Here you will find the 3 most popular types of wells [water well types] can be found in the US.
Dug or Bored Wells
Dug or bored wells are holes dug in the ground using a hand shovel or a high-powered piece of equipment like a backhoe. The hole is dug to reach the aquifer/water table until the incoming water exceeds the digger’s bailing rate. The wells are often cased (lined) with bricks, stones, tiles, or other kinds of materials to prevent collapse. They are then covered with a cap of stone, concrete, or wood.
These types of wells are usually dug in areas with soft or less-permeable materials like very fine silt, sand, or clay. They are not dug deeper than the water table because they keep filling up with water. Bored wells, however, can go deeper, much beneath the water table because of the way they are constructed.
Generally, though, both hand-dug and bored wells are shallow (typically around 10 to 30 feet deep), have a large diameter, and usually lack continuous casing (not cased continuously) and grouting which makes them highly susceptible to contamination from nearby agricultural or industrial sites. They also go dry during droughts when the water table drops beneath the well bottom.
Driven wells are created by hammering or driving a small-diameter pipe deep into the ground until it reaches an aquifer (the water table) to draw water from. Like dug or bored wells, they are dug in soft earth like gravel or sand where the aquifer is near the surface. A screen is normally attached to the bottom end of the pipe/casing before driving to help filter out sand and other particles.
These wells are fairly simple and economical to construct, and most are usually cased continuously. The hand-driven wells are typically around 30 feet deep while the machine-driven wells tend to be 50 feet deep or even more, so they are slightly deeper than the dug wells – they are not more likely to get contaminated like the hand-driven wells.
Even so, they still draw water from shallow water tables/aquifers which are near the surface and they are often not really sealed with grouting material meaning contamination can still occur from nearby surface sources/pollutants.
Drilled wells are constructed using rotary-drilling machines or a cable/percussion tool. Due to how deep they go, they are usually reinforced with a metal or plastic casing around the hole to protect the groundwater from contamination and also to prevent the well from collapsing.
The space around the casing is equally sealed with grouting material of bentonite or neat cement to as well prevent contamination by water that drains from the surface downward around outside the casing. Often a pump is also placed in the well up to some depth to help draw the desired water up to the surface.
Of the three types of wells, the drill wells are the deepest – they are typically between 100 and 400 feet deep, and others even go more than 1,000 feet deep. Most modern drill wells require a relatively complicated and expensive drill rig to create. Nonetheless, they have the lowest risk of getting contaminated mainly due to their depth and the fact they have a continuous casing.