Popular Science Monthly/Volume 11/August 1877/Bad Odors in Reservoired Drinking-Water
|BAD ODORS IN RESERVOIRED DRINKING-WATER.|||
THE citizens of Rochester were much inclined to congratulate themselves—and certainly on excellent grounds—when they had brought water thirty miles from the crystal depths of Hemlock Lake for the use of the city. But last year, to the astonishment and disgust of the people, their water became so offensive as to give rise to grave apprehensions respecting its effect on public health. In October it suddenly began to emit a peculiar fish-like odor, which continued until the following December. It was a very natural suggestion that this odor must be due to the presence of fish, which had somehow found their way from the lake into the main pipes, and thence into the smaller service-pipes, where their progress had been arrested, and they were undergoing slow decomposition. It is well known to those familiar with the experience of other large cities, that similar annoyances are by no means uncommon elsewhere. Regarding this we learn that "not long after the introduction of the Croton water into New York, and of the Cochituate water into Boston, the fish-like odor prevailed for some time to a most disagreeable extent. While this odor is of most frequent occurrence, others of very different character are occasionally reported. Last year the Bradlee Basin, which supplies a part of the water for Boston, became affected with an odor described as closely resembling cucumbers. None of the other ponds in the neighborhood were similarly affected. About the same time the water of Springfield, Mass., exhaled the odor of green corn. In 1874 the water of Cherbourg, France, became intolerable from an odor undistinguishable from that of a pig-sty. This same odor occurred last summer in Horn Pond, from which East Boston and Charlestown are in part supplied. The odor of decaying wood is not uncommon, especially in early summer." And, in response to a circular letter sent to the various cities of the United States and Canada, the author learned that the fish-like odor was far more prevalent than he had previously supposed, it having occurred in all the following cities: Concord, N. H.; Keene, N. H.; Burlington, Vt.; Boston, Mass.; Lowell, Mass.; Holyoke, Mass.; Brookline, Mass.; Springfield, Mass.; New Haven, Conn.; West Meriden, Conn.; New Britain, Conn.; Hartford, Conn.; Auburn, N. Y.; Newburg, N. Y.; Poughkeepsie, N. Y.; Trenton, N. J.; York, Pa.; Baltimore, Md.; Norfolk, Va.; Nashville, Tenn.; and St. Paul, Minn.
In these letters reference is made to the cucumber-odor, as having been observed at Boston, Springfield, Holyoke, Mass., and at Poughkeepsie, N. Y. In the majority of cases the odor was connected with the increase of temperature in the beginning of summer, and continued only for a week or two. In other cases it began in the autumn, and continued into the winter or early spring. The supply of the cities named is derived from ponds, lakes, and rivers; but it is interesting to note that there is no report of any fish-like odor in the water of any city supplied from the Great Lakes. These odors are extremely volatile; boiling readily expels them, and they gradually escape when the water is exposed to the air.
Hemlock Lake, in Livingston County, New York, situated thirty miles south of the city of Rochester, is about seven miles in length, and has an elevation of about 400 feet above the level of the city. The water is taken from the northern end of the lake, and conveyed in a large conduit-pipe a distance of nearly twenty miles to the main storage-reservoir in the town of West Rush; from here it is carried to the reservoir at Mount Hope, whence it is distributed to all parts of the city. "The difference of elevation between the storage and the distributing reservoirs is 115 feet, and renders it possible, except in winter, to throw up the whole volume of water, as it enters the Mount Hope Reservoir, to a height of about eighty feet, thus producing a magnificent fountain, which is visible from all elevated points throughout the city. By this means the whole body of water is thoroughly aërated before it enters the distributing mains."
