ARTESIAN (fir-te'zhan) WELLS (from the old county of Artois. Lat. Artesia, now part of France. where the oldest well in Europe was bored in 1126). Vertical borings into the ground. to a depth of IOU feet or more for the purpose Of obtaining water from some deeply buried porous stratum, such as sandstone or gravel. in the true artesian well the water should tloW to the surface, but at present the term artesian is applied to any deep well, even where the water is obtained by pumping.
The presence of an artesian water supply in any region depends upon the existence beneath that region of a tilted porous layer, inclosed between two impervious beds. The outcropping edge of the porous bed must, moreover, be of suffi ciently open texture to soak up the rain which falls upon it, and furthermore there must be no escape of the contained water from the lower portions of the bed. It is therefore evident that when such a porous stratum is saturated with water, the latter will be under pressure, the pres sure at any one point amounting to that of a column of water whose height is the difference between the altitude of that point and the alti tude of the outcrop of the water-bearing layer. If now from a point on the surface, at a level lower than that of the outcrop of the porous stratum, a drill hole be sunk to the water-bear ing bed. a flow- of water will be obtained, but the water will seldom rise to level as the point of intake owing to the friction which has to be overcome in flowing through the porous bed. The most favorable conditions are when the rocks form a basin, or when the inclined porous layer passes into an impervious one. The collecting area. or region drained by the porous stratum may be in the immediate vicinity of the well (a common case in shallow veils) or it may be at a distance of several hundred miles. In boring for artesian water a knowledge of the geological structure of the region is of highest importance. The work of the United States Geological Survey, aided by data contained from wells already bored, has demonstrated the existence of several ex tensive and •ell-marked artesian water-yielding areas. Thus a large part of Nebraska, South Dakota, eastern Colorado, and northwestern Kansas, obtains its artesian water from the Dakota sandstone, the collecting area of which is around the base of the Black Hills in South Dakota and along the eastern foothills of the Rocky Mountains. The Iowa wells derive their water from the Saint Peters sandstone, whose collecting area is in Wisconsin. Along the Atlan tic coast, many wells obtain a supply of pure water from the southeasterly dipping Tertiary and Cretaceous beds underlying that area.
Artesian wells in all parts of the country yield a supply of water for domestic use, which in many instances is much purer than surface water. In the arid regions of the West they also serve the purpose of supplying water for irriga tion. thus rendering fertile the soil of many dis
tricts heretofore non-productive.
The Chinese were acquainted with artesian wells, and in Europe they have been used for centuries—in France, England. Austria, and Germany; indeed, the basin-shaped structure of the Paris and London areas, with their alter nating beds of clay and sand, has yielded the type structures for artesian water supply. Por tions of the Sahara Desert have been reclaimed by artesian water derived from wells sunk by the French Government. The effect of these wells has been materially to benefit the country, and also to change the character and habits of its nomadic Arab inhabitants. Several tribes are said to have settled clown around these artificial springs, and, thus forming the centres of settle ments, to have constructed villages, planted palms, and to have entirely renounced their previous wandering existence.
Many artesian wells have been driven to a great depth, their diameters varying from three to six inches, several such deep borings having been mane in the United States; e.g., at Saint Louis, ?I°. ( 3843.5 feet) ; Columbus, Ohio ( 2775% feet.) ; Louisville, Ky. (208G feet) ; Charleston, S. C. (1250 feet) ; Galveston, Tex. (3071 feet) ; Pittsburg, Pa. (4925 feet). At Wheeling. W. Va., there is a dry well 4500 feet in depth, which has furnished valuable records of temperature changes in the earth's crust. Among the noted foreign wells is one at Passy. near Paris, 1923 feet deep: Sperenberg, near Berlin, 4194 feet; Schladenbach, near Leipzig, 5735 feet.
The temperature of artesian well waters is commonly about 40° to 50° F., except in the case of deeper wells, whosh waters may reach a temperature of 70° to SO°. In some places these hot waters are used for heating buildings. as at Grenelle, Paris. The Grenelle well-water has a surface temperature of 81.70° F.
Cases are not infrequent where artesian waters are charged with gases such as carbon dioxide, or hydrogen sulphide; or they may contain mineral substances in solution, thus at times serving as medicinal waters.
The methods adopted for boring artesian wells are similar to those employed in drilling oil wells. (See WELL SINKING.) The cost is com monly from $2 to $3 per foot for the first 1000 feet, and 50 cents greater per foot for each ad ditional 500 feet. Artesian wells commonly show a gradual decrease in flow, due either to partial filling of the tube, or to reduction of pressure because of the boring of new wells in the same vicinity, or to exhaustion of the basin. More precise information regarding the distribution and characteristics of the artesian waters of dif ferent portions of the United States may be found in the bulletins and annual reports of the United States Geological Survey and of the geo logical surveys of various States, particularly those of Iowa, New Jersey, Mississippi, and Missouri.