February 27, 1913: Engineering News article. Chlorinating Plants, Croton Water Supply. “Synopsis—Operating results of a temporary plant, which treated with hypochlorite of lime more than 100 billion gallons of Croton water for New York City in 1912, are given. A permanent hypochlorite or chlorinating plant, to treat the flow through both the old and the new Croton aqueducts, is described and fully illustrated. Brief descriptions are given of four other chlorination plants in the Croton drainage area: Three to treat the waters of tributaries of the Croton before it reaches the main supply and one to treat another tributary and a part of the sewage of the village of Brewster, N. Y.”
In June, 1910, I. M. de Varona, chief engineer of the Department of Water Supply, Gas and Electricity of the City of New York, made trials of hypochlorite treatment in connection with the Croton water-supply. The results were so satisfactory that its use has been extended until the city now maintains five of these plants: one on the New Aqueduct at Pocantico, treating the entire supply from the Croton, and the other four upon various tributaries of the reservoirs.
The continuous treatment of the flow of the New Croton Aqueduct was commenced in June, 1911, the plant being located at Shaft No. 9, north of Tarrytown, N. Y., known as the Pocantico plant. It consists of a rough frame building which houses two cement-lined cypress tanks, 12 ft. in diameter and 6 ft. in height, and a constant-level feeding tank with adjustable orifice discharging through a manhole into the crown of the aqueduct. Within the aqueduct, there is suspended a wooden grid to secure a proper mixture of the chlorine solution and the flowing water. The operating floor is just above the solution tanks and in it are two screened mixing pits.
In operation, a drum of lime, weighing about 800 lb., is rolled into position over a pit and the contents washed out into the pit by a hose stream under pressure. Enough ‘bleach’ is dissolved to treat the aqueduct flow for 12 hours. The tank is then filled with water and stirred to assure the thorough absorption of the chlorine. Four men operate the plant, two on the clay shift, making solution, and one on each of the night shifts, maintaining a constant, uniform flow of the solution.
Experience has shown the desirable amount of chlorine to be between 0.40 and 0.65 p.p.m. (parts per million). The lower amount is used in warm weather and when Croton Lake is near the high water line. The amount is gradually increased as the storage in Croton Lake drops or the temperature of the water approaches freezing. The amount of ‘bleach’ to be used daily is determined from a chart (Fig. 1), which shows that the daily amount of chemical is about 4000 lb. Where so much chemical is used, the chart shows the economy resulting from varying the charge of ‘bleach’ in accordance with the amount of its available chlorine, as determined by laboratory analysis.”
Reference: Coffin, T.D.L. 1913. “Chlorinating Plants, Croton Water Supply.” Engineering News. 69:9(February 27, 1913): 419-21.
Commentary: New York City began testing chloride of lime to disinfect the Croton water supply shortly after the findings of the special master in the second Jersey City trial which has been described at length in The Chlorine Revolution: Water Disinfection and the Fight to Save Lives.