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The Impact of Water Quality, Corrosion Inhibitors and Plumbing Age on Copper Release in Distribution Systems
Citation:
LYTLE, D. A. The Impact of Water Quality, Corrosion Inhibitors and Plumbing Age on Copper Release in Distribution Systems. Presented at 2009 Illinois Section AWWA Meeting, Springfield, IL, March 16 - 19, 2009.
Impact/Purpose:
The objective of this presentation is to discuss the effect of water chemistry on the solubility and release of copper into water. Of particular interest to the State of Illinois will be the discussion on role of plumbing age, and alkalinity, pH, and phosphates on copper corrosion and release. The project objectives will be met by presenting the latest U.S. EPA research findings from bench-, pilot- and full-scale studies.
Description:
The U.S. Environmental Protection Agency promulgated the Lead and Copper Rule (LCR) in 1991, which established a copper action level of 1.3 mg/L in the consumers’ tap water. As a result, researchers have examined the effects of water chemistry on the solubility of copper to establish best approaches for reducing copper levels. Since the implementation of the LCR, a great deal of research has been conducted on copper corrosion and the leaching of copper from materials in drinking water distribution systems. Despite new developments, however, a number of important gaps still exist regarding copper corrosion and release. The objective of this presentation is to discuss the effect of water chemistry on the solubility and release of copper into water. Of particular interest to the State of Illinois will be the discussion on role of plumbing age, and alkalinity, pH, and phosphates on copper corrosion and release. The project objectives will be met by presenting the latest U.S. EPA research findings from bench-, pilot- and full-scale studies. Perhaps one of the most recent research finding is the impact of age on copper release to drinking waters. Copper minerals “age”, and this aging process has been conceptually described in the “cupric hydroxide model”. The model is based on U.S. EPA studies and field observations, and essentially predicts that the solubility of Cu(II) in new copper and brass plumbing systems is controlled by relatively soluble cupric hydroxide. Over time, however, this cupric hydroxide phase transforms into less soluble minerals, malachite or tenorite depending on water chemistry. From a practical standpoint, the model predicts worst copper levels to be in newer homes rather than targeted LCR sampling locations (e.g., homes built before the 1980’s having lead service lines). The rate of aging and the solubility of copper are controlled by water chemistry. Of particular importance is the pH and dissolved inorganic carbon concentration (DIC) (i.e., alkalinity) of the water. Alkalinity is commonly elevated in many Illinois groundwater’s and likely the main cause of high copper levels in homes across the State. The difficulty in addressing such cases is DIC is to remove and high DIC waters are well buffered and susceptible to calcium deposition. Orthophosphate is perhaps the most reasonable solution to reducing copper levels in high DIC waters. The relationships between plumbing age pH, DIC, orthophosphate and copper concentration will be discussed from a theoretical and practical standpoint using study results.
