A portion of the water supply of Troy, N. Y., is obtained from the Tomhannock Reservoir, located about ten miles northeast of the city. The reservoir, formed by the construction of a dam, has an area of 1,085 acres, an average depth of 22.4 feet, and a capacity of 12,310,000,000 gallons. The area flooded consisted of about one-seventh wood lands, while the remainder was lands under cultivation. All buildings, trees and brush were removed from the area which was flooded, as were also some 22,000 cubic yards of muck and decaying vegetable matter. The drainage area is 07.3 square miles, about 15 per cent of which is wood lands. There is a population of about 35 per square mile on the drainage area. The reservoir is about 0 miles long, and has an average width of three-quarters of a mile. The first water was delivered from this reservoir on May 21, 1906. The algea first appeared in this water during January, 1908, at which time the reservoir was covered with ice. At that time the following organisms were present : Dinobryon, Crenothrix, Chalamydomonas, Cosmarium, Navicula, Synedra, Asterionella, Nitzschia, Anurea, Surilella and Stabablast.

Several of the above mentioned forms were present in sufficient numbers to cause trouble due to odor and taste. These forms of algea being present during the entire winter and up to the time the ice left the reservoir, showed that the low temperature of the water did not kill them. During the summer of 1908 algea again in larger numbers began to develop in Jhe reservoir, the following additional forms being present : Crenothrix, Asterionella, Navicula, Staurastrum, Cymbclla, Nitzschia, Anabaena, Closterium, Pleurosignta, Chalamydomonas, Melosira, Raphidium, Cosmarium, Fragilaria, and Synedra. It is to be noted that most of the forms present at this time were different from the ones that caused the trouble during the previous winter. An examination on October 15, 1908, showed that the Melosira were incerasing, the numerous frosts not having killed this organism. Owing to this condition, arrangements were made to treat the water with copper sulphate. The treatment was started on November 11, but because of climatic conditions was not completed until November 25, 1908. The temperature of the water at the time of treatment was 35° F. Because of the chemical composition and the low temperature of the water the copper sulphate was applied at the rate of 1 part of copper sulphate to 2,180,000 parts of water ; this is equal to about 1 pound of copper suluphate to 282,000 gallons of water. The cost of this treatment was as follows:

Owing to the extreme drouth of the summer the reservoir contained only about 5,000,000,000 gallons of water.

From the above it is seen that the cost of the treatment was about 32.5 cents per million gallons. In applying this treatment, 2 power boats, 2 row boats, and 7 men were employed. The treatment was a success, and no trouble due to odor and taste was experienced during the winter. Commencing with July 23, 190t>, bi-weekly microscopical examinations of the water were made, the object being to determine the variety and number of organisms present, and so be ready to treat the water in the reservoir when the organisms became present in large numbers and before they began to decompose, and thus avoid the disagreeable odor and taste which oc cur at such times.

The following organisms were present at some time during these examinations: Asterionella. Crenothrix, Nitzschia. Cymbella, Melosira. Synedra, Navicula, Closterium, ScenedismUs, Urog lena. Pcdiastrum. Raphidium, Anabaena, Coelas trum. Staurastrum, Ceratium, Microcystic, Pleu rosigma, Pandorina, Chaerophora. Cyclops, Cocconeia and Cosmarium.

It was very interesting to note the great variety of organisms present, and also, at different times, the almost complete change in type. These changes no doubt were due to the currents in the reservoir, causing the water to flow from different locations. About the latter part of August, 1909, the results of examinations indicated that the time had arrived to again treat the water in the reservoir. At this time the temperature of the water was 65° F. The work was started on Sept. 7, and completed on Sept. 20, during which time 10,500,000,000 gallons of water received treatment. The cost of this treatment was as follows:

* Paper read at a meeting of the New fork As soelatlon of Private Water Companies. December 11. 1909.

The total cost per million gallons treated was 14.9 cents. Two power boats, six row boats, and nine men were employed in applying the copper sulphate. At the time of treatment the water was two feet below the overflow. It is to be regretted that the reservoir did not contain its full capacity, as it would have then been possible to treat parts which have never yet been reached. Very heavy growths, however, were found in portions of the reservoir. In some locations, measurements showed the growths to be over one inch in thickness. Owing to this extreme condition it was necessary to apply the dose as strong as 1 part of copper sulphate to 1.000.000 parts of water (1 pound of copper sulphate to 120,000 gallons of water )in these places.

In other portions of the reservoir the dose was much weaker. The average dose for the entire reservoir was 1 part of copper sulphate to 3,472,000 parts of water (1 pound copper sulphate to about 420,000 gallons of water). In the section of the reservoir where the growth required strong treatment fish were killed. They usually began to die about six hours after the treatment has been applied, and continued to do so for about five days. At least twenty tons of dead fish, consisting of carp, suckers and a few bull heads, were removed from these sections, no bass or other game fish were killed. The carp weighed from two to fiften pounds each; the suckers were from six to eight inches long. At times the death of the fish was so rapid that it was impossible to remove the bodies at once, yet a large force of men was employed and every effort madeto have them all removed at the close of each day. Fourteen men were employed in removing the fish, and it is to be noted that it cost more to do this than it did to apply the copper sulphate. Carp and suckers are very undesirable fish in reservoirs where there is any mud on the bottom, as they work continually therein, thereby causing the water to become turbid. Because of the stumps in the reservoir it was imposibsle to remove the undesirable fish with nets. This treatment of the reservoir was successful, and the water at the present time is free from odor and taste.

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