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

The chief advantages of a properly constructed and properly lo- cated ground- water supply over a surface supply are ujiiformly low and agreeable temperature, sanitary safety, and absence of dis- agreeable odor, color, or taste. The chief disadvantages are that the water may be more highly mineralized, the amount available may be inadequate, and the cost of construction and operation may be greater. The choice of a source of supply, the method of development, and adequate provision for extension of the system with increased consumption are matters in which communities should procure expert advice. ]^Iost ground-water systems for public supply comprise one or more batteries of driven Avells connected by suction mains to pump- ing plants which discharge into small reservoirs with distributing pipes. A few plants use dug wells or infiltration galleries. The dri\-en wells are similar to those described on pages 543-54-1:, except that they are in general of greater diameter than domestic wells. They are so located that they will draw from as great an area as possi- ble with the least amount of piping, but with consideration for the difference in the abundance of the supply throughout the field. If tlie direction of the underflov,- is kiiown. tlie lines of Avells are placed across it m order that tlie maximum yield may be intercepted witli- <»ut interference among the wells. 48 GROUND WATER IN NORV/ALK AND OTHER AREAS, CONN. In selecting- sites for wells it is essential to consider the character of the water-bearing formation. As a rule, only small supplies can be obtained from the till or from the underlying bedrock, but large supplies, such as are required for public waterworks, can be de- veloped in man}^ places from the extensive deposits of sand and gravel that constitute the stratified drift. These deposits and the surface features by which they can be recognized are elsewhere de- scribed. (See pp. 22-24.) The distribution of the stratified drift in the towns discussed in this report is shown on the maps (Pis. Ill, lY, andVI). A number of test wells should be sunk and should be vigorously pumped in order to determine the water-bearing caiiacity of the formation at different points and depths. The pumping should be as heavy and as long continued as possible, in order that any de- terioration in the quality or abundance of the water may be detected and so that as strong jdelds as possible may be developed. Analyses of samples collected at intervals and measurements of the yield should be made. The static level in open wells near the test wells should be observed before, during, and after pumping to ascertain the amount and extent of the drawdown of the water table and its rate of recovery. In order to get successful wells with large yields in the stratified drift, it is necessary to clean the wells out thoroughly and thus to get rid of the fine sand and to develop around the intake of the well a reservoir of clean gravel. The wells should be not less than 8 inches in diameter and should have casings extensively perforated with circular holes one-fourth inch or more in diameter or slits not loss than one-fourth inch wide. The wells should be pumped vig- orously for a long time, preferably with an air lift, but if an air lift is not available, by means of a centrifugal pump, in order to get out the sand. It is desirable in developing a well to pump it at its maximum capacity or at least considerably harder than it will be pumped when it is put into service. If this is done there will generally be not much trouble with sand when the wells are in use and are pumped at the more moderate rate. The methods of developing wells in incoherent and poorly as- sorted sand and gravel deposits, such as the stratified drift, are much better understood in the western part of the United States, where hundreds of thousands of acres are being irrigated with water pumped from such wells, than in the East, where there has in general been less need for large underground supplies. If the methods described above, which are extensively used with success in the West, were applied to the stratified drift, wells yielding several hundred GROUND WATER FOlI PUHLIC SlUTLY. 49 iralloiis a minute coiild no (1()ul)t be obtained in many places. If waterworks can be supplied by one well ol" laiire yield or even by ii few such wells the cost of maintainino; the wcdls and the eost of puiu])- ing will be le?