Like many municipalities in urban and suburban areas, San Bruno’s source water comes both from its own groundwater supply and through a purchase agreement with a major water utility — in this case, San Francisco Public Utilities Commission (SFPUC). And, like many municipalities in California, SFPUC, along with San Bruno, switched from free chlorine to chloramines in 2003 largely to reduce disinfection by-products.
At first, the conversion to chloramines didn’t present a major challenge for San Bruno, other than having to fluctuate tank water levels to maintain proper chlorine residual. However, in 2010, San Bruno and the other 26 agencies receiving SFPUC water started experiencing issues with nitrification. San Bruno first detected low chlorine residual and high free ammonia with elevated nitrite levels in two of their remote tanks. Distribution operators at San Bruno worked quickly to isolate the affected pressure zones and water tanks, flushing and draining these parts of the system in an attempt to restore acceptable water quality.