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

sr=.SiO,+H The value of silica was taken arbitrarily as 25 parts per million, as in the computation of total solids. The unknown Init variable ratio between calcium and magnesium introduces a further error. ^ ld«m, p. 6.5. See also Water-Supply Paper S75, pp. H33-164, 1916. - Op. cit., p. .57. 3 Idem, p. SI. * Idem, p. 66. GROUND WATER FOR PUBLIC SUPPLY. 55 Tlie rosultfci arc tliereloiv reported to tlio nearest 10 il' above 100 and to the nearest 5 if below 100. The same formula was used for coinputino- foaming Inoredients ill the assays as in the analyses. Formulas upon which the classifi- cation of waters for boiler use as regards their corrosive tendency are based arc ditfcrent with the assays from those used with the analyses. (See section on interpretation of analyses, p. 57.) PROBABLE ACCURACY OF ANALYSES AND ASSAYS. The analyses in this report were all made accoi'ding to the meth- otls outlined in "Water-Supply Paper 236/ which gives also a discus- sion of accuracy of methods and results based on both theoretical and practical considerations. The subjoined table, taken from this dis- cussion, gives the limits which have been used for rejecting analytical data. Acceptance or rejection of analyses in which sodium and po- tassium (Na+K) are calculated is based on the difference between the sum of the constituents and the total solids. The sum is com- puted by adding the amounts of the various constituents, first con- verting bicarbonate to carbonate ^ ^.-, ' :CO,. Differences between the sum and total solids greater than the limit set forth in the above table are generally due to inaccuracy of work or errors of computation, though the presence of organic matter may cause seri- ous differences. Combining or reacting values have also been used to check analyses in which sodium and potassium have been determined. The percentage difference between the reacting values of the acids and bases is computed and compared with the proper figure accord- ing to the total solids in the table. Analyses showing errors greater tlian the limits given by the table were rejected or the waters were reanalyzed. Criteria for rejcctiiir/ (nialjitical datfi. Dissolved solids (parts per million). Maximum excess of total dissolved solids over sum of constituents (parts per million). Maximum excess of sum of constituents over total dissolved solids (parts per million). Maximum error of combining values (i>er cent). Not less than - I,ess than— 1 .50 15 100 20 200 30 500 40 1 000 ^ 5 6 8 12 15 5 4 3 2 50 100 200 .500 1,000 2,000 1 > Dole, R. B., The quality of surface waters in the United States, pt. 1, pp. 9-2.3, 28-39, 1909. 56 GROUND WATER IN NORWALK AND OTHER AREAS, CONN. Assays are approximations which serve to show, by means of a few determinations rapidly made and by computations based on these determinations, the general character of a water rather than the exact amount of each constituent present. It has been shown that the values of a water for domestic, irrigation, and boiler use may be determined by such assays with a degree of accuracy which is sufficient for practical purposes.^ CHEMICAL CHARACTER OF WATER. The essential points in describing the chemical character of a water are, first, the concentration or total amount of mineral matter contained therein and, second, the nature of the chief constituents. As regards the bases present the most important distinction is that between calcium and magnesium on the one hand and sodium and potassium on the other. Calcium and magnesium are members of the chemical group known as alkali earths and have many similar properties, so that they are in contrast with sodium and potassium, which belong to the group of alkali metals and are in turn mutually closely related. As regards the acid radicles present, distinction is made between the carbonate, sulphate, and chloride radicles. As carbonate and bicarbonate are always in chemical equilibrium and carbonate is the more stable, they are grouped together, and bicar- bonate is reduced to carbonate by dividing by 2.03. The acid and basic radicles are not balanced against one another directly but are lirst reduced to reacting values by multiplying by the valence and dividing by the sum of the atomic weights of the constituent atoms. The reacting values of the several acid and basic radicles are com- pared and used in applying the following classification : ^ Classification of water liij chemical charactet'. [Carbonate (CO3) Calcium (Ca)l U,^^,^,.