Ground Water in the Norwalk, Suffield, and Glastonbury Areas, Connecticut

In closed-end driven wells a drive point slighth' larger than the pipe is used to penetrate the ground. Above the point is a perfo- rated section through which the water enters. As the pipe is driven down sections are screwed on to lengthen it. The pipes are in g-en- eral from three-fourths of an inch to 3 inches in diameter, and the screens from 2 to 4 feet long. Open-end driven wells are made by driving a plain pipe which may or may not have a heavy cutting shoe attaciied to it. The material inside tlie pipe is removed by means of a sand pump or 1 ralmer, H. S., Ground water of the Soutliinston-Gi-anby area, fonn. : T'. S. Geo!. Siu-vcy Water-Supply Paper 466 (in press). -Turneaure, F. E., and Tai-^sell, n. L., Public water .'jupplies, pp. .sl8-.12o, ifiOO. 44 GROUND WATEE IN NORWALK AND OTHER AREAS, CONN. water jet. In the jetting method Avater is. forced down a small pipe inside the drive pipe, and as it rises it carries up the sand, silt, and smaller pebbles. The pipe is perforated either before driving or by special tools operated from the inside after driving. In the East rather small pipes are used, but in the West a special casing 10 or 12 inches in diameter made of sheet metal is often provided. Several kinds of pumps are used with driven wells. With domestic driven v\^ells of small bore the usual practice is to screw a pitcher pump to the top of the pipe. In some of the larger driven wells a deep-well pump is put down inside the drivepipe, and in others a specially constructed section of the drivepipe acts as the cylinder. A centrifugal pump is used in some of the western driven wells of very large size and heavy yield. Driven wells are suited to loose sands and gravels, in which caving would make trouble in digging wells. They are inexpensive and have the advantage that if they are unsuccessful the pipe may be withdrawn and used again in another place. One disadvantage of the smaller ones is the proneness of the screen to become clogged hj an incrusta- tion of mineral matter or by silt, and another is that grit may be drawn up with the water and score the working parts of the pump so that it works poorly. Wells of the large type are the best adapted for obtaining large supplies from the stratified drift or other sandy or gravelly deposits. They should be more largely used instead of the small types of driven wells where large supplies are required. Driven wells are not suited to till because the presence of boulders makes driving difficult or impossible and because the yield of the till is insufficient for a satisfactory supply. DRILLED WELLS. Drilled wells are in general deeper than dug or driven wells and in general obtain their water from cracks or fissures in bedrock. They are made either by a percussion machine (churn drill) or by an abrasion machine (core drill). A percussion drill has a long steel bar with a hardened and sharpened bit at the lower end which is worked up and down by an engine and pounds its way through the rock. At intervals the drill is withdrawn for sharpening and the debris is removed by means of a sand pump. Abrasion machines are built to revolve a hollow steel cylinder shod with diamonds or with chilled steel shot, which cut a circular channel surrounding a core. At intervals the drill is removed and the core broken into sections and extracted. The portion of the hole above bedrock is cased with steel or wrought-iron pipe, which should be driven into the bedrock and firmly set to prevent the entrance of surface water. Drilled wells in Connecticut ranffe from 4 to 12 inches in diameter, but most of RECOVERY OF GROUND WATER. 45 tlioni are G inches in dianiotor. The avcnioe depth of the 129 drilled wells tahi]late<l in this report is '213 feet. AA'here only modeiale amounts of water are needed a pump of the dee))- well type o})eratetl by hand or by power is hnnji' in the well. In some avcIIs ^^here large amomits of water are to bo raised fiom a great depth use is made of an " air lift."' Compressed air is forced <!own an air pipe and delivered near the bottom of a discharge i)ipe, :ind then expands and rises, bringing Avater with it. The delivery pipe may be hnng inside the well witli the air pipe alongside it {</. fig. 11), or the rock wall and casing may act as the delivery j)i]>e (7>. fig. 11). It is essential that the length of the submerged ]>ortion of the air pipe should be from 30 to 70 per cent of the dis- tance from the bottom of the air pipe to the point of discharge. In shallower wells the percentage of sub- mergence must be greater than in deeper wells. The pressure used ranges from ■20 to 100 pounds to the s<|uare inch and is often cal- culated at one-fifth to one- quarter of a pound for each foot of lift. The two great advantages of the air lift are that it has no moving- parts in the well Avhere they