| Water purification, distribution and sewage disposal for Peace Corps volunteers |
|Section 1: Water supply sources|
Development of a water source includes all work which increases the quantity and improves the quality of the water, or makes it more readily available for treatment and distribution. The development of surface water sources and springs is considered in this section.
In developing a source, dams, floats, galleries, and similar improvements may be used to increase the quantity and quality of the water. Some of the more common improvements are discussed in succeeding paragraphs.
Elaborate developments should be avoided; simplicity brings more rapid results. A temporary water source should not be converted into a permanent one until the area has been reconnoitered for a source requiring less development. All intake hoses or pipes should be equipped with an intake strainer regardless of the clearness of the water source. Suction strainers should be protected from floating debris which may damage, clog, or unnecessarily pollute them. Proper anchorage of suction fires end strainers prevents loss of prime, punctured or kinked lines, and damage to strainer. Figures 11, 12, 13 and 14 depict several of the common methods of suction inlet anchorage.
Water at the intake point should be as clear and deep as possible. The strainer on the suction hose is placed at least 4 inches below the water level. This precaution reduces the possibility of the strainer becoming clogged with floating debris, or the prime being lost due to air getting into the suction line.
SURFACE WATER SUPPLIES
Advantages. For normal field water supply, surface water is the most accessible type of water source. This source also lends itself readily to the purification equipment common to most engineer units. Surface water is the most easily developed source of water. Various methods of constructing intake points for inland surface water sources are discussed below.
Rocks and Stakes. If the stream is not too swift and the water is sufficiently deep, an expedient intake may be prepared by placing the intake strainer on a rock. This will prevent clogging of the strainer by the streambed and provide enough water overhead to prevent the suction of air into the intake pipe, If the water source is a small stream or shallow lake the intake pipe can be secured to a post or pile as shown in Fig. 11.
Pits. When a stream is so shallow that the intake screen is not covered by at least 4 inches of water, a pit should be dug and the screen laid on a rock or board placed at the bottom of the pit. Pits dug in streams with clay or silt bottoms should be lined with gravel to Prevent dirt from entering the purification equipment (Fig. 12 ). The screen is surrounded by gravel which prevents collapse of the sides of the pit and also shields the screen from damage by large floating objects. The gravel also acts as a coarse strainer for the water. A similar method may be provided by enclosing the intake screen in a bucket as shown in Fig. 13.
Dams. The level of the water in small streams can De raised to cover the intake strainer by building a dam as shown in Fig. 14 . In swiftly flowing streams, a wing or baffle dam can be constructed to protect the intake screen without impounding the water (Fig. 15).
Floats. Floats made of logs, lumber, sealed cans, or empty fuel drums can be used to support the intake strainer in deep water. They are especially useful in large streams where the quality of the water varies across its width or where the water is not deep enough near the banks to cover the intake strainer. The intake point can be covered by an adequate depth of water by anchoring or stationing the float at the deep part of the stream. The intake hose should be secured to the top of the float, allowing enough slack for movement of the float. If support lines are used to secure the float to the banks, the position of the float can be altered to correspond to changes in depth by manipulation of the lines. The chief advantage of a float intake is the ease with which the screen can be adjusted vertically. Fig. 16 illustrates two types of improvised floats.
Galleries. Water from muddy streams can be improved in quality by digging intake galleries along the bank. A trench is dug along the bank deep enough so that water from the stream percolates into it so it intercepts ground water flowing toward the stream. The trench is filled with gravel to prevent the sides from collapsing. The intake strainer is placed in the gravel below the water line (Fig. 17 ). The amount of work required to produce the gallery is justified by a reduction in the amount of chemicals needed to coagulate the water, the elimination of the necessity of frequently backwashing the filter and the higher quality of water obtained.
Drive Points. Many times it is advantageous to utilize shallow ground water sources or percolated waters adjacent to a turbid surface water. Well points are issued in 2-inch diameter, 54 inch lengths. A drive cap is driven into the ground with a sledge. Successive sections of pipe, each 5 feet long, are added and driven until the screen is well within the water bearing media. Several well points may be connected in parallel to supply sufficient water to the raw water pump. In developing drive point sources, it must be remembered that the practical limit of suction lift of the pumps issued with field equipment is 22 to 25 feet at sea level. Suction lift pumps can be used, therefore, only where the pumping level in the well will be within the limit of suction lift, or 22 to 25 feet below the position of the pump. At 5,000 feet above sea level, the practical limit of suction lift is only 20 feet. It should be noted the' since a suction-lift pump must create a partial vacuum in the suction line, it is necessary that the line be absolutely airtight if the pump is to function properly.
Springs yielding 20 gallons per minute or more of water can be used as a source of field water supply if properly developed. Springs may be developed by enlarging the outlet of the spring, and by reducing loss by damming and conducting water to storage. To reduce possible pollution, springs should be cleared of all debris, undergrowth, top soil, loose rocks, and sand.
Water which flows from rocks under the force of gravity and collects in depressions can be collected in boxes or basins of wood, tile, or concrete. The collecting box should he large enough to impound most of the flow' and should be placed below the ground level so that only the top is slightly above the surface. The box should be covered tightly to prevent contamination and lessen evaporation. The inlet should be designed to exclude surface drainage and prevent pollution. This requires fencing off the area and providing proper drainage. Fig. shows a spring inlet which has been protected in this manner. The screen on the overflow pipe prevents the entrance of insects and small animals. Another screen on the intake pipe prevents large suspended particles from being ingested by the pump used to distribute the spring water, thereby preventing mechanical failure or reducing it to a minimum.
The flow of water from a spring located on a steep slope of loose earth can he obtained by the following two methods:
1. Constructing deep, narrow ditches leading from the spring to the point of collection.
2. Constructing pipeline tunnels from the spring to the collecting point. Pipe of large diameter is more suitable for this purpose. The water from the tunnels can be trapped by constructing a dam at the point of collection.
Digging is a more positive and more economical method of developing a spring than blasting. In using explosives in developing the yield from springs you should exercise great caution. Blasting in unconsolidated rocks may shift the sand or gravel in such a way as to divert the spring to a different point.
When ground and surface water supplies are inadequate or cannot be used, ground water supplies are developed by constructing wells. Wells are classified into five types, according to their method of construction. These are dug, bored, driven, jetted and drilled wells. Each type of well has its particular advantages, which may be ease of construction, type of equipment required, storage capacity, ease of penetration into certain types of formations, or ease of safeguarding against pollution.