Materials Performance

JUN 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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O FEATURE ARTICLE Corrosion Caused Lead-Tainted Water in Flint, Michigan Kathy Riggs Larsen, Editor Over the past year, overall awareness of the issue of lead contamination of potable water has increased due to the high levels of lead detected in drinking water from homes in Flint, Michigan in 2015. The cause of lead leaching into the water in Flint was corrosion of the water distribution system's service pipes and solder. This was determined by a team of research scientists and students from Virginia Poly- technic Institute and State University (Virginia Tech) (Blacksburg, Virginia) that worked with Flint resi- dents to study the water and establish the cause of the widespread contamination. In a water distribution system, corrosion of pipes and solder causes the dissolution of these materials. The metals then leach into the water supply, which causes lead and copper concentrations in the water to increase. According to the U.S. Environmental Protection Agency (EPA), it was common practice up through the early 1900s to use lead pipes for interior plumb- ing and the service connections that join residences to public water supplies. Homes built before 1986 are more likely to have lead pipes, fixtures, and solder that can leach significant amounts of lead into the tap water, especially hot water. Although copper pipes have replaced lead pipes in most residential plumbing, the use of lead solder with copper pipes had been widespread and was regarded as the major cause of lead contamination in U.S. households in the 1990s. The amount of lead that contaminates drink- ing water is influenced by several factors, such as the corrosivity of the water, the amount of lead it con- tacts, the amount of wear in the pipes, the length of time that the water stays in the pipes, and the pres- ence of protective scales or film inside plumbing components. Water's corrosivity is determined by characteristics such as low pH (acidity), dissolved oxygen, and low mineral content. Because lead contamination of drinking water often results from corrosion of the plumbing materi- als belonging to water system customers, the EPA established a treatment technique regulation for lead known as the Lead and Copper Rule (LCR). This rule requires water treatment facilities to control the cor- rosivity of drinking water and make it less corrosive to the materials it contacts on its way to consumers' faucets. Adjusting alkalinity and pH is one technique many water distribution systems use for corrosion control. Phosphate-based corrosion inhibitors also have been widely used to control lead and copper release. Phosphate-based corrosion inhibitors are chemicals that have orthophosphate in their formu- lation. Orthophosphate bonds with lead and copper ions to form a protective coating that has a strong tendency to stay in solid form and not dissolve in water. 1 A Change in Flint's Water Source The City of Flint had signed a long-term water supply contract with the Detroit Water and Sewerage Department (DWSD) and utilized this water source for almost 50 years. The DWSD water supply had been treated for corrosion control with orthophos- phate for over 20 years and was on a maintenance dose of orthophosphate since its corrosion control treatment was fully optimized. Although Flint had a water treatment plant, it served as an emergency backup; it was upgraded periodically to keep it ready for use and was put into operation four times a year to maintain its readiness. In April 2014, because of annual rate increases from the DWSD, the Flint City Council voted to join the Karegnondi Water Authority (KWA), which would be developing a raw water supply pipeline from Lake Huron. The water supply contract with DWSD was subsequently terminated, and the Flint water 26 JUNE 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 6

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