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

Xitrates may also be considered as indicators of contamination by sewage, for nitrogen exists in all excreta as nitrates or in forms readily convertible to nitrates through oxidation. Waters that contain more than 6 or 7 parts per million of nitrate should be looked on with suspicion and subjected to bacteriologic examination. A content of more than 12 parts per million of nitrate usually indicates gross contamination. Waters in which the total min- eral content is unusiuilly high may be approved though the nitrate is a little high, whereas in waters with a low total mineral con- tent less nitrate is alloAvable. In general waters that are high in both nitrate and chloride indicate contamination by human ex- creta, Avhereas waters that are high in nitrate but contain only a normal amount of chloride indicate contamination hj live stock. Although waters that contain less than 6 parts per million of chlo- ride are probably free from animal contamination, waters that have unusually little or no nitrate should be treated wdth suspicion, for sewage often contains denitrifying bacteria which destroy the nitrates and convert them to nitrites and perhaps to free nitrogen and am.monia. Because of the comparatively unstable character of the nitrogen in the nitrates, the nitrate content is a far less reliable indicator of pollution than chloride, w'hich is chemicall}'^ very stable. ^ Smith, H. E., Connecticut State Board of Health Kept, for 1002, pp. 227-242. Orf^iiry, U. E., ;mfl Ellis, I'. E.. I'mlfrcronnd-water r(<sources of (.'onnecricut : U. S. Geol. Survpy Water-Supply Paper 232, p. 108, 1909. 62 GROUND WATER Ilf WOEWALK AND OTHER AREAS, CONN. It is 2)ossible in general to locate the source of excessive chloride or nitrate by inspection of the surroundings of the well or spring from which the sample for analysis was obtained. In fact, it is often ])ossible on simple examination of the premises to predict that analysis will show excessive chloride or nitrate. In addition to making safe the location of a well, or spring by seeing to it that no potential source of pollution is near, precautions should be taken to prevent the entrance of surface wash. The ground around dug wells should be filled in and' tamped enough to make rain water and drippings flow away from them and not back into them. An excellent protection is a concrete apron several feet wide on ail sides of the well and sloping away from it. Cattle^ should be kej^t away from wells and springs by a fence, and the^' should be watered at a trough some distance away. Drilled wells should have the iron casing set firmly into the bedrock to prevent the entrance of shallow ground water, and the casing should extend a foot above the ground to keep out surface wash. A little extra care, labor, and expense in the protection of a w^ater supply will be well repaid by the feeling of safety gained, if not by the saving of doctors' bills and perhaps even of life. TABULATIONS. The results of the analyses and assays and the computations based on them are tabulated for each town included in this report. Tables of analyses and assays comparing the waters from the vari- ous water-bearing formations are given on page 64. Within each table the data have been grouped according to the geologic for- mation from which the waters were obtained, and the average amounts of each constituent are reported, together with the number of analyses or assays used in obtaining the average. Figure 12 is a graphic representation of the table comparing the groups of analyses. The analyses of dolomite water and beach-sancl water are not plotted except as they are involved in the general average of the 25 analyses. With the possible exception of the analyses of w^aters from strati- fied drift and till, the number of analyses available is too small to represent adequately the average composition of waters from tlie various water-bearing formations. As it is inadvisable to draw generalizations from these data regarding the quality of water by formations, the graph (see fig. 12) and tables of averages are pre- sented with that understanding and are not intended to be inter- preted as conclusive. The presence of carbonate in waters is dependent upon the con- dition of its chemical equilibrium with bicarbonate. As the (iROi'xn WATioi; loi; itiujc sri'j'LN (>3 64 GROUND WATER IN NORWALK AND OTHER AREAS, CONN. equilibrium is a variable, separate averages of carbonate and bicar- bonate are often difficult of interpretation. Thus it will be noticed in the table of averages of analyses that some of the waters con- tained no carbonate at the time of analysis, although it is possible that under certain conditions carbonate might be present in them. As a basis for more careful comparison of the waters it would be advisable to convert the bicarbonate into carbonate by dividing the figure for bicarbonate by 2.03. Averages of groups of analyses of waters from the icater-l)earing formations of the Nor walk, Suffiehl, and Glastonhurij areas, Connecticut. [Parts per million except as otherwise stated.] o jo ^^• m , M ^ ■3 o o o ■ ^ 2 ■rt fHo, 2r7 ^ ^ ■^ o M ^ 2 '^s Formation. d a i a 3 'o i ■a 1 li 03 f o ^5 o d +3^ — ' Kl a •3 CO o o o3'~' "o o |d s o a.S i o CO g 2 2 2; '^ Gneiss 26 17 0.65 14 13 IS 4.1 4 fi 8.2 18 2.7 0 48 77 17 14 4.4 6.2 0.22 .08 100 114 SO 64 72 78 23 49 2 Dolomite al Sandstone ?fi 3? 