would be inaccessible in case of wear by grit in the water, and that it ma}^ be controlled and operated from a distant air-compressing station. The efficiency, hoAvever, is not very high in many installations. The success or faihire of drilled wells can not be predicted because of the irregular distribution of the water-bearing fissures, but the statistical studies of Gregory and Ellis show that drilling at any jKiint will probably procure a satisfactory supply. Among the '237 wells drilled in crystalline rocks in Connecticut studied by Ellis,^ only 3 Avells, or 1.24 per cent, are recorded as obtaining no Avater. A supply of 2 gallons a minute is considered abundant for domestic needs, though insufficient for industrial purposes. Among the 134 wells drilled in crystalline rock whose yield Ellis ascertained "only Figure 11. — Diagram showinj; two types of niv lifts. ^ Gregory. 11. E., aiul Ellis, E. E., Unclergrouncl-water resources of Connecticut : U. S. Geol. Survey Water-Supply Paper 32.3, p. 91, 1909. 46 GROUND WATEE UST ]Sr-GilWALK AXD OTHER AREAS, COjSrF. 17, about 12.45 ]>er cent, furnish less than 2 gallons a minute." It is probably a conservative estimate to state tliat not less than 90 iper cejat of the wells sunk in the crystalline rocks have given supplies sufficient for the use required. Wells may be unsuccessful not only as regards quantity but also as regards the quality of the supply. Along the shore in the Norwalk area are many drilled wells that have bracldsh water, which enters through fissm-es that open also to the salt water of the Sound. (See p. 69.) Althoug^h wells are reported by Ellis that obtain water at all depths from 15 to 800 feet, the largest percentage of failures is in wells over 400 feet deep. TMs is due to the less number of joints and their greater tightness in depth. J'rom a consideration of the gieater cost per foot of drilling and of the lesser probabilities of suc- cess it is concluded that if a well has penetrated 250 feet of rock without success the best policy is to abandon it and sink in another locality. Gregory,^ in v/riting of the wells drilled in sandstone, says that "of the 194 wells recorded, only 11, or 5.6 per cent, failed to obtain 2 gallons a minute, the minimum amount desired for domestic pur- poses." The average yield of 112 of these wells is "27| gallons a minute, the largest being 350 gallons and the smallest two-tliirds gallon." As with wells drilled in crystalline rocks, so with wells in sandstone, it is considered " good practice to abandon a well that has not obtained satisfactory supplies at 250 to 300 feet." SPRINGS. In developing a spring as a source of water supply it is advisable to make some sort of a substantial collecting* basin. No materials which may rot should be used. Eotting works in two ways to injure a vv^ater supply; it adds objectionable decayed organic matter and it weakens the walls and allows the entrance of surface water "which may be polluted. 2*fo spring slionld be so arranged that water is dipped from it, as this process may readily transfer pollution from tliQ hands. The reserA^^oir should be covered and a pipe provided to carry off the flow, as this method not only prevents pollution from the hands, but also prevents eontamination by animals around the spring. If a spring is used for watering stock a pipe and trough should be provided. In order that the water may enter readily the reservoir should be thoroughly jierforated or should be open at the bottom, but it should have stout, water-tight walls extending a foot or two above and be- low the surface to prevent entrance of surface wash. Where it is desired to use the full flow of the spring, the shape of th.e springy 1 Op. cit., p. 130. GKOl^XD WATEi; I'Oll ri'BLK' SUPPLY. 47 aroii ilet<^riiiine.s tho. shape of the iv>erv<)ii-, ^vhich will alloAV of nearly coiuplote i-eoovery. If only :i iiKHlerate supply is needed tho ivsei'voir may i>e of an\ convenient shai>e. Small spring's may be ileveloped by settijig a length of large piix? of concrete, iron, or viti-itied tile vertically in the ground. Such tile is superior to the \Yooden cask or box used at many springs because of its greater diiiability and lesser expense in the long run. Whatever the type of the reservoir it should be provided with a cover or roof that will eti"eetually keep out leaves, sticks, wind-blown dirt, and small animals. GROUND WATER FOR PUBLIC SUPPLY. INTKXJDUCTIOlSr. The use of ground water for public supplies is a comparatively recent development in :N'ew England. Though most of the people a century ago used ground water, wbicli was obtained on a small scale from dug wells and springs, tlie growing need for large sup- plies was met in most places by surface water. Since 1880. hovrever. ;\ number of waterworks which use ground water have been con- structed in jS"ew England, and doubtless more will be built in the future.