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Show 714 GROUND WATER RIGHTS IN SELECTED STATES basalt or aquifer that underlies the caprock and extends inland from it con- stitutes one underground reservoir, the water in different portions of which is seeking to find a common level. But that part of the reservoir that lies inland from the caprock is, obviously, not confined by an overlying impervious stratum; it has what is called a "free" water table. This means that if a well is driven into that area of the water-bearing stratum, the water cannot rise naturally in the well above the free water table-for the reason that there is no natural pressure or "artesian head" that would force it to do so. The free water table encounters the caprock along a line inland from and running in the same general direction as the seacoast, but not necessarily parallel to the shoreline. From that inland line seaward, the water is depressed because of the impervious character of the caprock-it is forced to stand below the level of the free water table inland from it and hence is under hydrostatic pressure. If a well is driven through the caprock and into the common water- bearing stratum in that area, the water will rise naturally in that well-it will rise in this artificial opening above the level to which it has been depressed by the caprock. Such water is called "artesian" water and such a well is an artesian well. The upper level, or highest point to which the water will rise naturally in such an artesian well, is called the "piezometric surface." Pressure on these bodies of confined water, exerted by the inland body of basal water that supplies them, causes water to escape from the confined strata through all available avenues. Water may escape naturally through overflow springs at the top of the caprock, by leakage through the caprock, and pre- sumably through submarine springs at the base of the caprock. Water may also be induced to escape from the artesian structure by artificial means; that is, by development or improvement of natural springs on the surface but principally by wells. Artesian wells. -Where the piezometric surface is above the ground surface, the water of a well drilled into the water-bearing stratum will flow upon the ground. But where the piezometric surface is below the ground surface, the water will not flow from such a drilled well because it cannot rise naturally to that height. Such a well is an artesian well, despite the fact that it does not flow upon the surface, for it contains artesian water that rises in the bore hole to the piezometric surface. To be put to use, of course, the water must be pumped to the surface. Inland from the line of contact between free water table and caprock, a well may penetrate the same body of ground water of which artesian water is a part. The water of such a well is not under pressure and is not artesian water. Isopiestic areas. -Alternating ridges and valleys extend from the mountains down to and under the coastal plain. Under this plain, a buried ridge extends from each major exposed ridge; the same applies to each major existing valley. These buried valleys were filled with relatively impervious sediments, forming dams separating buried ridges of pervious water-bearing rock. The piezometric surface within each area differs from that of the others, but throughout each |