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The United States enjoys one of the world's highest standards of drinking water, but Environmental Protection Agency (EPA) water researchers are always alert to new risks of contamination, whether at the point of treatment or in the distribution systems that carry finished water to the consumer. One example is ongoing National Risk Management Research Laboratory (NRMRL) research into possible impacts on water distribution systems following changes in disinfection practices. About one-third of major U.S. water companies are changing from traditional chlorine treatment to chloramine to guard against harmful disinfection by-products (DBPs) resulting from the reaction of chlorine with organic matter in the water. Chloramine, a combination of chlorine and ammonia, is a weaker oxidizer than chlorine and thus less likely to create harmful DBPs. While the change to chloramine enhances some aspects of water quality, it may also generate electrochemical reactions capable of dissolving lead from the mineral lining of water pipes.

Figure 1: Recirculating Loop Distribution System Simulator

When cities such as Washington, D.C. and Greenville, North Carolina, began experiencing unusually high levels of lead in drinking water after switching to chloramines, NRMRL water researchers responded with collaborative monitoring, corrosion control studies, and pipe-scale analyses that are leading to new findings about the transport of lead in water systems. This new EPA research has shown that lead coatings in pipes tend to be stable and insoluble in the presence of highly oxidizing (chlorine-treated) water. But with the shift to chloramines, the oxidizing power of the water is lowered, resulting in the potential dissolution of lead from the thin shell of mineral scales lining pipe walls. Although some outside studies have corroborated the NRMRL scale-dissolution findings, pipe-scale chemistry is complex, and many other potential mechanisms exist for pipe-scale destabilization. Further corrosion studies are needed to aid in understanding the role of these mechanisms across the diverse array of water chemistries and treatment histories of U.S. water systems.

Figure 2: Online Water Quality Monitoring Station

Currently, NRMRL researchers are collaborating with researchers in several cities who are doing anticipatory studies or monitoring before-and-after treatment changes. Work is also being done with the U.S. Geological Survey (for elemental analysis of the solids); Pegasus Environmental Services (for in-house lab assistance); and the Department of Energy (for use of the Advanced Photon Source at Argonne National Laboratory in determining the speciation of lead solid phases). The results of these combined efforts will reinforce the EPA mission of ensuring safe drinking water-from the treatment source right to the consumer tap.

For more information, visit the Corrosion, Scaling, and Metal Mobility Research website at http://www.epa.gov/nrmrl/wswrd/cr/index.html.