The monitoring requirements of the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) become effective in 2012 and 2013 for many water systems. To achieve compliance with the Stage 2 DBPR, water systems are increasingly turning to alternate disinfectants to reduce disinfection byproduct (DBP) formation. However, systems with multiple sources or systems that purchase a portion of their finished water can experience difficulty maintaining a chlorine residual when chlorinated and chloraminated source waters are blended in the distribution system. The reactions that occur when free chlorine and chloramines are blended deplete chlorine residual and can result in biological growth, taste and odor complaints, and violations of the Total Coliform Rule (TCR).rnIn 2010 a Water System in Eastern Pennsylvania violated a primary drinking water standard when distribution system water quality samples showed the presence of total coliform bacteria. Further evaluation of distribution system water quality data resulted in the discovery of widespread very low chlorine residuals in an area of the distribution system where purchased water from an adjacent system utilizing chloramines for secondary disinfection supplements the chlorinated groundwater supply primarily used in the Water System. It was determined that these distribution system water quality issues were a result of chlorine breakpoint reactions caused by the mixing of chloraminated water with water containing free chlorine. After evaluating potential corrective measures, the Water System ultimately decided to apply sodium hypochlorite at the point where the purchased water enters the distribution system to convert the chloramines in the purchased water to free chlorine through breakpoint chemistry.rnThis paper includes an overview of the chloramines to free chlorine conversion project, a general discussion of the conversion of chloramines to free chlorine, a discussion of the application of bench test data to full-scale implementation, and assessment of regulatory compliance impacts.
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