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

The territory was taken from Stamford and made a separate town in 1820. In 1910 the population was 3,946, an increase of 830 in the decade from 1900. The mean density of population is 312 to the square mile. The following table gives the population at each cen- sus and the per cent of change during the preceding decade: ropulatiosi of Darien/' Year. Popula- tion, Per cent ehaiige. Year. Popula- Per com tion. change. 1820 1,126 1,212 1,080 1, 454 1, 705 + 8 -11 + 35 + 17 1S70 1,808 1,949 2,276 3,116 3,946 + 6 1S30 isso - r ^i 18*0 1890 + 17 1850 190i> . 1860 1910 + 27 aCoanoeticut rvC,2;isi?r aad Maiiua!, 1915, ]}. GJ3. There has been grov* tli in every decade except that from 1830 to 1840. In the following decade, 1840 to IS'oO, there was an unusually large growth, due presumably to tlie opening of the New York & New Haven Railroad in 1849. During the last two decades tliere has been a relatively great increase in the population which is dependent in large part on the proximity of New York City. A number of extensive and beautiful residential estates have been established in Darien, and it is probable that this sort of development w^ill con- tinue. The growth for the next tew decades will probably be mod- erate and steady. Darien and Noroton are the principal settlements. Both have stations on the main line of the New York, New Haven & Hartford Railroad. A trolley line connects Stamford and Norwalk and runs through Darien. Post offices are maintained at Darien, Noroton, and Noroton Heights, and the outlying districts are served by rural delivery. The Boston Post Road, one of the State trunk- line highways, runs east and west near the south boundary of the town. About 4 miles of its length is in Darien, and it connects all the shore towns betv/een Bridgeport and Nevv^ York. In addition, there are about 60 miles of road worked by the town and a number of miles of semipublic roads privately maintained. The town roads r. S. GEOLOGICAL SURVEY WATEK-SUPPLY PAPER 470 PLATE VIII A. ESTUARY IN DARIEN, CONN. '^'■-i^<:X -'ik^^iy, ,.^' B. SECTION OF STRATIFIED DRIFT, DARIEN, CONN. liARIEN. <)7 are excelleiil ami are con.-truetod \n part oi' macadam and in pait of gravel. Tlie principal tntlu.stries of Darien are agriculture and oyslor farming. Tlie residential estates directly and indirectly furnish einplt)ynient to n»any of the inhabitanfs. SUIU'\\Ctl FEATURES. Darien, altliough it lies near sea level, must be included in the \vesteri\ highlands of Connecticut because of the character of its bedrock and tlie topography developed thereon. The strongly ridged and furroAved surface of erosion has been depressed and in part submerged. Small estuaries alternate with peninsulas and make a very irregular shore line. The maximum elevation, about 260 feet above sea level, is found on several ridges near tlie north boundary. A long cycle of erosion had reduced this regio)i to a plain. Sub- sequently this plain was uplifted and dissected, forming ridges and elongated hills that trend about north and south. The hills were somewhat worn' down and the valleys partly filled w^ith debris. In a strip of coimtry about a mile wide along the shore there are many small knobs of solid rock which rise above the water level of the bays and above the salt marshes. It is belie\"ed that since its glaciation the region has been depressed relative to sea level, that the bays and estuaries are drowned valleys, and that the peniiLsulas are partly submerged ridges. Plate VIII, A^ a view in the southeasteiii part of the town, shows an estuary bordered b}'^ salt marshes above wliich rise small, wooded, rocky hills. The eastern part of the tov.n is drained by Fivemile Kiver and the western by Xoroton River. The central part of the town is drained by Stony Brook and a second unnamed brook. These streams rise just beyond the north boundary of the town and are about T) miles long. There are also a few short brooks in the soutli part of tlie town that drain directly into the Sound. WATEK-BEAKINti FORMATIONS. Schist- and gneiss.- — Three bedrock formutions have been recog- nized in Darien ^ — Becket granite gneiss. Danbur}- gTanodiorite gneiss, and Thomaston granite gneiss. The Becket granite gneiss, which underlies a small area along the north portion of the Fivemile Brook boundarj''. is of complex origin — that is, it is a schist, into which a great deal of igneous material has been injected, thus altering its character. The rock consists of ill- 1 Gregory, H. E., and Robinson, II. 11., Prpliminary geological map of Conn«etieut : Con- necticut Geol. and Nat. Hist. Survey Bull. 7, 1907. t>8 GEOUXD WATER IN NORWALK K^B OTHER AREAS, CONN. defined alternating bands of gray schist and sheets of granitic and liornblendic material. The Thomaston granite gneiss is the bedrock in a small area in the northwest corner of the town and a larger area around and south of Noroton. Originalh^ it was gTanite