 |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
There is water at some depth almost everywhere beneath the earth's surface. A well is a dug or drilled hole that extends deep enough into the ground to reach water. Wells are usually circular and walled with stone, concrete or pipe to prevent the hole from caving in. They are sunk by digging or drilling through one or more layers of soil and rock to reach a layer that is at least partially full of water called an aquifer. The top of the aquifer, or the level beneath which the ground is saturated with water, is called the water table. In same areas there is more than one aquifer beneath the water table. Deep wells, such as those sunk by large motorized equipment, can reach and pull water from more than one aquifer at the same time. However, this manual will only discuss sinking wells to the first usable aquifer with hand-powered equipment.
A new properly built well can provide people with more and better water. But the new well itself may have little or no impact on the surrounding community's health if the well users do not know how to make effective use of the water.
It is important to learn the water needs of a local population in order to construct an appropriate water source. In all locales an adequate supply of clean water is essential for maintaining and improving health. Many of the most common and serious diseases in developing countries are closely related to the amount and quality of water people use. Without an adequate supply of clean water, little can be done to control diseases that spread through contaminated water supplies.
In order to ascertain local needs, you must consider two limiting aspects to the provision of water: 1) the quality of the water and 2) the quantity of water available locally.
Good quality water does not contain chemicals and bacteria which are hazards to health and life. The quality of water can be assured by:
· locating the site to avoid possible water contamination;· proper construction of the well or any other water source, to protect the water supply from contamination;
· initial and periodic water treatment, usually with chlorine, to kill dangerous bacteria (see Appendix VIII, Water Treatment);
· education of the local users so that they can maintain the purity, or at least prevent the gross contamination of their water.
The quantity of water is often more difficult to ensure. Especially in a rural setting, access (distance) to water will often limit the amount that can be used by each individual, because of the time needed to convey it. Quantity, however, has a direct bearing on health.
Five liters per person per day is considered the minimum consumption level, although desert dwellers exist on less. More than 50 liters per person per day, it has been estimated, gains no further health benefits. Twentyfive liters per person per day may become an acceptable goal in places where piped connections to individual houses are not feasible. Wherever possible, water use beyond minimum-level consumption should be encouraged. Consumption will rise under the following circumstances:
· new well construction to provide a water source closer to a group of people, who will then presumably be able to gather more water in the same amount of time that they previously were able to do;· education of local users toward a greater use of water, especially for hygienic purposes (bathing, washing clothes and cooking utensils).
The quantity of water needed may also be significantly affected by the number of livestock that require water and by whether the water is to be used for garden irrigation.
The degree of community participation and control may be the most important factors in determining the success of any wells construction project. The ideal situation is that the entire project be completely controlled and run by the local people. This, however, is often not possible. It therefore becomes the task of the development worker to see that a community in need of a better water supply is encouraged to realize that need and act to meet it.
It is usually best to use the decision-making systems that have already been established and accepted by the community. These systems vary between open town meeting-type forums where everyone who wishes to can speak, and a relatively closed council or other politically established group or person. In all cases, each of the various possibilities for well construction should be fairly presented so that whatever decisions are made realistically reflect the needs and concerns of the decision-making unit.
Some kind of organized educational campaign should be an integral part of every water supply improvement project. The benefits to be gained from using larger quantities of clean water are not often understood by the local users. Unless they can be convinced of the benefits clean water can bring to them and their children, they are not likely to make effective use of a newly developed water source. In societies where change is often very slow, such an attitude change will take time. Only when the people become willing to act on their understanding of the importance of clean water and what needs to be done to keep it clean can any water supply improvement project be truly successful.
This educational effort is probably one of the most important and difficult aspects of water supply development. Even with a massive education campaign, real I change may take many years. But without it, a supply of clean water may mean nothing.
Such a campaign of education is especially important for the future maintenance of the well. If people can see clean water as being vital to them, they will be willing to occasionally spend a little time or money to keep their water supply safe. However, where people are not involved in planning and, to some extent, construction from the beginning,no amount of general education later will be effective.
When the community has decided that more and better water is needed, it will be necessary for them to decide what kind of source is possible and will best suit their needs. A well is not always the most appropriate water source in a particular locale. Their goal is to find the cheapest, most reliable way to provide the needed amount of clean water.
