Types of Wells
Planning for a Well
Types of Wells
Drilled wells. Drilled wells are constructed by either cable tool (percussion) or rotary-drilling machines. Drilled wells that penetrate unconsolidated material require installation of casing and a screen to prevent inflow of sediment and collapse. They can be drilled more than 1,000 feet deep. The space around the casing must be sealed with grouting material of either neat cement or bentonite clay to prevent contamination by water draining from the surface downward around the outside of the casing.
Driven wells. Driven wells are constructed by driving a small-diameter pipe into shallow water-bearing sand or gravel. Usually a screened well point is attached to the bottom of the casing before driving. These wells are relatively simple and economical to construct, but they can tap only shallow water and are easily contaminated from nearby surface sources because they are not sealed with grouting material. Hand-driven wells usually are only around 30 feet deep; machine-driven wells can be 50 feet deep or more.
Dug wells. Historically, dug wells were excavated by hand shovel to below the water table until incoming water exceeded the digger's bailing rate. The well was lined with stones, bricks, tile, or other material to prevent collapse, and was covered with a cap of wood, stone, or concrete tile. Because of the type of construction, bored wells can go deeper beneath the water table than can hand-dug wells. Dug and bored wells have a large diameter and expose a large area to the aquifer. These wells are able to obtain water from less-permeable materials such as very fine sand, silt, or clay. Disadvantages of this type of well are that they are shallow and lack continuous casing and grouting, making them subject to contamination from nearby surface sources, and they go dry during periods of drought if the water table drops below the well bottom.
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A drilled well consists of a hole bored into the ground, with the upper part being lined with casing. The casing prevents the collapse of the borehole walls and (with a drive shoe or grout seal) prevents surface or subsurface contaminants from entering the water supply. The casing also provides a housing for a pumping mechanism and for the pipe that moves water from the pump to the surface.
The quality of materials used in well construction is an important factor. Casing must meet certain specifications, since substandard pipe does not have sufficient strength to withstand driving without potential damage to the joints. Such damage may allow shallow or surface water to enter the well.
The casing must also have a drive shoe attached to the bottom to prevent damage during driving and to make a good seal with the formation. In some applications, a grout seal of cement or bentonite may also be recommended to prevent contamination.
Below the casing, the lower portion of the borehole is the intake through which water enters the well. The intake may be an open hole in solid bedrock or it may be screened and gravel-packed, depending upon the geologic conditions.
Once the well is completed, it is bailed or pumped to develop the well and determine the yield. Many areas need further work after drilling to remove fine material remaining from the drilling process so that water can more readily enter the well. Possible development methods include compressed air (blowing), bailing, jetting, surging, or pumping. The quantity of water (yield test) is usually measured during development. The minimum test time is one hour.
After proper disinfection, the well is capped to provide sanitary protection until it is hooked into the customer’s system. Well caps require an air vent. The purpose of the vent is to equalize the air pressure between the inside of the casing and the atmosphere, and to release unpleasant or explosive lighter than air gases. If such gases are present and the well is enclosed in a building or confined space, the air vent should always be extended to the outside atmosphere. The vent pipe must be shielded and screened to prevent the entry of foreign material such as insects into the well.
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The cap covering a well may be a small part of the overall household water well system, but it is an extremely important one.
A properly installed well cap separates potential pollutants from your drinking water. The cap, which should be sealed tightly at all times, keeps out everything from liquid contaminants to bugs that can crawl inside a well and wreak havoc.
Following is more information about the well cap, a small device that can make a big difference in the water quality of your household water well system.
What is a well cap and what does it do?
The well cap is the cover on top of the well casing that sticks out of the ground. It serves many purposes. Most caps, which are usually aluminum or a thermoplastic, include a vented screen so that the pressure difference between the inside and outside of the well casing may be equalized when water is pumped from the well. However, the cap's main function is to keep contaminants out of the water supply.
What type of contaminants does the well cap keep out of the well?
A properly sealed well cap protects against all types of contamination. It is the first line of protection against nonpoint source pollution, which constitutes the majority of ground water contamination. Nonpoint source pollution includes runoff of pesticides and herbicides, soil erosion, and elements from the street.
Well caps also keep out insects, such as earwigs, which prefer a dark, damp environment to nest. Insects can cause major problems in a well. Bacteria levels can rise from their droppings, and sometimes the bugs themselves can get trapped in the wells, die, and decompose in the well water.
Does the well cap make my water safe?
Surface water can encounter many types of pollutants and transport them. These are not always easily detected by taste or smell. A properly sealed well cap is a safeguard in preventing those contaminants from penetrating the household water supply.
Having your well tested is the surest way to determine that the water is safe. Even if your well cap fits tightly on your well and your water tastes fine, the water well system should be given a checkup by a contractor every year.
