Water Table.
—The upper level of the saturated portion of the soil is known as the water table. It has a definite surface that conforms to the broader surface irregularities. While a definite, determinable water table appears only in porous soil, it exists even in dense rocks. It rises and falls in wet seasons and in drought. In exceptionally wet seasons the water table may be at or above the surface. Under such conditions the opportunities for the pollution of wells is much increased. In particularly dry seasons the water table may sink below the bottom of the well, when it is said to “go dry.” The water table follows the surface contour in a manner depending on the character of the soil. It is flattest in sand or gravel areas but in clay it follows the contour of deep slopes with but slight variation.
The Devining Rod.
—The use of the devining rod, for the purpose of locating suitable sites for wells, has been supposed by many to be a gift possessed by a chosen few. The devining rod is a forked branch of witch hazel, peach or other wood, which when held in the hands and carried over the ground, is supposed to indicate the presence of water by bending toward it.
In most cases the operators are entirely honest in their belief and in a large proportion of trial their efforts have been successful in locating desirable wells; but it has many times been proven that the movement of the rod is due to an unconscious muscular movement of the arms and hands, in places where the operator has previously suspected the presence of water. The operator of the devining rods is most successful in regions where water occurs in sheets, such as often occur in gravel or pebbly clay. The successful use of the devining rod cannot be explained by any scientific reasons. There have been invented a number of devining rods, claimed by their inventors to be based on scientific laws; but the government has not yet granted patents to appliances of the kind.
Selection of a Type of Well.
—The chief factor which controls the selection of a type of well is the nature of the water-bearing earth, the amount of water required, the cost of construction and the care of the resulting supply.
If a large amount of water is to be demanded of a well, to be dug in soil through which the water percolates slowly, the well must be large in diameter, in order that the necessary supply may be accumulated. If the earth is porous and yields its water readily, a small iron pipe driven into the ground may supply the desired amount.
The character of the water-bearing material is of the greatest importance in determining the yield of the well. In quicksand, water is usually present in ample quantities, yet owing to the extremely fine particles of which the quicksand is composed, its presence as a water-bearing soil is highly undesirable.