The investigation, which consisted of chemical analysis and microscopical examination, began December 14th. Samples of water were taken from Hemlock Lake, from the chief storage-reservoir, and from the city mains. The analysis, which was conducted with great care, indicated remarkable purity of the water. It should, however, be noted that earlier experiments might have shown a different result. The microscopical investigation was also conducted with scrupulous care, and with such precautions as to preclude the possibility of the escape of any important organism. The total quantity of foreign matter obtained was in each case surprisingly small—"a thousand gallons of water yielding not more than one or two grains of residue, a large proportion of which consisted of minute particles of clay and sand." The facts obtained regarding the fish-like odor were of curious interest. The samples of water taken from the lake and from the reservoirs were found to be entirely free from unpleasant odor, while the fish-like peculiarity was plainly perceptible in the water drawn from the main just before it entered the Mount Hope Reservoir. The odor increased in intensity the farther the water flowed through these mains; so that, in the northern portions of the city, it was very offensive. It is noteworthy that all the water which reached the city had passed through not less than four wire screens with meshes a quarter of an inch in diameter, and in no case had a service-pipe been known to be obstructed by any portion of the body of a fish. "In filtering many thousands of gallons of water, at different times, and under such conditions as to arrest multitudes of the minutest organisms, not the smallest fragment of a bone, or fin, or scale, of a fish—parts which would longest resist decomposition, and float away in the water—has ever been detected."
In answer to the question, "What cause, then, can be assigned for this most peculiar odor?" Prof. Lattimore asserts that it must be due to the decomposition of some form of fresh-water algæ. He draws his conclusions partly from the investigations of others, and partly from his own observation and experiment. After the disappearance of the odor from the water, he observed that microscopic algae, which had collected on the filters through which water had been flowing for twenty-four hours, exhaled an odor strikingly like that given off by a blade of early spring grass, when crushed by the fingers. A minute quantity of these algæ put into distilled water, and kept covered for a few hours, revealed an odor which was distinctly recognized as that which had recently affected the water from the lake.
This experiment, with others pointing in the same direction, leads to the conclusion that the fish-like odor must be due to some obscure condition of the algæ—most likely to their decay and decomposition. Concerning the possibility of communicating so powerful an odor to a vast quantity of water by means of an almost infinitesimal amount of algæ, the author says: "That this odorous material was extremely volatile, was obvious. It soon vanished from water left at repose in the open air. Heat expelled it still more rapidly. It was for this reason that no trace of it could be perceived in the open reservoirs where it could escape as rapidly as it was generated, while in the closed conduit from the West Rush Reservoir to the Mount Hope Reservoir, and in the street mains of the city, it was prevented from escaping except when a faucet was opened. Again, in its extreme volatility we have the clearest explanation of the fact that so minute a quantity of odorous material could infect so large a quantity of water. A single flower will instantly communicate its perfume to every particle of the air in a large room. A grain of musk, or a shred of scorched animal tissue, will taint a vast volume of air with no loss of substance appreciable to the most delicate balance."
Regarding the public health, there is no evidence furnished that warrants even a suspicion of any deleterious effect, and this is strictly in accordance with what would be expected if the above explanation is correct.
To the question, "Can any measures be taken to prevent a recurrence of this trouble?" the following answer is made: "It is useless to attempt a reply until we come to understand the causes and conditions precedent to such results. This knowledge can evidently be acquired only by long and patient observation, if obtained at all; and, if obtained at last, it might be only like our knowledge of the laws of meteorology, which indeed enables us to predict the coming changes of the weather with great certainty, but which confers on us no power whatever to control it. On the other hand, it is at least conceivable that, if we understood the life-history of these offensive algæ, and the conditions favorable or unfavorable to their growth and multiplication, we might possibly be able to prevent or favor their growth, or to hasten or retard their destruction in such manner as to prevent the recurrence of the trouble."
- Abstract of a Report to the Executive Board of the City of Rochester, N.Y., on the Recent Peculiar Condition of the Hemlock Lake Water-Supply. By S. A. Lattimore Ph.D., LL.D., Professor of Chemistry in the University of Rochester.