Planning a Regional Conversion to Chloramines

Authors:

  • Jeff Cruickshank PE - Hazen and Sawyer

The City of Greensboro, NC, recently switched the residual disinfectant in its water distribution system from free chlorine to chloramines. This conversion was part of the city’s compliance strategy for the Stage 2 Disinfectants and Disinfection Byproducts Rule.

Greensboro’s distribution system supplies nearly 300,000 people with water from several sources, including the city’s two treatment plants and purchased water from the City of Reidsville, the City of Burlington, and the Piedmont Triad Regional Water Authority. The water treatment plants that supply Greensboro’s purchased water also provide water to several other systems, including Elon, Gibsonville, High Point, Jamestown and Archdale, NC. All these systems converted to chloramines at the same time to avoid water quality problems associated with mixing residual disinfectants.

This presentation describes the planning and coordination that resulted in a successful disinfectant conversion. The timeline for construction of chemical feed systems at the various water treatment plants is reviewed, as well as the extensive public notification program.

The presentation also shows how hydraulic models identified Greensboro’s mixing zones that receive water from more than one source. Water quality modeling animated the disinfectant front that moved through the distributions systems and determined travel times from each water treatment plant to the mixing zones supplied by multiple sources.

This information helped the regional water systems coordinate when to begin adding ammonia so that chloraminated water from each source would arrive at the mixing zones at about the same time. This synchronization minimized mixing of newer chloraminated water with older water disinfected with free chlorine.

The presentation also summarizes lessons learned from the project, including how to plan flushing related to the conversion process.

This presentation may help other utilities plan for conversion to chloramines, especially regional systems with several supply sources.

For more information, please contact the author at jcruickshank@hazenandsawyer.com.

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