AWWA WQTC62531

The District of Columbia Water and Sewer Authority (DCWASA) purchases and distributes chloraminated water to over 120,000 residences, businesses, and governmental buildings. Nitrification, the conversion of ammonia to nitrite and nitrate, is a concern for chloraminated systems. This paper describes relationships between multiple water quality parameters and nitrite formation in the WASA distribution system. In November 2000, the disinfection changed from free chlorine to chloramines. In 2003, DCWASA experienced increased lead levels due to the change in water chemistry, particularly the oxidation potential of the water. In 2004, orthophosphate was added at the treatment plants for corrosion control. Since the disinfectant change in 2000, the Aqueduct (DCWASA's wholesaler) switched disinfection from chloramines to free chlorine, or "chlorine burn," in the spring each year. Concerned for the effects on lead corrosion, the Aqueduct, DCWASA, and other purchasing utilities agreed to not perform a chlorine burn in 2005. Nitrification is a concern for chloraminated systems and without a chlorine burn, it became a primary concern for the summer months. DCWASA analyzed water quality data to identify indicators for nitrification and develop operational control levels. DCWASA was also aware of a school where nitrification occurred the previous November. DCWASA closely monitored this site and once nitrification started, researched the effects of flushing. This paper describes the data analysis conducted to identify nitrification indicators and their warning and action levels. Includes 3 references, figures.