Abstract
This article presents a case study of corrosion control in the Pacific Northwest. Though clean, much of the water in the Pacific Northwest is soft, has low mineral content, and is aggressive (corrosive) to metallic piping materials. Because of customer complaints about rusty water in areas served by unlined cast iron pipe, as well as concerns about lead leaching, the treatment department staff began investigating corrective actions that would provide long‐term or permanent solutions to corrosion in the distribution system. Polyphosphate addition reduced corrosion and suppressed lead and copper leaching. This article briefly describes the process of getting polyphosphate treatment approved by the state regulators and the city council, then goes into some detail to describe the two‐phase corrosion control operation. Phase one involved cleaning and flushing the mains and conducting a public information program to explain polyphosphates and to warn customers that the water would appear dirtier for the first three months of the program, while the cleaning and flushing was conducted. During flushing, a fairly large dose of polyphosphate was fed to soften the scale and corrosion so it could be flushed out. In the second phase, polyphosphate feed was reduced, the frequency of line flushing decreased, and monitoring of the behavior of the chemicals and of corrosion indicators began. Corrosion coupon loops were installed at the water treatment plants prior to phosphate feed points. A table shows the difference in lead levels before and after the corrosion control program; customer complaints before and after; and the cost of clean up and maintenance, as well as chemical costs. A second table shows the effects of various corrosion control treatments in regard to the lead rule.
Published Version
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