Here are the chief potential sources of water listed in their approximate order of preference based on cost, quality of water, need for equipment and supplies:
· Springs - If there are year-round springs nearby, they can usually be developed to supply clean water. This water can often be conveyed through pipes without the expense of pumps or water treatment. Springs can most often be found in hilly or mountainous regions (see Fig. 1-1):· Wells - Because there is water at some depth almost everywhere beneath the earth's surface, a well can be sunk (using the appropriate technique), almost anywhere. The water that comes into the bottom of a well has filtered down from the surface and is, in most cases, cleaner than water that is exposed on the open ground;
· Rainwater - Collection and storage of rainwater may provide another source where surface and underground water supplies are limited or difficult to reach. Normally, except in the rainiest regions, rainwater will not supply all the water needs of a locale; however, as a supplement, it can be collected from roofs or protected ground run-off areas, and stored in covered cisterns to prevent contamination.
FIG. 1-1. SPRING LOCATION
· Surface water - Streams, rivers, and lakes are all commonly used as sources of water. Although no construction is needed to enable them to supply water, the quality of the water is almost always poor. Only clear mountain streams flowing from protected watersheds could be considered as fit for human consumption.
Locating the site for a well should be based on the following guidelines:
The well should be located at a site that is:
· water bearing;
· acceptable to the local community;
· suitable to the sinking methods available;
· not likely to be easily contaminated.
It is not always possible for a site to meet all of these guidelines. Therefore, a site will need to be chosen which best approximates the guidelines, with particular emphasis on the likelihood of reaching water (see Fig. 12). Where there is an equal chance of reaching water at several different locations, the one closest to the users is preferable.
· Where is water likely to be found?
A development worker can assist the community's effort to locate a likely site by collecting available information on local ground water. In many countries, some information is available through appropriate ministries, water agencies, and international development organizations.
Choosing the site for a well can be difficult, because easily available and abundant water can never be guaranteed. Even professionals, before a well is sunk, rarely know where they will reach water and how much will be available. However, there are a number of guidelines which can be very useful in providing information about possibly successful well sites.
Where possible, a well can be located near a past or present water source. By doing so, you are likely to reach water at approximately the same depth as the other source.
If no other sources exist or have ever been developed nearby, you must be more cautious in choosing a well site. Unless you have the benefit of detailed geological information, it is best simply to look for the lowest spot nearby. Both surface and ground water are likely to collect here. In some cases, plants can be indicators of the presence of ground water (see Appendix, Vegetation as an Indicator of Ground Water). However, be careful not to build in a place so low that the well would be susceptible to flooding in heavy rain.
FIG. 1-2. POSSIBLE WELL SITES
1) Limited water would be available at this site, because the impermeable rock layer is close to the ground surface, allowing slight fluctuations in the water table to drastically affect water availability.2) Closest site to village and therefore the best site if it is possible to dig down far enough to reach water.
3) At this site, there would be a better chance of reaching more water that at 2. but the site is further from the village.
4) This is the site where water is most likely to reached by a well although it is some distance from the village. Because it is in the absolute bottom of the valley, it may be subject to flooding.
· Is the site acceptable to the local community?
The community must accept the final site choice and be willing to use the well when it is completed. Only then will it benefit local residents.
· Is the site suitable to the available sinking methods?
If the most likely site would require that the well penetrate a layer of rock, and if there are no tools available to do so difficult a job, the site is not an appropriate one.
· Is the well likely to be easily contaminated?
The most important consideration here is that the well not be located within 15 meters of a latrine or other sewage source. This would also include not placing the well where it might be damaged or inundated by a flood or heavy rain.
What is the optimum well design for the prevention of contamination?
The only way to design a well to prevent water contamination is to seal it so that water can enter only through the bottom section. Dug wells need to be covered with a permanent cover through which a pump is installed to draw water. All wells should have a platform around them that is at least 1 meter wide, one which water will not penetrate. This platform ought to be sloped in such a way that any spilled water runs off away from the well. (See Figs. A and B on inside of front and back manual covers.)
These and other measures are described in more detail in the design section for the different types of wells (pp. 23 and 124).
In general, there are two types of wells: dug wells and drilled wells. The obvious difference between the two is the size of the holes. (See Figs. A and B).
Dug wells are sunk by people working down in the hole to loosen and remove the soil. They need to be at least 1 meter wide to give people room to work.
Drilled wells, on the other hand, are sunk by using special tools which are lowered into the ground and worked from the surface. These wells are normally less than 30 centimeters (cm) in diameter, and for the purpose of this manual, will usually be less than 15 cm. The reason for this is the difficulty of drilling larger holes with hand-powered tools.
In both categories, there are many different specific sinking techniques which will be discussed in more detail later.
Every well, whether drilled or dug, has three sections: top, middle, and bottom. Each of these sections varies in construction, because each must function differently. (See Figs. A and B.)
