Part 7 (1/2)
If the well is a driven well and the water in the casing falls so low that the ordinary suction pump will no longer draw, two remedies may be applied. A so-called deep-well pump may be used; that is, a pump which fits inside the piping and can be lowered down to the water level. The ability to bring up water then depends on the power to work the pump and on the presence of the water. Figure 22 shows the principle on which this pump works. At some point, it may be three or four hundred feet below the surface of the ground, a valve _A_ opening upward is set in the well so that it is always submerged. Just above this is a second valve fastened to the lower end of the long pump rod which reaches up to the engine or windmill which operates the pump. At each up stroke water is lifted by the closed valve _B_ and sucked through the open valve _A_.
At each down stroke, the water is held by the closed valve _A_ and forced up through the open valve _B_.
[Ill.u.s.tration: FIG. 23.--Pump installation.]
The other method of developing a greater quant.i.ty of water from a deep well is to use air pressure to force the water either the entire distance to the tank or to a point where the suction of an ordinary pump can reach it, as indicated in Fig. 23. In this method an air blower is needed, and since this means an engine for operation, it is not generally feasible, but is suited to occasional needs, where an engine is already installed for other purposes and is therefore available.
The operation is very simple. An air pipe leads from a blower and delivers compressed air at the end of the air pipe, which must be below the level of the water in the well. The pressure of the air then causes the water to rise, the distance depending on the pressure at which the air is delivered.
CHAPTER VI
_SOURCES OF WATER-SUPPLY_
Having arrived at the quant.i.ty of water necessary to supply the needs of the average household, we must next investigate the possible sources from which this quant.i.ty can be obtained. Before the advantages of running water in the house are understood, a well is the normal and usual method of securing water, although in a few cases progressive farmers have made use of spring water from the hillsides. It is rare, indeed, for surface water, so called, to be used for purposes of water-supply until after modern plumbing conveniences have been installed. Then the use of surface water becomes almost a necessity because of the large volume of water needed. The only drawback to its use is its questionable quality. Without modern plumbing, a well meets the requirements of family life, but does not answer the demands of convenience. With modern plumbing, a well is found to be pumped dry long before the domestic demands are satisfied. The result is an attempt to secure an unfailing supply, and for this a surface supply is sought.
Let us divide, then, the possible sources of water for domestic consumption into two groups, those found under the surface of the soil and those found on or above the surface. In the first group will come wells and springs, and in the second group will come brooks, streams, and lakes.
_Underground waters._
Springs result from a bursting out of underground waters from the confined s.p.a.ce in which they have been stored or through which they have been running. Thus in Fig. 24 is seen how water falling on the pervious area _a-b_ is received into the soil and gradually finds its way downward between impervious strata which may be clay or dense rock. At the point _B_, where the cover layer has, for any reason, been weakened, the pressure of the water forces its way upward and a spring is developed at the point _C_. Or, conditions may be as shown in Fig. 25, where the confined water, instead of being forced upward by pressure, flows slowly out from the side of a hill, making a spring at the point _D_, while the water enters the pervious stratum at the point _a-b_ as before.
[Ill.u.s.tration: FIG. 24.--Diagram of a spring.]
[Ill.u.s.tration: FIG. 25.--Water finding its way from a hillside.]
[Ill.u.s.tration: FIG. 26.--The sinking of wells.]
If the water is held in the ground as in the first case, it is possible to develop the spring artificially; that is, to drill through or bore through the overlying impervious strata so as to allow the escape of the water. When this happens, the water bursts forth exactly as in a natural spring except that under some conditions the pressure may be sufficient to force the water rising in a pipe instead of through the ground to flow above the surface of the ground as a fountain or jet, making what is known as an ”artesian well.” A true well, on the other hand, may be put down in the ground and through strata where springs could never develop; that is, where no pressure exists in such a way as to bring the water to the surface, as in Fig. 26. The well here is sunk until it reaches the water, and it is safe to say that one can always reach a layer of water in the ground by a well if the well is deep enough.
