Water Well Information
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A water well is a lot more than a drilled hole, but for many people, the above ground part of the drilling process is the only part they see. A water well is a specially engineered hole in the ground.

Drilling Diagram

Great skill is needed to guide and control a water well drill as it penetrates sand, gravel, clay and solid rock formations deep underground. There are often several rock layers in a single well; each may need different drilling pressures. Once water is encountered, the driller will need to keep a close watch on the drilling process.

Most home wells are drilled to 8 or 6 inches in diameter. Municipal or irrigation wells are likely to be drilled at larger diameters, sometimes as much as 24 inches or more.

In rotary drilling, a drill bit is attached to a length of connected drill pipe. The drill bit will be made of tough metals such as tungsten, and as the drill is rotated, the bit acts to grind up the rock. The broken pieces are flushed upward and out of the hole by circulating a drilling fluid down through the drill pipe and back to the surface. This drilling fluid also serves to cool and lubricate the drill bit, and by stabilizing the wall of the hole, it can prevent possible cave-in of unstable sands or crumbly rock before the well casing or well screen is installed. As the drill intersects water bearing rock formations water will flow into the hole. Most drillers carefully monitor the depth of water "strikes" and keep a note of the formations in which they occur.

The top part of the well is usually lined with steel or plastic well casing. The diameter of the drilled hole is usually an inch or two wider than the diameter of the casing. The space between the drilled hole and the casing has to be filled to prevent the chance of polluted surface water from migrating downward along the outside of the casing where it might contaminate the aquifer. This filling is called "grout" and it may be either cement or special volcanic clay called bentonite. Sometimes most of the space is filled with the fine rock pieces from drilling and then the top 20 feet is grouted.

Many well owners know little or nothing about their wells. All they see is a foot of so of well casing sticking out of the ground.

Water System Installation

Water wells come in all shapes and sizes and need to be designed to suit the geologic conditions, the purpose for needing the water and to comply with local regulations. A water well must be deep enough to reach the saturated rocks or sediments in the aquifer. In low yielding rocks the well may be drilled several hundred feet deeper than the level of ground water in order to provide some water storage in the well column. (One hundred feet depth in a six-inch diameter well below the water table stores 150 gallons of water.)

The well's diameter must be large enough to take the pump equipment necessary to move the water to the surface. Most home wells use four-inch diameter pumps. The well casing lining the drilled hole must extend down far enough to reduce the risk of any surface or near surface contamination. The well may need a screen to allow for the efficient flow of water from the aquifer into the well. In some cases it may be necessary to place additional casing to seal off parts of the drilled hole where, for example, the water may have high iron content, or some other unwanted chemical attribute.

In many states there are regulatory requirements and construction codes that the well contractor has to follow, particularly concerning depth of casing and grout material used to seal the annular space between the hole and the casing. Critical decisions related to well depth, diameter and positioning of screens (if needed) are usually made on a site by site basis depending on the driller's experience in the local area and on the specific information on water strikes and rock conditions found during the drilling process.

A well screen is an engineered device that may be used in wells to help maximize inflow from the aquifer and allow for long-term satisfactory operation of the well. Well screens are typically installed in wells where the aquifer is comprised of loose or unstable material. The screen prevents rock fragments from entering the well, helps support the wall of the well and allows water to enter slowly. Turbulent flow can more easily transport unwanted rock particles and agitated water may release minerals and clog up the well. For high yield wells a "gravel pack" is sometimes used to fill up the space between the well screen and the drilled hole. Placing the gravel in the well next to the screen can be a tricky business, but the highly permeable gravel can really help make the well efficient.

For wells where freezing temperatures occur, there has to be a way of diverting water from the well to the home below ground. To achieve this, most contractors will use a special adaptor that connects the vertical pipe coming from the well inside the casing to a horizontal pipe that takes water from the well to the home. This connection is usually made about six feet below ground surface by means of a "pitless adaptor". This device not only connects the well pipe to the house pipe, but also helps support the weight of the pump and pipes.

All wells should have a secure cap to prevent insects or debris from entering the well. However, the well cap should not have a perfect airtight seal. There must be an air vent so that when the water level drops because of pumping, the space created by the falling water level can be replaced by air. If a well is constructed in an area prone to flooding the casing should be extended up to above the likely flood level.

For more information on ground water
contact Arkansas Valley Drilling.

600 Canon Ridge Rd., Canon City, CO 81212
toll-free: 877-976-6847 -- local: 719-276-6847 -- fax: 719-784-3894

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