Pipe loop demonstration study of corrosion control alternatives at a pH of 10

The Federal Safe Drinking Water Act (SDWA) under the Lead and Copper Rule (LCR) requires many water supply utilities to reevaluate their current method of corrosion control and has resulted in the implementation of numerous capital improvements and/or changes in water treatment plant operations. The Providence Water Supply Board (PWSB) serves more than 600,000 people and maintains a pH of 10 through the treatment plant and water distribution system. Maintaining a pH of 10 results in a calcium carbonate precipitation potential (CCPP) of 5 to 12 mg/l expressed as calcium carbonate. Theoretically, a positive CCPP will result in the precipitation of calcium carbonate which maintains a thin protective film along the interior walls of water distribution pipe and helps minimize lead and copper solubility. Monitoring results indicated that lead levels were close to maximum allowable limits. The application of a pipe loop demonstration study provided information on alternative treatment methodologies to minimize lead solubility while maintaining a pH close to 10.0. Sodium silicate inhibition and dissolved inorganic carbonate (DIC) adjustment were two treatment methodologies which resulted in reducing lead levels by 50 percent.