· Top section - That part of the well at or above the ground surface level. It should be designed to allow people to get water as easily as possible, and, at the same time, to prevent water, dirt, and other contaminants from entering.· Middle section - That part of the well which is between the ground surface and the water, This section is usually a circular hole. It is reinforced with some kind of lining to prevent the walls from caving in.
NOTE: Lining and casing refer to the same part of the well (see Figs. A and B). Lining is used to refer to that part of the dug well, while casing refers to the pipe used to reinforce a drilled well.
· Bottom section - That part of the well that extends beneath the water table into the aquifer. It should be designed to allow as much water as possible to enter, and yet prevent the entrance of any soil from the aquifer. Its lining will have holes, slots, or open spaces, allowing water to pass through.
1. Availability of Materials
Even as you are beginning site selection and community awareness activities, you should determine the availability of construction materials and the difficulty in obtaining them. Later you will need to assess in greater detail the specific tools and supplies needed, and the quantities of each.
First of all, can you get cement or pipe? If cement is available, it should be fresh and powdery, and not congealed in hard clumps. Cement, sand, gravel, and water can be mixed to make concrete which when it hardens is very strong and long lasting especially when reinforced with steel reinforcing rod (rerod). If neither cement nor pipe is available, you will need to find a local material that can serve as the lining. (See p. 38.)
Metal, plastic, or concrete pipe can be used. Metal pipe, usually galvanized iron or steel, is more durable for well sinking but is subject to corrosion and rusting over time. Plastic pipe, on the other hand, has less strength and is not easy to use in the sinking process. Nevertheless, it is virtually unaffected by ground water quality. Large diameter concrete pipe can be used to line dug wells.
If you can get these basic materials, you will probably be able to find the other related tools, equipment, or adapt local equipment. A local metal worker (welder or blacksmith) can probably make any special tools you may need. For a list of these, see page 37 of the next section.
2. Use of Local Materials
Construction of a well is cheaper, more easily understood, and more likely to be incorporated into the culture if the builders use local materials whenever possible.
The materials required to construct the bottom section, lining, well head, and pump (see Figs. A and B) should be sufficiently strong to withstand the stress of installation and the wear and tear of daily use. They should also be able to support the weight of the column where necessary and not contaminate the water, as a result of natural wear, during the lifespan of the well.
In emergency situations, when the best water available is immediately needed, a number of substitute materials and techniques can be used. For example, wood lining can be used instead of cement. Wells built with wood or other substitute materials and techniques will supply acceptable water for a short period of time. However, they cannot now or in the future be converted into permanent sources of clean water without rebuilding major portions of the structure.
3. Materials for Well Parts
The two most important sections of the well are the lining (or casing), and the bottom (or intake) section. While it is not necessary that both be built of the same material, it is often cheaper and more convenient to do so. Almost all modern well linings are made of either concrete or pipe (metal or plastic).
Nowadays, concrete is used most often in the lining of hand-dug wells. It can be easily mixed and cast in place in the well. Reinforcing bars can be added to either mortar or concrete to make a much stronger and more durable lining. (See Appendix IV, Concrete.)
Metal pipe is normally used in the construction of drilled wells. It can easily be shaped to make the necessary tools with which to sink the well and can also serve as the permanent casing and bottom section.
Plastic pipe is too soft to use during drilling but is in many situations a better casing than metal pipe, because it will not rust or corrode.
Cement and pipe are available in most countries and usually in all but the most remote regions. When both materials are available, consider such factors as transportation, type of well, depth, ease of construction, and adaptability to local practices before deciding which is the more appropriate.
The choice of tools and equipment will depend on the construction material and its use. Many basic tools can be used to perform a number of different functions. However, a job is more easily and quickly done with the tool designed for that job. The following are the tools and equipment recommended for wells construction: hammer, nails, wood, saw, hacksaw, chisel, mason's trowel, level, shovel, mixing hoe, pick, ruler, plumb-bob, buckets, heavy rope, pulley, square, pliers, crow-bar, wrenches, pipe wrenches, screwdriver, file, mason's hammer, tie wire, sheet metal, pipe cutter, tripod, and pipe threader. For specifics, see the chapters on sinking methods in the sections on Dug Wells (Chapters 7-8) and Drilled Wells (Chapters 12-14).
A sinking method is a specific way of sinking a well. Wells may be dug by hand, drilled with hand tools, or drilled with motorized equipment. Many methods and techniques are used. The particular choice depends on the available materials and equipment, the expected ground conditions at the well site, and your familiarity with a specific sinking technique.
Motorized drilling techniques are summarized in the section on Drilled Wells, but are not described in detail because of the high level of technical expertise necessary in the use of the equipment.
