of water that can be poured into the well is an index of the well capacity when pumping; when saturated, the sand yields its contents as freely as it absorbs water. Often the raising or lowering of the pipe a foot or more brings a greater length of the screen into contact with the water-bearing stratum and results in a great increase in yield.

There are two methods of drilling wells, one is the hydraulic rotary and the other is the cable- tool percussion. Drilled wells tend to be the most complicated and require a lot of equipment. In most cases Equipment Operators will be called upon to place drilled wells. The Utilitiesman may be called upon to install pumps and plumbing when the drilling is complete. Development of this type of well will then proceed in a similar manner as any other type of well.

ALTERNATIVE WATER SOURCES

In some regions of the world there is not enough surface or ground water available to support the demands for domestic and fire protection water needs. In these areas it may be necessary to develop alternate sources of water. Rainwater, snow, seawater, water barges, and mobile tanks are a few of the alternate water sources that may be considered.

In tropical regions there is an abundance of rainwater with a rapid rate of surface runoff. The construction of collection surfaces can be a solution to water needs. For temporary or emergency water supplies, collecting surfaces may be constructed by the use of tarps, wooden platforms, metal surfaces, and so on. Usually, however, surfaces constructed for other purposes, such as building roofs, may be used.

More permanent rainwater catchment areas will be cleared, graded, and given an application of cement or other impervious mixture. The catchment area should be located at least 100 feet from any source of subsurface contamination (septic tanks, cesspools, and so on), and as far from other sources of pollution (dust, soot, and so on) as possible. The catchment area and impounding basin should be enclosed by a fence.

Collected waters should be carried by gravity or pumping to closed stowage reservoirs. As rain falls toward the earth, it absorbs dust and such gases as carbon dioxide and oxygen, and, therefore, must be considered unsafe for consumption until treated. Filtration and disinfection are the minimum required treatment.

In some locations water may be so hard to obtain or polluted that it would not be economical to develop any source. In this case, water barges or mobile tanks may be used. Barges or mobile tanks can be filled from ships, tank trucks, or other well points located some distance away. It is important to note that all mobile containers are a temporary water source. Disinfection of their surfaces that will come in contact with potable water is required.

In northern arctic areas where deep wells cannot be sunk through the thick layers of permafrost, and the surface sources are frozen solid, water must be obtained by melting snow or ice. Ice is preferred to snow because it will yield more water for a given volume. Snow or ice may be contaminated. Therefore, all melt produced should be treated before drinking. Approximately 5 cubic feet of snow is required to yield 1 cubic foot of water. In emergencies, personnel can eat small quantities of snow. This snow should be placed in the mouth, rather than being sucked, to prevent chapped or cut lips. Only small quantities of snow should be consumed in this manner because consumption of large quantities will reduce the body temperature.

Seawater is vastly different in its characteristics (as well as in the methods of purification used) from other surface sources. The chemical characteristics of seawater are such that normal coagulation and filtration are ineffective as treatment processes.

In developing seawater sources, consideration must be given to such factors as surf action, saltwater corrosion, suspended sand and silt in the water, living organisms, surface oil along beaches, and the rise and fall of the water level with the tides. If the equipment is located on sheltered bays, harbors, lagoons, or estuaries, it can be supplied by intakes built in the same way as freshwater surface intakes. On small islands where there is insufficient surface and ground water, and on or near open beaches, intakes for equipment can be built as follows:

1. Saltwater wells. Beach wells should, if possible, be used in preference to offshore intakes. Wells can be dug to tap fresh or salty ground water. This eliminates the problems caused by tides, surf, and shallow water close to shore. Such wells have an added advantage in that they can be built back of the shoreline under natural overhead concealment. Driven and jetted wells may also be used effectively at beach locations.