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

H'hore \\:i> in gvneral a JiuxloiaLi' oiowili u[> to Is-k), a marked de- crease from 1840 to 1870, and a rapid growth from 1870 to the present time. The decrease was due to the general eniigTation from (he agricultural districts of New Knglaml but may have been ac- centuated by tiio distance of the town from the first railroads. The subsequent groM-th is I he result of the completion of the railroad in 1870 and of the development of the region as a district of country residences. This development will probably continue and will be greatly stimulated if a projected railroad to connect ^vith the main line of the New York, Xew Haven & Hartford Railroad at Green- wich is eventually constructed. The principal settlement is the centrally located borough of Ridge- iield. There is also a small settlement, Titicus, a mile northwest of the borough. Branch ville is in part in the southeast corner of Ridge- field but spreads over into Redding and Wilton. Ridgebury is a small village in the north part of the town. There is a post office at Ridgefield and rural- delivery service to the outlying sections. There is also a post office at Branchville in Redding. The Danbury branch of the New York, New Haven t*c Hartford Railroad, opened in 1852, runs north and south along the east boundary and has stations at Brauch\ille and Sanford. The Ridgefield branch, a little less than 4 miles long, connects Ridgefield and Branch\'ille, and has stations at Florida and Cooper. An automobile stage line connects Ridgefield with Danbury. Tlie principal industry of Ridgefield is agriculture, and dairy products for the New York market form a specialty. The quarrying and grinding of feldspar and quartz have been carried on intermit- tently. Formerly there was also some manufacturing of cabinet work, shoes, hats, and tinware, but these industries died out about 1850 M'ith the oreneral change of industrial conditions. SFr.FACK FEATTEES. The characteristic features of the western highlands of Connecti- cut are better developed in Ridgefield than elsevdiere in the Norwalk area, because it is the most remote from the S'ound. In the south part of the town the broad, flat-topped hills are approximately 800 feet above sea level. Farther north the hilltops are approximately 1,000 feet, but in the extreme north part. of the town the hills are somewhat lower. The valle3^s between the hills are cut to different depths. It seems probable that this region was once eroded to a nearly flat surface. Subsequent uplift of the region rejuvenated the streams so that valleys have been cut below the old erosion sur- faces. Tlie valley north of Round Mountain and the valley of Titicus River, v.hich join just north of the village of Ridgefield, 96 GROUND WATER IN NORWALK AND OTHER AREAS, CONN. 0) o and their southwestwarcl continuation are underlain by limestone, which is relatively soluble, so that these zones have been deeply eroded. These valleys are characterized by wide and nearly level floors above Avhich rise st«ep w^alls with many bare outcropping ledees. The other valiej^s have only narrow valley floors. The valley south of Eound Pond is also of the broad-floored type and is underlain by lime- stone. Figure 15 shows a profile across Eidge- field drawn along a line bearing northeast which is indicated on the maps (Pis. II and III) by the line C\ It shows the two lime- stone, vallej^s cut below the upland areas of gneiss. The highest point in Eidgefield is Pine Mountain, the crest of which is 1,060 feet above sea level, and the lowest point is where Norwalk River crosses the south boundai^y at an eleva- tion of 330 feet. Mamanasco Lake occupies a depression on the flank of the valley of Titicus River at the foot of the north slope of Scott Ridge. Some- what similar depressions are to be found else- where in the limestone area but have been filled in. Most of the filling was probably done in late glacial times by debris carried by the great volumes of melt water from the glacier. Wells sunk by the Ridgefield Water Supply Co. in the swamp south of Round Pond gave the fol- lowing section: Alluvium, 40 to 60 feet; clay, 10 feet ; sand and gravel, 230 to 250 feet. This section may indicate that the melt water washed in 250 feet of sand, after which the supply of sediment decreased, and the basin became a lake, in the bottom of which 10 feet of clay was deposited. Finally 40 to 60 feet of alluvium has been carried in and the lake filled up. The clay layer must extend under all or nearly all of the swamp, as it effectually prevents any ° ^ entrance of water into the sands below it. Eidgefield occupies parts of six drainage basins. An area of about half a square mile in the northwest corner is drained by a small brook tributary to Still River which flows northward and enters Housatonic River near New Milford. The run-off of about 8 square miles in the northeast part of the town reaches Saugatuck River. Ten ^ oi BIDOKFIELD. 