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SOLVING COPPER CORROSION PROBLEMS WHILE MAINTAINING LEAD CONTROL IN A HIGH ALKALINITY WATER USING ORTHOPHOSPHATE
Schock*, M R. AND J. C. Fox. SOLVING COPPER CORROSION PROBLEMS WHILE MAINTAINING LEAD CONTROL IN A HIGH ALKALINITY WATER USING ORTHOPHOSPHATE. Presented at AWWA Annual Conference, Washington, DC, 6/17-21/2001.
Lead and Copper Rule sampling in 1992 uncovered high copper levels in many homes in the Indian Hill Water Works, Ohio (IHWW) water system. The 90th percentile copper and lead levels were 1.63 mg/L and 0.012 mg/L, respectively. IHWW supplies water to several suburban communities to the east of Cincinnati. Finished water hardness is approximately 150 mg/L as CaCO3, total alkalinity approximately 250 mg/L as CaCO3, DIC approximately 60-65 mg/C/L, and pH ranges from about 7.1 to 7.5, mostly near 7.3. Final treatment consists of chlorination, fluoridation, and at different times, addition of caustic and/or corrosion inhibitor. Historically, water heater failures and high copper levels resulting in blue water were reported i the 1950's, and caustic addition was used to elevate the pH to as high as 8 at diferent times throughout the next 3 decades. In the late 1980's and early 1990's, zinc orthophosphate treatment was employed, which was mostly successful for lead and inconsistently successful for copper. In 1997 with the 90th percentile still at 1.54 mg/L for copper, the zinc orthophosphate treatment was withdrawn. In 1998, new pilot tests were carried out in collaboration with the Water Supply and Water Resources Division of USEPA in Cincinnati to do some new pilot testing and a more systematic analysis of copper corrosion control chemistry. Tests compared pH adjustment, partial DIC removal through anion-exchange and increasing orthophosphate dosing. The most economical alternative identified was an increased orthophosphate residual of 3 mg/L as PO4. The recommended treatment was implemented beginning in 1999. Lead levels were below 0.005 mg/l for the 90th percentile, and the 90th percentile copper levels were reduced to 1.04 mg/L, for the fall 1999 and Spring 2000 sampling rounds. Copper levels remain consistently below the Action Level, and IHWW has now successfully met simultaneous lead and copper control requirements of the regulations and is now in "reduced monitoring" status.