When you purchase a lot with the intent of building you generally require that the lot be able to support a septic system (the lot must perc). It is generally though not until after the purchase that you find out whether there is an available underground water source adequate to supply a well. At least in this part of the country, the only way to find out is to drill a well.
I obtained several bids and decided to contract with one that had a package price that included 200 feet of drilling, installing 42' of casing, and the pump and pressure tank (as well as trenching for the electrical connection). I had seen the drilling process on TOH but never for reals, so I was excited when the rig pulled into the driveway.
I found out that these truck cost about $500,000, which seemed like a lot until I saw all the functionality that one includes (which I will try to explain below). We were in the middle of a drought so I was less concerned about the rig crushing my bridge than with previous big trucks even though this one weighed in at 62,000 pounds. I had cleared the piles of timbers so that he could pull the rig into place.
Placement for the well had previously been established by the county environmental health guys so all I had to do was clear out the brush so that the truck could back into place and raise the drilling apparatus.
Once that was raised the operator leveled the truck with hydraulic jacks that automagically came out of the bottom of the truck. There is a complicated looking control panel on the back of the truck from which the operator runs the show.
You can see the 15 pieces of drill rod (each 20' in length) plus 6 more that are already loaded in the carousel (you can see those in the next picture below), which allows a total drill depth of 420' feet. If they don't find an adequate supply of water by that depth they will have to have more drill extensions delivered. Here you can see the drill bit attached to a rod (the whole assembly is sometimes called a string).
Here is a picture of two of the drill bits. Here in the North Carolina Piedmont there is a layer of clay and under that nothing but granite so these bits are good for less than 1000' feet of drilling and then have to be replaced (at something like $1500 each).
In our case the clay layer was only 6' thick. At a depth of about 25' the pieces of granite that were coming out of the hole started to be wet so that meant we had hit the water table. The drill turns fairly slow and on top is an air powered jackhammer type arrangement so the thing drills a 6" hole through granite much faster than I expected (a foot or two per minute). You can see in the following pic that the granite chunks that come up (air is injected through the center of the drill, which blows them right up and out of the hole) look like gravel.
A shroud is placed around the hole so that the mixture coming up out of the ground does not blow all over the bystanders. As we drilled deeper there was more water in the mixture (a good sign indeed).
At 200' (the depth included in the package price we still had less than 2 gallons per minute of flow, which was not enough. According to the chart we would need 300' of storage capacity if the flow was less than 3 gallons per minute so I agreed that we needed to drill deeper. At 300' we measured it at 4 gallons per minute, which I though would be enough since we plan to store rainwater collected from the roof for both the greenhouses and the garden.
Casing pipe was inserted to a depth of 42' to keep groundwater from entering the well and a submersible pump was set at about 20' from the bottom. The next day the well was grouted and the pressure tank put in place. Now if only we had some electricity to run it with!