97 square miles in the east-central and southeast parts of Ridscficld :.ro included in the headwaters of N(irwalk River. The headwaters of Silverinine River drain about 3 square miles in the southwest part of the town, and just north is an area of 2 square miles tributary to Mill Jviver. which enters Long Island Sound at Stamford. Three square miles at the middle of the western margin of Ridgefield is drained by Waccabuc River, which flows into Cross River and so to Croton River and the Hudson. The west-central and northwest parts of the town are drained by Titicus River, which also is tributary to Croton and Hudson rivers. The borough of Ridgefield, then, includes paiiis of the basins of Housatonic, Saugatuck, Xorwalk, Silvermine, Mill, and Hudson rivers. ■WATKR-HEARING FORMATIONS. BefJrock. — Four varieties of bedrock have been recognized in Ridgefield.^ About 18 square miles in the north part of the town is underlain by the Becket granite gneiss. The original character of this rock is not certain, but it is probably essentially a metamorphic rock of igneous origin. It is a banded gray rock, composed of layers rich in biotite wdiich alternate with layers rich in the lighter-colored (ju.artz and feldspar. The segi-egation is due to the flowage under intense metamorphism and realinement of the grains under pressure. This structure is more developed in some places than in others, and there makes the rock readily cleavable. The bedrock of an area of 2 square miles in the southeast corner of the town is the Danburj^ granodiorite gneiss. It is a gray rock composed substantially of quartz, feldspar, and hornblende. Other minerals are present in minor amounts, and in some phases biotite (black mica) replaces more or less completely the hornblende. In one phase of the rock certain of the feldspar crystals are much larger than the other mineral grains and give the rock a porphyritic texture. The rock is massive but has a distinct gneissoid texture formed by the flowage concomitant with mashing during regional meta- morphism. Underlying an area of 7 square miles in the southwestern part of Ridgefield, and including most of the borough, is the Thomaston granite gneiss. It is similar to the Danbury gi^anodiorite gneiss except that hornblende is nowhere prominent, and the por]3hyritic texture is absent. The features of the Becket, Danbury, and Thomaston gneisses that relate to their carrying water are similar, and may be discussed 1 Oi-pgory, H. E., and Robinson, H. H., Preliminary geolosrical map of Connecticut: Connofticut Geol. and Nat. Hist. Bull. 7, 1907. 154444"— 20 7 98 GROUND WATER IN JSTOEWALK AND OTHER AREAS, CONN. together. A little water may be contained in the minute openings be- tween the mineral grains, but its amount is negligible. These rocks have been subjected to great and violent crustal movements which have opened fissures that in general form parallel systems whose directions depend on the direction in which the stresses acted. One system is horizontal or onlj^ slightly inclined, and is cut by one or more systems of steeply inclined or nearl}- vertical fissures. The rock is thus cut into polygonal blocks by the intersecting fissures and joints. Some rain water finds its way through the mantle of over- lying unconsolidated material into the intricate network of joints and crevices. Wells drilled into these rocks are apt to intersect, within a reasonable depth, one or more of these water-bearing fis- sures and thus obtain a moderate to abundant supply of water. Data on five such wells are given in the table on page 103. The Stockbridge dolomite underlies several valleys half a mile to a mile wide that aggregate 9 square miles in area. This rock is a light gray magnesiau limestone and is no doubt of marine origin. Much of the rock has been metamorphosed to a medium-grained, well- crystallized marble. The calcite and dolomite, of which the rock is essentially composed, yield under metamorphism and recrystallize as roughly equidimensional grains that are unlike the elongated minerals formed from sandstones, shales, or igneous rocks. The resulting texture is more massive. The marble is relatively soluble, so that solution channels are veiy apt to be made hj water circu- lating along joint planes and bedding planes. Water gets into such channels by percolation from the overlying soil and may in many places be recovered by drilled wells. The well of Mr. S. L. Pierponi: and the well at the Town Farm are of this type. Interstitial water plays only a minor part in marbles.