Lead and copper in municipal water systems present a major health hazard in addition to the infrastructure loss associated with corrosion releasing them into the distribution system. Soluble lead and copper became a legal as well as economic concern with the implementation of the Lead and Copper rule in the United States in 1991 and its subsequent expansion. Similar regulations where implemented in Canada during the same time period. The regulations set action limits for the metals at 15 µg/L for Pb and 1.3 mg/L for Cu.
Lead and copper in municipal systems can result from soluble lead in copper in the water source, corrosion releasing soluble ions into the water, and the dissolution of corrosion product and other lead and/or copper deposits. The dissolution process can be increased, or limited, by changes in water chemistry due to seasonal variations, changing water sources, or changes in treatment. In some cases, treatment directed towards minimizing corrosion as a source of lead and copper, can actually increase the solubility of the ions.
This paper describes a two fold approach to computer modeling of lead and copper corrosion, and the maximum solubility of lead and copper in the municipal water. The methods outlined can be used to:
Model lead and copper corrosion in a distribution system.
Model the maximum solubility of lead and copper as an indicator of the waters ability to dissolve deposits, and transport soluble Pb and Cu ions through the system.
Predict the impact of changing water sources upon lead and copper levels in the system.
Predict the impact of treatments, including pH adjustment upon lead and copper in the system.
Examples are provided based upon a recent, well publicized, water change that resulted in high lead levels in a municipal water system. The method outlined was used to evaluate a municipal water, and compare traditional indices, maximum lead and copper solubility, and predicted corrosion rates, to the river water that replaced it.