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0.60 parts; the third group, those in which the excess of chlorine is over 0.60 parts. The first group contains the springs deriving their supply from water-sheds with little or no population ; the second group, those in a moderately populated area ; and the third includes the springs which are located in regions with considerable population.

Normal waters have been defined to be those which have not received any waste products of human life. They are as a rule confined to the water-sheds without population. Any excess of chlorine above the normal of the region in which the water is found is a measure of the amount of waste products, human and animal, that the water has taken up. But the evidence of contamination based on the chlorine alone does not tell us whether the source of pollution is near by or remote. This information is obtained from the determination of the nitrogen, which in freshly polluted water is present in the form of organic matter (albuminoid ammonia) and free ammonia, while in water which has percolated under favorable conditions through porous ground the nitrogen is all oxidized and appears in the form of nitrates.

In interpreting the analyses of the waters in the following classification, it is necessary to take into consideration the degree of purification which has taken place in those waters which are shown by their chlorine contents to have been at some time more or less contaminated. It is easily possible for a spring water which has somewhere in its course received a large amount of polluted drainage to be organically much purer than another in which the amount of contamination has been much less. The purifying power of porous ground, in which organic matter is exposed to bacterial action with access of air, is sufficiently great, under favorable conditions, to convert completely organic into mineral matter, as far as chemical analysis can indicate. It will be seen in the accompanying analyses that some of the waters which have received a large amount of pollution, and which may be said to be to a considerable extent filtered sewage, have less organic matter remaining in them, as shown by the albuminoid ammonia, than others in which the degree of contamination was originally much less.

In the process of filtration through porous ground, whereby organic matter in water is oxidized, there may also be effected a purification as regards disease germs. This latter and most important purification may be due to the removal of the germs by the mechanical straining of the water at an extremely slow rate through the ground, or to the death of the germs, owing to unfavorable conditions for their life in the filtering process.

While we cannot always know in any particular case which of these processes may have been the principal factor in the purification of the water, we know that the conditions of perfect mechanical filtration (whereby all suspended matters are removed from the water), and the conditions of perfect chemical purification, are those also most favorable for the complete removal of bacteria.

Although water badly contaminated with sewage or the wastes of buman life may be purified by thorough filtration so as to be free from organic matter and from bacteria, yet in cases of ground waters of this origin and character we seldom feel complete security, that the conditions of perfect filtration will always exist. A long-continued rainfall, for instance, may result in more rapid filtration and consequently less perfect purification; or the creation of new sources of contamination, nearer the spring, may result in its dangerous pollution.

It is for such reasons that a certain suspicion always attaches to ground waters which have at any time in their history been seriously polluted. The use of ground waters, whether springs or wells, in built-up communities, should therefore be avoided, for we have no control over the conditions of filtration, and have no means of knowing (except by constant vigilance in the examination of the water) when a water hitherto well purified may become injuriously impure. The danger from the use of ground waters in populous regions increases with the increase of population, and with the nearness of the sources of pollution to the spring or well.

No attempt was made to determine the species of bacteria in these spring waters, and the numbers of bacteria given in the tables are not, therefore, to be interpreted as expressing in any sense the relative fitness of the waters for drinking. In open wells, for instance, we may often find a large number of harmless bacteria which have come from the air or from dust, and which would not be found in the water if better protected. A favorable construction is, of course, to be put on the low numbers of bacteria, since they show that few bacteria of any kind are present, and that the conditions under which the water is filtered in the ground are favorable to its purification.

Normal Spring Waters, and those in which the Chlorine is not more than 0.20

Parts per 100,000 in Excess of the Normal.

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7139 Arlington, . Robbins,

6.60 .0000 .0000 7396 Belmont,

Belmont Naturais 9.00 .0000 0000

Mineral. 7436 Boston,

Allandale Mineral, 5.30 0000.0022 918+ Framingham, Nob-cot Mountain, 3.55 .0004.0000 7492 Holbrook, White Rock,

3.90 .0000 0084 033 Lawrence, Cold,

.0040 .0006 6633 Lowell, Sheeprock,

2.50.0002.0010 7401 Medford, Fulton Natural,

4.40 0000 .0000 7395 Medford,

Middlesex Mountain, 6.30 0000 .0018 6519 Methuen, Olis,

.000.0030 7455 Milton,

Blue Bill Silver,

2.30 .0002.0002 7406 Lyon,

Echo Grove Mineral, 6.25 .0004 .0024 7397 Chelsea,

Mount Washington, . 10.30 .0000 .0000 7434 Stoneham, Cedar Park Mineral, 4.90 .0000 .0012 7484 Lowell,

Mount Pleasant, 4.40 .0000 .0004 7471 Brockton, Indian,

3.00 .0000 .0000 7415 Lynn, Electric,

4.05.0000 .0002 7514 W. Springfield, :/ Massaroit,

5.50 .0000 .0000 7488 Stoughton, . Crystal,

3.00 .0000.0004 7191 Whitman, Goulding's,

3.90 .0000 .0000 7472 Brockton,

Brockton Mineral, 3.80 .0000 .0006 7481 South Easton, Simpson's,

3.70 .0000 .0008 7465 Went Abington, Highland, .