Is there anything else I can do to ensure the water is safe?
Check the well cap from time to time. Make sure that it is sealed tightly, and look for cracks and evidence of tampering. If your well cap has a lock, check to see if the lock has been tampered with. Also, practice safe water habits. Do not landscape around the well cap. If you landscape your yard, make sure there is not a low area near the well where rain water could collect. Rain water can carry pollutants that can seep into a well. And when working with oil and gasoline, or mixing herbicides or pesticides, do so over concrete so spills can't seep into the ground.
Is it OK to cover the well cap?
If you don't like the look of the exposed casing and well cap sticking out of the lawn you can camouflage it. There are companies that manufacture plastic covers designed to look like landscaping boulders. Often called "mock rocks," the products are lightweight, hollow, and durable to the elements. The covers, which come in a variety of sizes and shapes and are growing in popularity, have been used to cover everything from well heads to septic access ports and risers, tanks, utility panels, and water garden devices.
If drilling produces poor quality water, the water can be sealed off. One method is to install additional casing or liner inside the original casing and grout it into place. If the water quality remains unsatisfactory, or if construction defects cannot be remedied, the well must be abandoned and completely sealed to prevent cross-contamination between sites.
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Casing is the tubular structure that is placed in the drilled well to maintain the well opening. Along with grout, the casing also confines the ground water to its zone underground and prevents contaminants from mixing with the water. Some states or local governing agencies have laws that require minimum lengths for casing.
The most common materials for well casing are carbon steel, plastic (most commonly, but not exclusively, PVC), and stainless steel. Different geologic formations dictate what type of casing can be used. For example, parts of the country where hard rock lies underground are known strictly as "steel states."
Residents in some areas have a choice between steel and PVC, both of which have advantages. PVC is lightweight, resistant to corrosion, and relatively easy for contractors to install. However, it is not as strong and not as resistant to heat as steel. Steel, though, is susceptible to corrosion, can have scale build-up, and can cost more than PVC.
Some contractors also use concrete, fiberglass, and asbestos cement casing.
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Well screens are filtering devices used to prevent excess sediment from entering the well. They attach to the bottom of the casing, allowing water to move through the well, while keeping out most gravel and sand. The most popular screens are continuous slot, slotted pipe, and perforated pipe.
Perforated pipe is a length of casing that has holes or slots drilled into the pipe. It is not efficient for aquifers that feature a lot of sand and gravel because it has wide openings.
There is less open area in the other two types of screens. Continuous slot screens are made of wire or plastic wrapped around a series of vertical rods. Slotted pipe screens, which have the least amount of open area, feature machine-cut slots into steel or plastic casing at set distances.
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Pitless adapters provide wells with a sanitary -- and frost-proof -- seal between the well casing and the water line running to the well system owner's house.
After a frost line is determined for the area where the well is being installed, the adapter is connected to the well casing below the frost line. Water from the well is then diverted horizontally at the adapter to prevent it from freezing.Planning for a Water Well
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Before you build your house or drill your well, plan your water supply. A house is worth little without an adequate supply of good quality water, which may be found where you had hoped to build the front steps!
First, check to see if your local government requires a well permit prior to drilling a well. Or, talk with your contractor about legal requirements to insure that the proper permits, if any, are obtained.
When drilling a well, you are exploring to determine the quantity and quality of water available. Totally dry holes are uncommon, but low-yielding wells are more so. Some causes of low yield include a low natural or seasonal water table, interference with other wells (for example, in a subdivision), and geologic conditions.
If problems arise, the cost to repair them is less if you construct the well first, because only the cost of the well is involved. Also, if a second well must be drilled, there is more likely sufficient space on the property if the house is not already there. If you are thinking about purchasing a property in an area where adequate water supply is questioned by your licensed and certified driller, then an option on the property is better, with permission to have a well constructed first.
The type of material beneath the ground surface in your area can tell you how successful you may be in obtaining a suitable water supply from a well. Your local drilling contractor will have experience in the area and should be able to tell you what to expect. Also, neighbors in the area should be able to tell you about quantity and quality.
Everyday use: drinking, cooking, and water for "plumbing" (toilets, bathtubs, showers, automatic washers, dishwashers, and many other water using automatic appliances)
Seasonal use: lawn and garden watering, car washing, and swimming pool
Other special uses: animal watering, crop irrigation, and water treatment devices that require backwashing
Fire protection: this is a special need for which a home seldom depends on a well. The local fire department usually has access to large quantities of water from non-drinkable ponds or surface water.
A day’s use may be concentrated into a period of one to two hours, often in different areas of the house at the same time (laundry, bathroom, and lawn). The water supply system must be able to meet this type of peak demand. A conservative estimate is that a home will need about 150-300 gallons per day for two to four people to meet all these needs.
