such it is useful to hydrogeologists for detecting fractures in terrain where these are water bearing.

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  • $\begingroup$ Thanks for clarifying $\endgroup$ – Andrew Cone Feb 2 at 22:09
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Nope. Here is why:

VLF frequencies have wavelengths between a thousand meters and ten thousand meters. To scatter off a feature with a scale length of order ~1000 meters (like a subsurface fracture) and yield information on the location of the scattering event requires that the wavelength be of order ~1/10th the scale length of the scattering object. This fundamentally eliminates VLF "radar" as a means of locating subsurface fractures with an accuracy of order ~tens of meters.

Ground-penetrating radar is a real tool good for finding underground structures but requires frequencies in the range of 10MHz to 2.6GHz (VHF/UHF to microwave) to work.

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