Boring for Water

The issue of subsurface impediments like strata of oversized boulders/cobbles that cause refusal can not readily be determined in a small localized area from the surface. There are geophysical methods to map the subsurface, such as electrical logging and wave refraction tests, that can be performed from the surface. However, they must be correlated. Sometimes you can do some cheaper probing tests if shallow enough, like CPT methods. However, these are limited by soils densities, tend to be relatively shallow, less than about 200 feet, and can hit refusal also. On the plus side CPT can be accomplished very fast, with many feet probed in a day (thus multiple locations can be tested). It can show the potentiometric water surface when encountered, the soils encountered and densities. Plus with special adaptors it can return some basic information on water quality. downside is that you need to be accessible, but the rigs are smaller and more stable than drilling rig, which means where you can conduct a CPT probing you may be able to drill from an access stand point. I would start with a good geologist experienced in geophysical techniques and local depositional knowledge. They can sometimes have a general idea of what to expect from the surface topography, general depositional trends, etc.. and then develop a program of geophysical testing to locate best areas to drill, followed by direct probing and possible water quality testing (like e-logging and direct sampling), before locating a production well.