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How Are Boreholes Drilled?

Boreholes

1. Water well types

   A borehole is a hole bored into the ground to collect samples for analysis or to extract oil or water. Boreholes range from extraction of ice cores from glaciers to digging water wells.

   Water wells

2. A water borehole can be dug, driven or drilled. To dig a water well, the ground must be soft enough to dig and the water table shallow enough to avoid collapse of the soft walls. Soil can be hauled up by bucket supported with a tripod. Metals rings and braces are placed against the walls to prevent collapse during excavation.
   Driven wells are created by pounding the top of a pipe with a weight. The configuration has three pieces. A rotary bit, or drive point, attached to the bottom of a short pipe rotates as it is pounded from above. The short pipe may have a screen over perforations, so that water can flow in when the aquifer level is reached. The short pipe’s diameter at the top is tapered, so the well pipe can fit onto it. A rod of narrower diameter, called a guide rod, fits inside the two pipes. It is weighted from above, and drops down onto the rotary bit.
   Another method is to jet water through a narrow pipe into the bottom of the hole, where a wide drill bit has loosened soil to be carried back up through the wider channel on the outside of the pipe. This is called a jetted well.
   A variation of the jetted well is to use a percussion bit to loosen earth, while pouring in water. When the resulting paste is too thick to allow the bit to solidly hit earth, the percussion bit is lifted out and a bailer is lowered in, to remove the liquid.
   Drilling requires a drill rig, which are often mounted on trucks. Drill bits can be alternated between rotary and percussion type (to break hard rock). A rotary auger bit may be needed close to the surface to lift out soft soil.
   Highly detailed instructions for various methods of drilling wells can be found at the Life Water International link listed in resources.