-s than where there is a large battery of small wells hav- ing casings with small perforations or screens of fine mesh which generall}' become partly clogged and do not admit Avater freely. The source of the water may be rainfall on the adjacent region or underflow from some body of water, or in part from both. Water from a surface body is greatly improved in quality by passing slowly through a mass of soil. Water derived chiefly from absorption of rainfall by the soil has a temperature of 48° to 52° F., which is the general temperature of the earth below the depth of diurnal varia- tion. Surface waters are much warmer in summer and colder in winter, so that a wide range of temperature in the clriven-well water would indicate surface origin. The experience at many plants at which ground water is pumped into open reservoirs is that there is likely to be a heavy growth of algae, even more than where surface waters are thus stored. Eoofing the reservoirs is found to reduce or eliminate the algal growths, for they thrive only in abundant light. Roofed reservoirs also keep the temperature more uniform. As roofing is expensive, however, the usual practice is to have much smaller storage capacity and to de- pend on the pumps to keep pace with the fluctuations in consump- tion. An excessive amount of carbon dioxide, iron, or manganese in some supplies has been troublesome. Carbon dioxide has made a good deal of trouble at the plant at Lowell, Mass., and experiments were mnxle in 1914 to find a remedy.^ It was found that spraying the water under low pressure from small nozzles would aerate it and thus eliminate the gas. By another set of experiments, conducted at the same time, for the removal of iron and manganese which had increased in amount as the draft on the supply increased, the con- clusion was reached that " the iron and manganese can be successfully and economically removed by limited aeration, passage through a coke prefilter not less than 8 feet in depth, operated as a contact bed at a rate of 76,500,000 gallons per acre daily, and subsequent filtration through sand at a rate of a million gallons per acre daiW." The rate of filtration and the details of construction of the filter beds would be somewhat different with waters of different content of carbon dioxide, iron, and manganese. ^ BailK)Ui'. F. IT.. IinpvoA-cniPnt of the water supplj- of the city of Lowell, a special report to the iniinicipal council, 1014. 154444 "'— 20 4 50 GROUND WATER IN NORWiVLK AND OTHER AREAS, CONN. TYPICAL PLANTS. GREENFIELD, MASS. At Greenfield, Mass., o-round- water supply supplements the surface suppty.^ Near Green River a Avell 40 feet in diameter and 30 feet deep was made by sinking a cylindrical concrete caisson. The water level is only 5 feet below the surface, and the earth is loose and pervious. Pieces of 2^-inch pipe were placed in the concrete walls during construction in order to permit ready entrance of water. The well is covered by a domed concrete roof. At one time 2,000,000 gallons of water were pumped daily for about two weeks, though the pumps are generally run only part time and draw only about 1,200,000 gallons daily. HYDE TARK, MASS. The Hyde Park Water Co. formerly had a ground-water supply. The supply was drawn from 150 driven wells connected to a central eollectiiig chamber, and the water was pumped through the mains to a reserA'oir and stand]3ipe with a combined storage capacit}' of 2,000,000 gallons. The pumps had a capacity of 2,500,000 gallons a day, and there were 32.4 miles of mains, 1,806 .service taps, and 178 fii'e hydrants.- The original equipment, installed in 1885, com- prised 64 driven wells 2 inches in diameter, from 25 to 38 feet deep.'^ The wells were pumped in 1886 at the rate of 1,000,000 gal- lons a day for seven days. The water level was dei3ressed froin 8 to 15 feet below the surface — ^tliat is, it was lowered T feet — but recov- ered overnight. The pumps were unable to lower the level below 15 feet. LOWELL, MASS. Lowell's first waterworks, built in 1870, comprised a filter gallery 1,300 feet long parallel to and 100 feet distant from Merriniaclv River, from which water was pumped to a distributing reservoir. The supply was about 900,000 gallons a day (1875), and as the daily consumption became greater a supplementary supply was puuiped direct from the river and passed through a sand filter. Epidemics of typhoid fever in 1890 and 1891 necessitated a better supply. Test wells were driven at different places near the city, and finally a contract was awarded to the Cook Well Co. for a 5.000.000-gallon supph' to be obtained by driven wells along River Meadow Brook. Fortj^-five 6-inch wells of the open-end type. -17 to 67 feet deep, were ^ Meri-iU, G. F., Tho Greenfield waterworks: New Englancl Waterworks Assoc. Jeur., Juno, 1915, pp. 149-ir,0. 2 Baker, W. N., Manual of American waterworks, 1S97. 2 Discussion, in New England Waterworks Assoc. .Jonr., Sept., 1886. GROUND WATER FOR PUBLIC SUPPLY. 51