Walnut Valley relies primarily on imported water from wholesalers and manages that chloraminated supply with the aid of 28 water storage tanks located throughout the service area. While monochloramine provides excellent disinfectant persistence and a decreased risk for THM production as compared to free chlorine, it naturally decomposes and generates ammonia. Ammonia becomes a food source for naturally occurring ammonia/nitrite-oxidizing bacteria (AOB/NOB) and can ultimately lead to nitrification. Aware of this risk, Walnut Valley aggressively pursued operational strategies in their water storage tanks to limit nitrification risk.
These strategies included deep tank cycling to fill tanks with “fresh” water in order to counteract water‐aging that might lead to further chloramine decomposition as well as limiting actual water storage. For example, some 30 foot tanks were routinely only filled to the 6 foot level. Additionally, as conditions worsened in the warmer summer months, operators would often valve‐off tanks and carry‐out breakpoint chlorination to impact AOB/NOB growth to prevent nitrification. As a final option, tanks could be drained and cleaned.