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THE SIGNIFICANCE OF "STAGNATION CURVES" FOR LEAD AND COPPER, AND WATER QUALITY FACTORS AFFECTING THEM
Citation:
Lytle*, D A. AND M R. Schock*. THE SIGNIFICANCE OF "STAGNATION CURVES" FOR LEAD AND COPPER, AND WATER QUALITY FACTORS AFFECTING THEM. Presented at 118th Annual Conference of the New England Water Works Association, Burlington, VT, 9/19-22/99.
Description:
"Stagnation curves" are the response of metal levels, particularly lead and copper, to time under conditions of no water flow. Research on lead pipe in the early 1980's in the United States, Germany, and in the United Kingdom suggested that they were characterized by rapid increases over the first few hours, followed by a "leveling-off" after approximately 8-12 hours. For lead plumbing systems, this was essentially the solubility limit for lead. Usually, it has been implicitly assumed that copper behaves similarly, forming the basis for the sampling suggestion of 6 to 16 hours under the Lead and Copper Rule. Recently, investigations with copper in different water chemistries has shown a strong relationship of the metal level to the remaining concentration of oxidant (dissolved oxygen, free chlorine). Research by other investigators have shown similar relationships for iron release, and the potential production of "red water". The resulting unexpected stagnation curves are much more complex than those produced through control by simple diffusion mechanisms. Thus, a variety of serious interpretation errors on the potential for corrosion and the effectiveness of corrision control measures are possible with apparently simple and straightforward field or pipe rig data. Human exposure estimates can also be seriously biased, both high or low. This presentation uses field and laboratory data produced by our own research and other investigators to examine what is currently known about the factors influencing the shapes of the stagnation curves, and the implications for field and laboratory investigations of corrosion control for lead, copper and iron.