Three factors must be considered when determining how much is enough:
Flow Rate: continuous rate of tield for well
Size of the well: diameter and depth of well
Static Level: level at which water stands in a well when no water is being pumped from the well.
In addition to providing for regular household use, wells sometimes supply water for heating and cooling purposes. Some energy-conscious homeowners install ground water geothermal systems, which extract and concentrate heat energy from water and make it available for heating or cooling purposes. Ground water below 20 feet from the surface remains at a constant temperature. The temperature of well water is equal to the average air temperature of the area.
The actual location of your well will often be determined by factors other than geology. Land surface features such as steep slopes and poorly drained areas are considerations in the location of the well and building. Whenever possible, wells should be located at higher elevations than the surrounding areas to decrease the potential for contamination.
The well should be located and maintained so that it is accessible for cleaning, treatment, repair, testing, inspection, and other activities which may be necessary over time.
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The most common problem associated with ground water may be hardness, generally associated with an abundance of calcium and/or magnesium dissolved in the water. Hard water has not been shown to cause health problems, but can be a nuisance as it may cause soap curds and deposits to form on pipes and other plumbing fixtures. Over time this can reduce the diameter of the pipes.
Calcium and magnesium are found in ground water that has come in contact with certain rocks and minerals, especially limestone and gypsum. When these materials are dissolved, they release calcium and magnesium. Hard water is considered bad for your plumbing, but people with heart or circulatory problems may want to consult their physician about drinking softened water, because the softening process removes calcium and magnesium, and adds sodium to the water.
Iron and Manganese
A "rusty" or metallic taste in water is a result of iron, and sometimes manganese, in ground water. They not only create a bad taste, but they also can stain pipes and clothing.
Iron and manganese are naturally occurring, and most ground water has some amount of dissolved iron and manganese in it. It comes from contact with minerals that contain iron, such as pyrite.
There are several treatment methods. Installing a water softener may help if iron and manganese are present in low quantities and the softener is designed for their removal. Aeration (the addition of oxygen to the water), chlorination, and feeding ozone or hydrogen peroxide can aid in the precipitation of iron, which it is removed from the water by filtration. Potassium permanganate feed with manganese greensand filters, and some recently designed synthetic media, will remove iron and manganese, as well.
Most nitrogen in ground water comes from the atmosphere. Some plants can "attach" nitrogen from the atmosphere onto their roots. The nitrogen not used by the plants is then released into the soil.
Nitrogen compounds also can work their way into ground water through fertilizers, manure, and urine from farm animals, sewage, and landfills.
The most common forms in ground water are ammonia, nitrate, and nitrite. Nitrates can be especially toxic to children under six months of age. Exposure to ammonia also presents a health risk. It is toxic to aquatic life such as fish, and it interferes with water treatment.
There are a variety of treatment methods to correct this problem, including reverse osmosis systems with water softeners to remove nitrates and nitrites, and oxidation to remove small amounts of ammonia. However, treatment should be a last resort. Removing the source of contamination is the first priority. You should also be sure to protect the area around the wellhead from contamination by animals or fertilizers.
Silica comes from the weathering of silicate minerals in the ground. It causes no harmful effects to humans, but large amounts can cause scaling in pipes that impacts water flow, and it can interfere with iron and manganese removal.
Sulfur can occur in ground water in two forms: sulfides and sulfates. Sulfides are naturally occurring in much of the United States in limestone containing organic materials; ground water affected by oil, gas, and coal deposits; in marshes and manure pits; and in the byproduct of well-established iron biofilms. Sulfates often come from the dissolving of minerals, such as gypsum and anhydrite.
A “rotten egg” smell coming from your water indicates the presence of hydrogen sulfide gas. Along with creating an unpleasant odor and taste, sulfides cause corrosion to plumbing and darken water.
There are several methods for treating sulfur. Aeration, ozone, hydrogen peroxide, and chlorine (best followed by filtration) are effective against dissolved hydrogen sulfide or gas. A reverse osmosis system, nanofiltration system, or a negative ion-exchanger also can be effective in reducing sulfates. Filtration is necessary in combating sulfur formation as a mineral or in biofilms.
Total Dissolved Solids
TDS, as it is commonly known, is the concentration of all dissolved minerals in water. It is the direct measurement of the interaction between minerals and ground water.
TDS levels above 1000 mg/L will usually yield poor tasting water. Levels above 2000 mg/L are considered undrinkable due to taste, and levels more than 10,000 mg/L are defined as undrinkable.
Water softeners with a reverse osmosis system are effective in lowering the TDS to satisfactory levels.
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