AWWA WQTC65709

Lead is a toxic heavy metal and the adverse effects of lead consumption are a public health concern. Water leaving treatment plants has very low concentrations of lead. However, internal corrosion of lead-containing pipe, fittings, and solder in water distribution systems is currently the most significant source of lead to drinking water. While new construction does not use lead pipe, many older buildings retain the original lead service lines and internal plumbing. Concern for lead concentrations in water distribution systems motivated the U.S. Environmental Protection Agency (USEPA) to pass the Lead and Copper Rule (LCR) in 1991. The LCR set the lead action level to 0.015 mg/L. The understanding of the relationships between water chemistry and the solubility of lead-containing minerals has increased since the passage of the LCR. However, the recent observations of extremely high lead levels in Washington D.C. tap water highlight the need for continuing research. Lead concentrations in drinking water are affected by chemical reactions that occur within the water distribution system. Previous studies have investigated the equilibrium solubility of lead corrosion products. This project focuses on dissolution rates. Knowledge of lead release rates are useful for evaluating potential effects of treatment process changes on water quality in the distribution system. The dissolution rates of the important lead corrosion product, hydrocerussite (Pb₃(CO₃)₂(OH)₂), will be determined as a function of pH, dissolved inorganic carbon, orthophosphate, and the presence of chloramines. The lead corrosion products will be characterized with respect to surface area, molecular structure, morphology, and mineralogy. The dissolution rates of these lead corrosion products will be quantitatively determined in completely-mixed continuous-flow reactors. The experimentally measured dissolution rates will be used to generate a model for dissolution rates as a function of water chemistry. This model will then be used to evaluate the dissolution of pipe scales excavated from a water distribution system. Includes 19 references, tables, figures.