I. M. de Varona found that the amount of ground water recovered from Ridgewood drain age area of 65.4 square miles in 1890, when the rainfall was 52.15 inches, was 17.68 inches, which was 33.9 per cent of the former. For several years in that area such amount ranged from 34 per cent to 33 ner cent of the pre cipitation. The Board of Water Supply esti mated that, if the Ridgewood watershed were completely developed, the yield of ground waters in normal rainfall years would be nearly 1,000,000 gallons a day for each square mile of area. They reported that the old watershed was yielding 900,000 'gallons a day per square mile and the new one was yielding 700.000 gal lons a day per square mile. The Burr-Hering Freeman Commission from its investigations concluded that, in addition to the water being pumped in 1903 for Brooklyn, there might be obtained 200,000,000 gallons per day from the southern watersheds of Long Island.
The underground reservoirs of California are structural basins filled with the alluvial debris, due to the weathering of the adjacent mountain ranges. Through such alluvial de posits precipitation percolates to the impervious rock below. The ground waters are thus col lected and their only escape is through some possible subterranean or known surface channel, evaporation or springing or seeping through the overlaying deposits at the lower side of the tilted, but elevated, basin. Such ground waters may be used and in some mountain localities are being drawn and conducted to irrigate des ert areas and to supply needy communities with wholesome waters.
The report of the State Water Conference of California in 1916 shows that many of Cali fornia's water problems were considered and recommendations made for drawing upon the ground waters in the San Joaquin and Sacra mento valleys and elsewhere to irrigate the arid lands where there is insufficient precipitation to make such lands productive and also to supply waters for municipal purposes.
The extent and quality of some ground waters are shown in the Water Supply Papers of the United States Geological Survey as fol lows: for Connecticut in Paper 232, for Kan sas in Paper 273, for Iowa in Paper 293 and for Owen Valley, California, in Paper 294.
Some of the legal principles applicable to ground waters in Europe and America are stated in Bradford Corporation v. Ferrand, 2 Ch. 655; also fully reported in two British Rul ing Cases. 980; The People v. New York Car bonic Acid Gas Co.. 196 N. Y. 421; Lindsley v. National Carbonic Acid Gas Co.. 220 U. S. 61; and in the annotations to the first of said cases and in the other cases referred to in said cases. Consult Water Supply and Irrigation Paper No. 122,' United States Geological Survey.
The Board of Water Supply of New York reported in 1912 that the Brussels watershed of 4.6 square miles yielded 2,100,000 gallons a day; that The Hague sand dune catchment area of 7 square miles yielded 5,100.000 gallons a day; that the Amsterdam sand dune catchment area of 11.6 square miles yielded 6,100,000 gallons a day, and that the Muhlthal watershed of 14.7 square miles yielded 21,300,000 gallons a day.
These few records indicate the large quan tities of ground waters obtainable from the watersheds mentioned for water supply pur poses. They also indicate the quantities of per colation into the strata of the areas described. They also indicate the amount of water stored in the earth's strata for water supply Some of the ground waters, however, find their way to the surface by seepage through sands and gravels, emerging in ponds, streams and springs. Such seepage is the outflow through she surficial layers of ground waters flowing downward from the water-tables above. Wher
ever the ground water level is higher than the surface or depressions in the surface, the water `seeps' through the sands and gravels and ap pears as already stated. This is noticeable in marshy areas in the period of heavy rainfall and also in the many mineral and other seepage sprirms found in mountainous districts as well as in such streams as those on Long Island. The amount of ground water thus returned to the surface is but a small percentage of the volume of underflow, the amount and rate of which in some localities have been determined and reported by Charles S. Slichter of the Geological Survey. The winter flow of Minne sota streams is largely seepage waters.
Ground waters are being continuously review abed by percolating waters coming from pre agitation, the amount of which the world over aunt be known to ascertain the volume of sur face and ground waters available for the water supplies of the inhabitants of the earth. They are also replenished to some extent from sur face waters in some regions.
Percolating waters descend to the surface of the saturated strata and become part of the permanent ground waters of the region. The saturated strata known as 'water-bearing for mations' are several hundred feet in thidoiess mid overlie the strata that are impervious to water. The surface of saturation is known as • level' and may be within a few of the surface. Above this saturation is not constant. Hence, to insure a continuous supply wells must be deep enough to reach the water level, and as that fluctuates in reat regions and is the wet and dry seasons, it is necessary to drive wells some distance below the level. From the several water hori mos, comprising strata, consisting of differ ent geological formations, various qualities and quantities of water are obtainable. Geological and water supplies reports of this and other countries may be consulted for specific informa tion in relation to the nature of the ground waters of any region covered in such reports. Myron H. Fuller and others of the United States Geological Survey have compiled much trainable data on the ground waters of the United States of America. From their reports as well as from others it appears that the water-bearing horizons are not always hori aontal, but incline either up or down in most watersheds, and the force of gravity causes a Row of ground waters between the layers of such bonzons. •mainly.° says Herbert E. Greg ory, •in the same direction as the slope of the surface.' Such flow is very slow, being frpm a few feet to a mile or more a year. depending on several conditions, such as character of the water-bearing formations, temperature, slope, and other physical elements. The however, is continuous and replenishes well;„ springs and streams, as they are drawn or otherwise discharge their waters.
and flowing wells exist in Connecticut, Iowa, California and elsewhere These and thousands of other wells in all lands are fed from the inexhaustible ground waters of the earth to supply human needs. Copen hagen draws its entire supply from wells down through glacial drift to chalk deposits.
Some of these may be hereinafter mentioned.
as they are the principal sources of the water supply of most rural populations.
Water supplies are obtained from waters that run off from catchment areas and from waters that percolate the strata of the earth. Before considering any particular water sup ply and a few only need be considered as they are necessarily local and special in their char acteristics, may be considered the important matter of the purification of water supplies. That subject is of general interest to all com munities.