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Disinfection Byproducts Federal Advisory Committee predicted that the use of chloramines could increase to as much as 65% of surface water systems (U.S. EPA M/DBP FACA Support Document, 2000). For non-ICR systems serving less than 10,000 people, it is estimated that approximately 50% of utilities will shift from free chlorine to chloramines to reduce DBP levels below the Stage I MCLS (U.S. EPA M/DBP FACA Support Document, 2000). 2.0 Description of Potential Water Quality Problems Nitrification can have the adverse impacts of increasing nitrite and nitrate levels, reducing alkalinity, pH, dissolved oxygen, and chloramine residuals, and promoting bacterial regrowth (Wilczak et al. 1996). Table 1 provides a summary of water quality problems associated with nitrification. Chemical Issues Biological Issues Disinfectant Depletion HPC Increase Nitrite/Nitrate Formation Ammonia Oxidizing Bacteria (AOB) Increase Dissolved Oxygen Depletion Nitrite Oxidizing Bacteria (NOB) Increase Reduction in pH and Alkalinity DBP Formation due to Mitigation Techniques Various potential health impacts have been associated with issues identified in Table 1. The Chemical Health Effects Tables (U.S. Environmental Protection Agency, 2002a) provides a summary of potential adverse health effects from high/long-term exposure to hazardous chemicals in drinking water. The Microbial Health Effects Tables (U.S. Environmental Protection Agency, 2002b) provides a summary of potential health effects from exposure to waterborne pathogens. While nitrification can degrade water quality, the formation of nitrite/nitrate and DBP formation during nitrification mitigation are the only water quality issue identified in the literature with the potential to impact public health directly. Other issues listed in Table 1 either are already regulated under provisions of the Safe Drinking Water Act, or were not identified within existing literature as posing direct public health impacts. However, more research may be needed to better understand interactions between these issues. For example, reductions in pH and alkalinity can be a symptom of nitrification, as shown by hydrogen ion formation in equations (1) and (2). Although reductions in pH and alkalinity may not pose a direct public health threat, such reductions could theoretically lead to a violation of the USEPA Lead and Copper Rule (1991) either through failure to maintain designated optimal water quality parameters, or possibly through an action level exceedence at the tap. In 1997, the City of Willmar, Minnesota conducted a study to determine the causes of copper corrosion within household plumbing systems. Preliminary indications were that both nitrification and copper corrosion proceeded simultaneously during water distribution, so that there might be some linkage between the two phenomena within specific households (Murphy et al., 1997). System -wide Lead and Copper Rule violations due to nitrification were not cited in the literature. Prepared by AWWA with assistance from Economic and Engineering Services, Inc. 4