The flow of underground water is, however, always very uncertain and confusing, and even in localities where water would naturally be expected in quant.i.ty, as, for instance, in the bottom of a valley filled with glacial drift, much disappointment is often experienced because the expected water is not found. The city supply of Ithaca, New York, is a case in point. For six miles south of the lake there is a broad, almost level valley filled many hundred feet deep with glacial drift and presumably filled with water flowing at some unknown depth below the surface into the lake. When the city was recovering from the typhoid fever epidemic which, in 1903, committed such ravages, well water seemed to the panic-stricken citizens the only safe water. Geologists were called in, and they gravely a.s.serted that the valley contained glacial drift to a great depth and that an ample supply of pure water could be counted on. It was known that water was met all through this valley at depths of from six to twelve feet and then that there would be found a layer of finely powdered silt to a depth of about one hundred feet, when another layer of water would be found, and that all the private wells reached this layer. When tested by the city, however, it was found that this water-bearing stratum was of too fine material to yield its water freely, and the supply from the depth was altogether inadequate. In one section of the town large quant.i.ties of good water were found at a depth of about three hundred feet, and the city thought that other wells of the same depth should add to the quant.i.ty, but experiment showed that this three hundred-foot water was limited to one particular section, and after a considerable expenditure of money, an underground water-supply for the city was given up.
_Ordinary dug well._
The ordinary well at a farmhouse is what is known as a shallow well or sometimes a ”dug well,” usually ten to twenty feet deep. This type does not usually pierce any impervious layer and thus reach a water-bearing stratum, otherwise inaccessible. The water is found almost at the surface, and the depth of the well is only that necessary to reach the first water layer. A very good example of this kind of well is to be found on the south sh.o.r.es of Long Island Sound, where a pipe can be driven into the sand at any point, and at a depth of a few feet an abundant and cheap supply of water may be secured. The amount of water that such a well can furnish depends upon the area from which the water comes and upon the size of the particles of sand or gravel through which the water has to percolate, it being evident that the finer the material, the more difficult for the water to penetrate.
The writer remembers superintending the digging of trenches in the streets of a city where the texture of the soil varied continually from clay to sand and even to gravel, all saturated with subsoil water into which wells could have been dug. It was very striking to see how the coa.r.s.eness of the material affected the quant.i.ty of water that had to be pumped from the trenches,--the finest sand requiring only one hand pump at a time, while the coa.r.s.e gravel required either a dozen men or a steam pump to keep a short trench reasonably free from water. The same conditions exist when a well is in operation, modified by the fact that the coa.r.s.e material yielding a larger supply will be most quickly exhausted unless the area drained is very large.
A shallow well is most uncertain as to its quant.i.ty and is likely to be of doubtful quality. There are, however, some examples of shallow well supplies which furnish large amounts of water; as, for instance, the one at Waltham, Ma.s.sachusetts, or at Bath, New York,--the latter, a dug well some twenty feet in diameter and about twenty-eight feet deep, furnis.h.i.+ng a constant supply of good water to a village of about 4000 people.
_Construction of dug wells._
The construction of shallow wells requires little comment. Ordinarily, they are dug down to the water, or to such a depth below the level of the water as is convenient, by the use of an ordinary boat pump to keep down the water, and then are stoned up with a dry wall. Such a well for a single house requires an excavation of about eight feet diameter, with an inside dimension of about five feet.
[Ill.u.s.tration: FIG. 27.--Mode of sinking a well.]
If the soil at the bottom of the well is sandy, it is possible to take a barrel or a large sewer pipe and sink it into the bottom of the well in the water by taking out material from the inside and loading the outside to keep it pressed down into the sand. This same plan may be used to sink the whole body of the well wall, first supporting the lower course of masonry on a curb, so called (see Fig. 27). This curb is usually made of several thicknesses of two-inch plank well nailed together, the plank breaking joints in the three or four layers used. It is a good plan to have this shoe or curb extend outwardly beyond the walls of the well so that some clearance may be had, otherwise the dirt may press against the walls so hard as to hold it up and prevent its sinking. While this arrangement may be put down in water, it requires some sort of bucket which will dig automatically under water and has not been therefore a customary method except for large excavations where machinery can be installed. There is no reason, however, why the method might not be used for a single house.
[Ill.u.s.tration: FIG. 28.--A well that will catch surface waste.]
In whatever way the well is dug, one point in the construction that needs to be emphasized is that the wall should be well cemented together, beginning about six feet below the surface and reaching up to a point at least one foot above the surface. This is to prevent pollution from the surface gaining direct access to the well, and if this cementing is well done for the distance named, it is not likely that any surface pollution in the vicinity of the well could ever damage the water. Figure 28 shows the section of a well where no such precautions have been taken, and it is evident that not only surface wash, but subsurface pollution may readily contaminate the water. Figure 29 (after Imbeaux), on the other hand, shows a shallow well properly protected by a good wall and water-tight cover. Figure 30 shows a photograph also of this latter type of well. Even if a cesspool or privy is located dangerously near the well, in the second case the fact that the contaminating influence must pa.s.s downward through at least six feet of soil before it can enter the well is a guarantee that the danger is reduced to the smallest possible terms.