New York City has one of the most fascinating water systems in the world. Raw water is supplied from a network of 19 reservoirs and three controlled lakes in a 5,120 square kilometer watershed that extends 200 kilometers north and west of the City. About 90% of the supply, roughly 3.4 billion liters per day, comes from the Catskill/Delaware System, which consists of six source water and two balancing reservoirs. The only treatment provided is disinfection with free chlorine, corrosion control, and fluoridation – this is the largest unfiltered supply in the United States. While the quality of the raw water is extremely high, there are concerns about meeting the more stringent requirements of the United States Environmental Protection Agency's Stage 2 Disinfection Byproduct Regulations for haloacetic acids (HAAs). A comprehensive study was conducted by the New York City Department of Environmental Protection to evaluate a number of potential NOM/DBP control options including filtration, magnetic ion exchange resin treatment, converting to chloramines, and modifying reservoir operations. The purpose of this paper is to present the results of modifying reservoir operations with the goal of minimizing HAA levels in the City's water supply.

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