Infallible rules cannot be given with regard to the location or depth of a well to assure the finding of a satisfactory water supply either in quantity or quality. Experience with wells in the neighbourhood is the best guide and a knowledge of the local geology and topography is an essential aid.
In general, wells should not be constructed within 50 to 100 ft. of privies or leaching cesspools and locations on hillsides below privies or cesspools should be avoided. The fact that the top of a well is on a hillside above a privy or cesspool is no assurance that the water is safe from contamination. If the bottom of the well is higher than the source of contamination all danger is quite remote.
Three types of wells are in use for private supplies : the dug well, the driven well, and the drilled well. The dug well, as the name indicates, is excavated by means of a shovel.
Such wells are usually circular, 3 or 4 ft. in diameter, and are rarely over 50 ft. deep. Dug wells are classified as shallow wells. They should be lined with masonry blocks or stones laid up without mortar in the joints except near the top of the well. Careful protection should be provided at the top to avoid contamination from surface water and drippings which may fall back into the well.
A driven well is constructed by driving into the ground a pipe, the lower end of which has been drawn to a point, and the sides of which have been perforated for a short distance above this point. A 1 1/4- or a 2-in. galvanized-iron pipe, perforated with 1,500 to 2,000, 1/16- to 1/8-in. diameter holes near the lower pointed end will supply water at the rate of about 5 gal. per minute. Larger pipes with more holes should supply more water but they are more difficult to drive. The diameter of the holes should not be increased but their number can be increased indefinitely.
The pipe is driven into the ground by successive blows of a wooden or protected maul or other instrument which will not flatten the upper end of the pipe. Additional lengths of pipe are coupled on to the lengths already driven in order to reach the desired depth. Such wells are best constructed in sand or other soft porous material. They cannot, ordinarily, be depended upon to supply a large quantity of water. Such wells are seldom driven to depths greater than 30 to 50 ft., and are, therefore, classed as shallow wells.
The drilled well is used for greater depths than can be attained by either the dug or the driven well. -Drilled wells assure water of better sanitary quality and greater quantity than can be expected from shallow wells. The construction of deep, drilled wells requires special well-drilling tools and equipment which are described in books upon the subject.
The diameters of casing used in deep wells vary from 3 to 24 or 36 in. or even larger. A common size of casing for a well to deliver 100 to 200 gal. per minute is around 6 to 12 in. There is no limit to the depth of the well, the rule being to drill until water is encountered. Since the cost of drilling the well increases very rapidly with the depth, the cost of drilling or of pumping finally sets the limit on the depth of the well. The casing is constructed of extra heavy metal designed for the purpose.
The screen, which goes in the bottom of the well, is usually made of brass and is an expensive item in the cost of the well. Well screens must be selected so that the opening in the screen is smaller than the particles of the water-bearing material. The total area of the openings should be sufficient to permit a low velocity of flow into the well at the maximum rate of pumping.
This velocity should not exceed 1 ft. per minute through the screen openings. Screens are sometimes selected with openings slightly larger than the material to be excluded. The finer particles are drawn through the well, leaving the larger particles to pack around the outside of the well forming a larger screen for the infiltration of ground water.
The largest practicable openings should be selected, as small openings tend to corrode and clog more rapidly than large openings. Sometimes the effect of a large screen with large openings is obtained by packing gravel around the outside of a coarse metal screen which is about the size of the well casing.
In placing reciprocating pumping equipment in a well the working barrel is connected to the suction pipe, if one is to be used; a length of sucker rod is attached to the working barrel and a length of “drop pipe” is slipped over this and attached to the working barrel.
The barrel, sucker rod, and drop pipe are then lowered into the well, successive lengths of sucker rod and drop pipe being attached as the working barrel is lowered. The depth to which the barrel should be lowered is the least practicable depth to prevent dewatering of the working barrel during pumping. This depth can be determined only by test. It bears no relation to the depth of the well.
As in dug and driven wells, care should be taken to secure and to maintain a tight joint so as to avoid pollution of the well water.
The development of springs and surface streams calls for a knowledge of the principles, of underground and surface water which, coupled with the exercise of ingenuity and originality, can often be successful in developing an apparently worthless water supply into one of value or in materially increasing the amount of water available from an existing supply.
The source of all underground water is rain water which has soaked into the ground until it has reached the water already in the ground. The surface of the ground water is called the ground-water table. The ground-water table is not level, but in porous ground it follows approximately the contour of the surface of the ground. Only in limestone regions and in fissured rock are large underground streams encountered.
Springs can be divided into four classes for convenience in considering methods for their development:
The first two types of springs are best developed by laying a line of drain tile at right angles to the direction of flow of ground water, and discharging this into a sunken barrel or other sump which will serve as a pump suction pit or source of supply. Springs of the third type can best be developed by the construction of a deep well at the site. Little can be done to increase the flow from the fourth type of spring except to clear away the debris from about the mouth of the spring by pick and shovel or by the use of dynamite.
The development of a surface stream as a source of a private water supply in a populated district is a marked rarity. The quality of the water from a surface stream in an inhabited district is so likely to show pollution as to be unfit for human use without filtration.
For summer camps and remote homes a barrel sunk into the stream near the shore or, if adequately protected against floating objects, out in the stream channel, will serve as a satisfactory intake. Care should be taken when sinking the barrel that the water of the stream will reach it during the lowest stages of the stream.
A well dug in the banks of the stream so that the bottom of the well is about at or slightly below the bottom of the stream should assure water so long as there is flow in the stream. It is to be remembered that the natural direction of flow of underground water is toward a stream and hence a well so located will ordinarily supply ground water of better sanitary quality than the water in the stream.