PROTECTING NEW YORK’S WATER SUPPLY
All of the Greater City’s Water Treated with Liquid Chlorine—Practically All Surface Water—Chlorine Recognized as the Cheapest Form of Municipal Health Insurance—Method of Application
IF any member of the New England Water Works Association in attendance at its convention held ten years ago in New York City had, in addressing the meeting, indicated that in 1919 nearly every public water supply in the United States would be chemically sterilized, very likely that individual would have been judged over confident and optimistic to the point of mental deficiency. Nevertheless, today, nearly three thousand public water supplies are treated with liquid chlorine and the development of the process has far exceeded the hopes of the most enthusiastic believer in the chemical disinfection of potable water.
New York City is the largest user of liquid chlorine in the purification of water supplies, and has been most consistent in the installation of adequate equipment to chlorinate every supply and each additional source of water as fast as developed.
The water supply of Greater New York is practically all surface water. The recently completed Catskill aqueduct system, brings to the city a supply of water obtained from Esopus Creek, stored in the Ashokan Reservoir. The Croton Aqueduct carries to the city the surface supply obtained from the Croton Water Shed and stored in Croton Lake and contiguous reservoirs and ponds. Both make available the 650,000,000 gallons of water that are normally consumed each day in Greater New York. A thorough system of water shed supervision, inspection and patrol has long been in service, protecting Greater New York’s water supply but with the development of adequate means of chemically disinfecting drinking water those responsibly in charge of the water supply of the city of New York concluded that the welfare of the city demanded that every possible safeguard be used to insure water of maximum purity reaching the consumer. Believing that the chlorination of water is the cheapest form of municipal insurance that a city can obtain it was determined that all surface water supplies should be chlorinated. A calcium hypochlorite treatment plant was installed at Dunwoodie to chlorinate the supply obtained from the Croton Shed, this was subsequently replaced by liquid chlorine control apparatus.
Chlorine Control Apparatus
In 1914, determined to keep abreast of developments in the field of chlorination, the Department of Water Supply conducted exhaustive tests on all available types of chlorine control apparatus to determine the most reliable type and standardize upon it. As a result of this the Wallace & Tiernan Chlorine Control Apparatus was selected and has since been used as the standard equipment for all of the chlorinating plants of the Greater New York water supply.
The first units of equipment were installed on some of the surface supplies obtained in Long Island, the equipments being placed in service at the Smith’s Pond, Watts’ Pond and Millburn Pumping Stations and subsequently at the Bayside Pumping Station and at West New Brighton, Staten Island. All of these equipments are still in service and are held in reserve, since the availability of the Catskill supply made it unnecessary to continually draw on the Long Island surface supplies. For the Smith’s Pond, Watts’ Pond and Milburn Pumping Stations, manually controlled direct feed chlorinators were installed, applying the dry gas to the water, just prior to pumping. At Bayside and West New Brighton, manually controlled solution feed chlorinators were installed.
Largest Chlorinating Installation in the World
In April, 1916, the largest installation of chlorinating equipment in the world was placed in service at Dunwoodie, N. Y., to treat the 340,000,000 gallons of water passing through the New and Old Croton aqueducts each twenty-four hours. This installation contained many new developments in chlorine control and its application for the sterilization of water supplies, both on account of the physical conditions encountered and the large volume of gas demanded.
However, the standardized equipment that had been adopted by the City of New York met all requirements and the nine units of chlorine control equipment, each having a capacity of three-hundred and twenty-five pounds of chlorine per twenty-four hours, were installed in a small portion of the old hypochlorite house at Dunwoodie.
Method of Application
The chlorine is applied as a dry gas directly to the water passing through the aqueduct, by means of suitably constructed grids of chlorine diffusors, each diffusor being connected by silver tubing to central feeding lines. Nearly four years of absolutely continuous operation of these equipments with an extremely low maintenance and up-keep cost, has justified the designs of the manufacturers and their approval by the Department of Water Supply.
That portion of the Croton supply flowing from the Kisco River is treated with chlorine before it enters into Croton Lake on account of the high bacterial content of the river water and the increased possibility of pollution from the district through which the river flows. Although the chlorination of water flowing from an open stream presented problems not previously encountered by the Department of Water Supply, here again the standardized equipment was applicable and five units of manual control direct feed apparatus were installed in the special chlorinating house built on the river bank at Mount Kisco.
At this installation, the chlorination is not directly applied to all of the water flowing in the stream but is introduced to a portion of the water taken from the main stream flow, and subsequently re-entering the stream, carrving with it the chlorine requirement for proper disinfection of the entire flow.
All of Catskill Supply Chlorinated
All of the Catskill supply is chlorinated as the water enters the aqueduct, running from the Kensico reservoir to the city, the equipment being installed in a gate chamber at Kensico, N. Y. Here, also, the standardized control units were applicable, but the tremendous velocity of 500,000,000 gallons of water entering the aqueduct necessitated the development of special devices to introduce the chlorine into the water.
Injectors made of silver and vulcanite were used, and were installed in the injector gallery, just above the aqueduct. All these units have been in absolutely continuous and satisfactory operation without any repairs having to be made upon them whatsoever, for a period of over two years. It is worthy of note that the standardized apparatus was applicable to all of the problems encountered in the chlorination of the Greater New York water supply. The continuous operation and absence of difficulties coupled with low maintenance costs testifies to the merit of the equipment. The remarkably low typhoid death rate of 3.3 per 100,000 per year testifies to the adequacy of the protection given.