^^^ (SO.) Sodium (Na) / [chloride (CI) The designation " calcium " indicates that calcium and magnesium predominate among the bases, and " sodium " indicates that sodium and potassium predominate. The designation " carbonate," "sul- phate," or " chloride " shows which acid radicle predominates. Combination of the two terms classifies the water by type, and the classification can be abbreviated by the use of symbols — for example, "■ Ca-COg " for a calcium-carbonate water. ^ Mendenhall, Vv. C, Dole, R. B., and Stabler, Herman, Ground water in San Joaquin Valley, Calif. : U. S. Geol. Survey Water-Supply Paper 398, pp. 43-50, 1916. - Idem, p. 80. GROl'Xl) WATEll FOW Pl'BLIC SUPPLY. 57 INTERPRETATION OF ANALYSES AND ASSAYS. Ill additioii to the cheiiiical clnssilicnl ion disfu^scd in (ho precod- \\\iX section, tlic inialyses and a.ssay> havr been inteii)i-eted as regaixls their suitability for boiler and domestic use. Mfnifdlization- and hardness-. — Waters may be classilicd accord- iniT to the concentration of dissolved niattei- in them — that is. the de^roe of mineralization — and according to their har(biess or soap- consuming powers. Waters may be considered as low in mineraliza- tion if they contain less than 150 parts per million of dissolved solids; moderately mineralized if they contain from 150 to 500 parts l)er million; highly mineralized if they contain from 500 to 2,000; and very highly mineralized if they contain over 2,000 parts per million. - Hardness in water is due chiefly to the presence of calcium and magnesium, which unite with soap, forming insoluble compounds that have no cleansing value. Hardness is measured by the soap- consuming capacity of a water and can be expressed as an equivalent of calcium carbonate (CaCOg). It can be computed from the amounts of calcium and magnesium in the water or can be deter- mined by actual testing Avith standard soap solution. Waters that contain less than 50 parts per million of hardness measured as cal- cium carbonate may be considered very soft; waters that contain from 50 to 100 parts, soft ; w^aters that contain 100 to 300 parts, hard; and waters that contain over 300 parts, very hard. Qualify for hoiler nse. — Three kinds of trouble in the operation of boilers are due to unfavorable features of the water — the formation of scale, foaming, and corrosion. Scale is mineral matter deposited witliin th.e boiler as a result of evaporation and heating under pres- sure. These deposits increase the consumption of fuel, as they are })ad conductors of heat, and they also decrease the cubic capacity of the boiler. They are a source of expense and a potential cause of explosions. Scale is formed of the substances in the feed vrater that ;ire insoluble or that become so under the usual conditions of boiler operation. It includes all the suspended matter, the silica, iron, aluminum, calcium (principally as carbonate and sulphate), and uiagnesium (principally as oxide but also as carbonate). Formulas for the computation of scale-forming ingredients are given on page 54. Foaming is the rising of water in the boiler, particularly into the steam space al)Ove the normal Avater level, and it is intimately con- Tieited with priming, which is the passage of water mixed with steam from the boiler into the engine. Foaming results when anything pre- 1 Idem, p. 82. 58 GROUND WATER IN NORWALK AND OTHER AREAS, CONN. vents the free escape of the nascent steam from the Avater. It is be- lieved to be due principally to sodium and potassium, which remain in solution after most of the other bases are precipitated as scale and which increase the surface tension of the water. The increased sur- face tension tends to prevent the steam bubbles from bursting and escaping. Other factors undoubtedly affect or cause foaming, but sodium and potassium are the chief agents. The principal ill effects of foaming are that the water carried over with the unbroken steam bubbles may injure the engine, and that it may cause dangerously violent boiling. Where waters that foam badly are used it is neces- sary to "blow off " the water at frequent intervals to get rid of the rather concentrated sodium and potassium. A formida for comput- ing the amount of foaming ingredients is given on page 54.