composed essentially of quartz, feldspar, and mica with minor quantities of accessory minerals. Subsequent mashing has given it a moderately pro- nounced gneissic texture expressed by dark bands that are relatively rich in black mica. The degree to which this texture is developed varies from place to place. The Danbury granodiorite gneiss is similar to the Thomaston granite gneiss except that it has hornblende in addition to quartz, feldspar, and mica. Its gneissic character is in general less pro- nounced but is everywhere clearly distinguishable. This formation underlies most of Darien. The water-bearing properties of the three bedrocks are so much alike that they may be considered together. Interstitial water is almost if not entirely absent. A number of elongated openings, lissu.res, and joint cracks exist in these rocks. Water which has fallen as rain and snow and been absorbed by the unconsolidated mantle rock may be transmitted ultimately to the intricate net- work of intersecting fissures in the bedrock. Wells drilled into the rock are apt to intersect one or more such water-bearing crevices and to obtain moderate supplies. In general the fissures are more abunflant in the higher zones of the bedrock than farther down. It is therefore better policy to abandon a well that is unsuccessful in the first 300 feet arid to try in a new place, rather than to drill deeper. This is shown by the following table compiled from the data on drilled wells given on page 74. The wells have been grouped according to depth, and the ratio of the yield (in gallons per minute) to the depth computed. The number of gallons per minute obtained for each foot drilled is in general less in the deeper groups than in the shallower groups. Relation of yield of drilled 'nells to depth. Depth of wells (feet) - ■ Number of wells Total depth - - feet- Total yield gallons per minute. Average yield .do- - - Yield per foot of drilling do. . . 0-99. 100-199. 200-299. 300-399. 400-499. 7 8 3 3 5 o29 1,093 694 1,027 2,145 42.5 39 14.5 23.5 94 6 5 5 8 19 .080 .036 .021 .023 .044 500 and over. 4 3,468 32.5 7 .009 Tlie depths of 40 drilled w^ells in Darien were ascertained. They range from 65 to 1,465 feet and average 266 feet. The yields of 30 of DAKIEN. 09 these wells uverao-e 8 gallons a minute. A few of them yielded no water, and the oroatest yield was ^*0 g'allons a niinnle. No general statement can be made as to the direction and extent of the water-bearing fissnres in the town. Systems of fissures, or a set of two or three systems, are developed locally. One system is roughly horizontal and i?s cut by one or two steeply inclined fissure systems. One of the inclined systems tends to dominate the other. It is said that on the east side of Long Neck Point there is more probability of obtaining salt water in deep wells than on the west side. A pos- sible explanation of this condition is suggested in figure 13. A system of strong fissures striking north and dipping west would be likely to carry sea Avater in.to wells near the east shore, for the fissure cut by such Avells crops out under the Avatei's of the Sound. The fissures cut by drilled wells on the west side of the peninsula would be fissures that crop out above sea level, The out- crops of bedrock on Long Neck Point are so few tliat the direction of the fissure systems could not be ascertained. It is impossible to make a general statement as to 1k)w near the shore a well may be drilled with certainty of avoiding pollution b}^ sea water, because of the great irregidarity of the fissure systems. However, it seems inadvisable to drill within 500 feet of the shore, or on a small island. TJ7]. — Overlying the consolidated bedrock in Darien are found three types of mnntle rock — till, stratified drift, and the muds of the salt marshes, the last of which, however, are not an available source of w^ater suppl3^ Till is the material formed by the plowing and scraping action of the great ice sheet that overrode the region in glacial time. It consists of a thoroughly mixed mass of debris of all kinds of material in fragments Avhich range in size from the finest of rock-flour par- ticles to boulders weighing tons. It comprises a matrix of sand, silt, and I'ock flour in which are embedded pebbles, cobbles, and bouldei"s. Between the smaller particles are minute interstices that are capable of absorbing rain Avater, of storing it, and of giving it out sloAvly to wells aTid springs. AVells dug in till, unless unfavorably situated, Avill yield small but fairly reliable supplies of Avater. Forty-three Figure 1.' IT,vpi)thot!cal section of Long I'oiiit, DiU'it-n. Nock 70 GROUjSTD V/ATER IX iNTORWi^iK AND OTIIEE AREAS, GONlv, suck wells were measured at Darien in September, 1916. Data re- garding the depths found are given in the following table : Siii)iina>-[i of vjeUs dug in till in Daricii. Total Depth to depth. water. 1 Depth of water. Feet. 55.0 6.7 19.6 Feet. 35.0 3.1 13.3" Feet. 20 0 & 4