44 Q ?. 21 4 6 8?, 105 4 1 ? 8 960 1,50 170 57 3 Stratified drift 19 ■SO 13 3 7 17 0 49 19 13 7 0 119 48 64 45 10 Till ?3 m 14 5 5 15 P 70 14 8.7 3.6 115 59 75 39 8 11 21 .32 .32 22 18 6.0 5.1 37 17 .0 1.0 90 42 49 29 30 10 4.4 4.5 218 140 80 66 86 82 100 45 ol Average of 25 analyses a Only analysis available from this formation. Averages of groups of assays of iraters from the various irater-hearing fotma- tions of the Norwalk, Suffield, and Glastonbury areas, Connecticut. (Parts per million except as otherwise stated.] Formation. Hi so 03O csO ao «2 °.2 .CI eg is O in . <s a, o « O m.2 ■ W.J Gneiss Sandstone Stratified drift Till Average of 42 assays 0.32 .25 .22 .21 .22 3.3 4.0 .0 .9 76 135 44 109 48 8.6 17 12 17 204 193 113 161 129 52 96 125 153 77 120 102 42 TEMPERATirRE OF GROUND WATER. The temperature of ground water depends on and tends to become the same as that of the material through which it circulates. A layer a few inches thick at the top of the ground varies greatly in tempera- ture every 24 hours, owing to the heating effect of the sun in the da}^- time and the radiation of heat at night. This phenomenon is particu- GROU.XI) WATKIl FOR rUBLIC SUPrLY. 65 lai'ly noticeable early in the sprin^-, when the <i:r()iin(l Ireezes liai'd at night but tlunvs and beeomejs sol't and nuuUly (buin<>- the day. At a moderate depth these diurnal variations become negligible and only seasonal fluctuations oi" tem])erature occur. These seasonal fluc- tuations of temperatuie correspond to the freezing of the gi'oimd to a depth of several feet in the fall and the spring thawing of this ground, which has remained frozen through the winter. At a still greater depth there are not even seasonal fluctuations and the temperature is uniform the year around. The depth of this zone of no seasonal fluctuation of temperature is believed to be r»0 or 60 feet. Its temperature tends to be the same as the mean annual temperature of the locality, and water which circulates through it tends to have the same temperature as the mean annual temperature. In the southern part of tlie Xorwalk area the normal ground-water temperature is probably about 49.5° F., the mean annual temperature at New Haven, a place of similar situation.^ In the northern part of the Xorwalk area the normal ground-water temperature is per- liaps 1° lower because of the gi'eater elevation and the greater distance from the ameliorating influence of Long Island Sound. In the Suffield area the normal ground-water temperature is probably about 48.5°, the mean annual temperature at Hartford. This will also hold for the northern or lowland part of the Glastonbury area, but in the southern or highland part the normal ground-water temperature will be half a degree or a degree lower. In the region of no seasonal fluctuation of temperature there is a rather uniform increase of temperature with increasing depth, due to the internal heat of the earth. This amounts to 1° F. for every 50 to 100 feet increase in depth, so that deep drilled wells usually get slightly warmer water. Springs and wells whose waters have traveled a considerable distance in the zone of no seasonal fluctuation should have this temperature uniformly the year around. If the circulation has been in large part in the zone of seasonal fluctuation the water will be warmer in summer than in winter. It seems probable that springs on north slopes, where the heating effect of the sun is at a minimum, would be a little cooler than normal, and springs on south slopes, where insolation is at a maximum, would be a little warmer than normal. Because of this factor and because of the increase of temperature in depth, the actual temperature of the water is of less importance in determining whether Avater has circulated near the surface or at considerable depth than the uniformity of the tempera- ture the year around. • Summaries of climatolocacal data hy flections : U. S. Weatlior Bviroau P.ull. 2. pt. 2, sec. 105, p. 11, 1905. 1.54444°— 20 5 66 GROTJls^D WATER liV NORWALK All^D OTHER AREAS, CONJST. DETAILED DESCRIPTIONS OF TOWNS. DABIEN. AREA, I^OPULATION, AJTD INDUSTRIES. Darien is on the southern liorder of S'airfield County, between Stamford and Korwalk, Long Island Sound forms the south boundary and Noroton Kiver the Yv^est boundary. The east boundary m part follows Fivemile Kiver. The area of the town is about 13 square miles, of which 3 square miles, or about 25 per ceiit of the whole area, is wood.ed.