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(NEW YORK, NY – March 16, 2009) – The New York City Stage 2 Disinfectant/Disinfection Rule Compliance Study won the Platinum Award in the American Council of Engineering Companies (NY), the second highest honor in the 2009 Engineering Excellence Awards program.

Following passage of the Stage 2 Disinfectant/Disinfection By-Product (D/DBP) Rule, New York City faced the challenge of ensuring that its water supply system would meet the more stringent standards established for allowable levels of DBPs in drinking water. Like most US water purveyors, NYC utilizes chlorine as its disinfectant – an effective, widely-recognized method. Chlorination, however, can produce cancer-causing byproducts, including trihalomethanes (THMs), haloacetic acids (HAAs), and other potentially-harmful, nitrogenated compounds, such as N-nitrosodimethylamine (NDMA). Since these byproducts can be potentially harmful to consumers when their limits are exceeded on a long-term basis, the Stage 2 D/DBP Rule is a prudent measure for further protecting public health.

The New York City Department of Environmental Protection (NYCDEP) retained the joint venture of Hazen and Sawyer/CDM to perform a comprehensive evaluation of DBP control strategies, including alternative disinfectants such as chloramines (a combination of chlorine and ammonia), implementing various treatment technologies, and optimizing source water withdrawal and distribution system operations. The study encompassed:

• Assessing source and fate of DBPs in the NYC water system, developing an extensive sampling program and computerized THM and HAA formation models.
• Evaluating compliance options for the Stage 2 Rule, including treatment processes and optimization of operations.
• Examining benefits, costs, and potential adverse consequences of switching to chloramination, such as corrosion of distribution system piping and production of NDMA.

New York City has until 2012 to comply with Stage 2 (2014, if capital improvements are needed to do so). Historical water quality data indicate that, with continued use of chlorine, THM limits will likely be met, but compliance may be marginal for HAAs at certain locations within the City’s distribution system. The City needed to ensure the Stage 2 regulations would consistently be met, and wondered whether chloramination – which tends to form fewer disinfection by-products than chlorine – would be a viable alternative to chlorination, assuring the continued high quality of City drinking water.

As the first of its kind to be undertaken for a major water purveyor, the study set an important precedent, with key components including:

• A comprehensive monitoring program, established to characterize naturally-occurring materials and track seasonal and annual variations affecting DBP formation.
• A system-specific, computerized DBP prediction model to aid in investigating various DBP control options.
• An in-depth unintended consequences analysis, investigating the possible adverse outcomes of switching to chloramination.

Upon completion, these complex, interrelated studies determined that optimizing water system operations, with respect to both water supply/reservoir withdrawals and distribution system practices, would be an effective – and cost-conscious – means of controlling DBPs, meeting stricter regulatory requirements, and safeguarding public health.

For more than half a century, Hazen and Sawyer has focused on two things: providing safe drinking water and controlling water pollution. Our range of services encompasses the planning, design, and construction management of water and wastewater-related projects – from clean water treatment, storage, and distribution to wastewater collection and treatment. Since our founding in 1951, we have grown in size to over 740 employees in 25 offices.