The following are general descriptions of hand-dug and hand-drilled sinking methods. For more details, see the manual sections on Hand-Duq Wells and Drilled Wells.
1. Hand-dug wells are sunk by digging a hole as deep as is necessary to reach water. Once the water bearing layer is reached, it should be penetrated as far as possible. This process is always basically the same, with only minor variations because of the particular tools and equipment available and the variety of ground conditions (see Fig. 1-3).
Advantages
· This procedure is a very flexible one. It can be easily adapted with a minimum of equipment to a variety of soil conditions, as long as cement is available.· Because the resulting well is wide-mouthed, it is easily adaptable to simple water-lifting techniques, if pumps are not available or appropriate.
· It provides a reservoir which is useful for accumulating water from ground formations which yield water slowly.
FIG. 1-3. DIGGING A WELL
Disadvantages
· A hand-dug well takes longer to construct than a drilled well.· It is usually more expensive than a hand-drilled well.
· It cannot easily be made into a permanent water source without the use of cement.
· Hand-digging cannot easily penetrate hard ground and rock.
· It may be difficult to penetrate deeply enough into the aquifer so that the well will not dry up in the dry season.
2. Drilled wells are sunk by using a special tool, called a bit, which acts to loosen whatever soil or rock is at the bottom of the hole. It is connected to a shaft or line which extends to the ground surface and above. The part of the shaft or line extending above the ground can then be moved to operate the bit (see Fig. 1-4).
FIG. 1-4. DRILLING A WELL
Advantages
· It is fast.· Where cement is not available, wells can be sunk with locally made drilling equipment and lined with local materials.
· While not easy, it is possible to penetrate hard ground and rock formations that would be very difficult to dig through.
· Drilling usually requires fewer people than hand-digging.
· It is especially suitable for use in loose sand with a shallow water table.
Disadvantages
· There are a number of different hand-drilling techniques that are suitable for a wide range of ground conditions. However, each requires special equipment.· Pumps almost always have to be used because buckets are too large to be lowered into the well.
· Limited depth can be reached with hand-powered drilling equipment.
Suitability of Well Construction
Methods to Different Geological
Conditions
Once you have decided how to sink the well and what materials to use, you need to organize and prepare for the construction.
1. Workers
It is best if local laborers perform as much of the work as they are capable of performing without spending too much time in training. This will allow them to better understand the well, its construction, and later maintenance needs.
With any laborers it should be very clearly established before construction begins who is expected to do what, how long is should take, and what quality the end product should be. Any later misunderstandings can be more easily cleared up if an initial understanding was agreed to by all parties.
Consider the following questions concerning the workers:
· What skills are required?
· Will the workers require training?
· If so, how much training?
· How many workers are needed?
· How long will their services be needed?
· Will they volunteer their work or will they be paid?
NOTE: While you can be of assistance, it is important to let the community set their own goals.
2. Materials
Before the construction begins, it is helpful to have at the well site as many of the tools, equipment, and supplies as you think will be necessary to complete the job. This prior organization will facilitate the day-to-day operation. If large quantities of supplies will need to be stored at the site (such as the sand and gravel for concrete) , the storage site should be decided on beforehand so as not to interfere with later work. If theft is a serious problem, workers may have to take turns guarding the construction site at night.
Planning the construction of a well can be complicated. There is the necessity to find the appropriate material, the initial decision as to which sinking method will be used, and the complexity in assessing the ground conditions of the well site. These factors are difficult ones to evaluate, especially when information about local conditions is incomplete. Because situations change, the feasibility studies and planning may have to be repeated and updated before well construction begins.
To help you to plan effectively, the following is an outline of the wells construction process.
Overview of Well Construction
Initial feasibility questions
· Is there a need for water?
· Is a well the most appropriate water source to build?
· Are construction materials available?
· Who can do the work?
Community involvement
· How will the community participate?
· What training is needed?
· How will they be organized?
Technical questions
· Where will the well be sunk?
· How will the well be sunk?
· How will the well be designed to best prevent water contamination?
Construction of the middle section
· Initial site preparation.
· Sinking the hole.
· Lining (casing) the hole.
Construction of the bottom section
· Testing the quality and quantity of water available.
· Sinking and lining below the water table.
· Constructing the bottom plug or filter.
Construction of the top section
· Building the head wall.
· Constructing the platform.
· Installing the pump.
Well disinfection before initial use
Maintenance - The question of who will maintain the well and pump after their construction should be realistically resolved before construction.
After you have read the rest of the manual and have decided how you can best sink a well, you should use this overview as a checklist to make sure that you have considered all the necessary aspects of wells construction.
 |
 |