5.60.0000 .0020

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Spring Waters in which the Excess of Chlorine above the Normal is from 0.21 to

0.60 Parts per 100,000.

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Spring Waters in which the Excess of Chlorine above the Normal is over 0.60

Parts per 100,000.

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7435 Stoneham, .
7402 Lexington, .
6632 Lowell,

Brockton,
Brockton,

Ererett,
7393 Everett,
7420 Swampscott,

Everett, 1391 Everett, 7419 | Swampscott,

Chapman's Cr. Min., 10.70 .0000.0012 61 .4500.0000 .0090 2.86
Commonwealth Min., 11.90 .0000.0000 .61

.4200 .0000

.01:30 3.90 Leland Mineral, 12.90 .0008.0032

.3300.0000 .0300 4.86 Union,

9.00.0000.0000

.75

. 4500 .0001 .0150 2.73 Crystal,

10.20 .0000

.0010 .88 .4000 .000 0.0270 2.86 l'artridge, .

20.35 .0000.0000 1.51 .9000.0000 .0240 6.00 Everett Crystal, 20.25.0000 .0018 1.57 1.0000.0000 .03206.43 swampscoit Mineral, 23.00 .0002.0032 1.65 .7200.0003 .0210 8.00 Belmont Hill,

23.55.0000 .000S 2.18 1.1500 .0001 .0250 8.88 Glendale,

16.30 .0000.0006 2.29 .4000.0000 .02:30 5.71 Moose Hill,

21.90 .0002.0008 2.65 .7000.0001 .02709.13

15

2 40 18 35 59 146 81 85 35 20

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DESCRIPTION OF THE SPRINGS AND THEIR SURROUNDINGS. Arlington, Robbins Spring. -- About two thousand feet south from the corner of Brattle and Main streets. Stoned and cemented reservoir, five feet wide and six feet deep, covered by a small house. The water, which enters from below, from ledge, is three feet deep and a little lower than the surrounding ground; it is said to overflow all the year round. Surface water is excluded. The spring is at the eastern base of a rocky hill covered with wild shrubs and trees. No pasture within four hundred and fifty feet above. The natural drainage is east, towards Main Street. No buildings on drainage area. The grounds about the spring are resorted to considerably on holidays. Water is sold in Boston, Somerville, Arlington and Cambridge.

Belmont, Belmont Natural Mineral Spring. – This spring is in a valley in a large grassed farm, with considerable underlying rock, covered by loam, ahout half a mile from Lexington, on J. H. Cotton's estate, and about twelve hundred feet east of his Winter Street buildings. The water rises nearly to the surface of the ground into a reservoir four feet wide and two and a half feet deep, hewn in solid rock, and covered by a stone arch. Surface water is excluded. Drainage from north and west chiefly. No dwelling-houses on drainage area except possibly the Cotton buildings, five hundred feet west, considerably higher than the springs; manure heaps under barn one hundred feet farther. But all the drainage from these buildings would probably flow south, away from the spring. No top-dressing on farm nearer than three hundred feet, and this is on the east side, where the drainage is probably away from the spring. Market garden, with exposed manure heaps, seven hundred and fifty feet north of spring, which also probably drains away from the spring. A few flower beds around the spring and a little higher, the nearest being forty-five feet, on which a little barnyard manure is used. Pasture five hundred feet north of spring on drainage area. Water is sold in Boston, Waltham, Newton, Lexington, etc.

Boston, Allandale Mineral Spring. - On Allandale Street several hundred feet south from Centre Street, Jamaica Plain. The water rises to within two feet of the surface, in a reservoir seven and a quarter feet in diameter and four and a half feet deep, with stoned and cemented sides and rock bottom. The reservoir is in a small house ; surface water excluded ; iron pipe ; considerable overflow at time of collection. The formation around the spring is mainly gravel and conglomerate. The general direction of the ground water flow is south. The land north of the spring is covered with wild shrubs and trees to a distance of four hundred and fifty feet; beyond are partly grassed fields and pasture land. No buildings on the drainage area within one thousand feet.

There is a privy a few hundred feet south, and a little higher than the spring, but there is a dry run between, a little lower than the spring, which would probably lead away any drainage. The grounds around the spring are sometimes used for picnics. The water is sold in Boston, Jamaica Plain, Brookline, etc.

· Framingham, Nobscot Mountain Spring. - Large spring at base of ledge east side of Nobscot Mountain. Cemented reservoir, five feet by nine feet and five feet deep; covered by small house ; water flows by gravity through block-tin pipe to filling station filty feet below. Water-shed heavily wooded except directly above spring, where two or three acres have been cleared; no houses on watershed; used for pasturage to a limited extent. Water sold in Framingham and Boston.

Holbrook, White Rock Spring. - About half a mile from Plymouth Street, a mile from Holbrook Centre. Stoned reservoir, two feet in diameter, three feet deep, one and one-half feet depth of water. Surface water not excluded; no cover; no pump.

Said to become dry at times. Flow of water from south-west ; no houses in that direction for a mile or more. Drainage area covered by wild growth; no pasture land. Water sold in Ilolbrook.

Lawrence, Cold Spring. An open spring in sandy soil; no houses in tlie immediate vicinity, none on the slope back of the

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