Alternative water sources can help utilities meet growing demand, comply with regulatory requirements, or provide resiliency with a more diverse source water portfolio. Before blending source waters, however, care and consideration must be given to disinfection compatibility.

Groundwater must be disinfected in accordance with the Groundwater Disinfection Rule, while surface water must be disinfected in accordance with the Stage 1 and Stage 2 Disinfection and Disinfection By-Products Rules. Most groundwater systems use free chlorine as a disinfectant, as the lack of organic matter in groundwater limits the formation of disinfection by-products. Systems that have a propensity to form chlorine-based disinfection by-products, such as many surface waters with high concentrations of organic matter, often rely on chloramines instead of free chlorine to meet drinking water standards. Issues can arise when chloramine-disinfected surface water is blended with free chlorine-disinfected groundwater.

Ammonia is added to free chlorine to form chloramines. The creation of chloramines must be carefully controlled to limit the amount of ammonia used, avoid free ammonia, and form the desired species of chloramines.

The objective is to avoid excess ammonia. Excess ammonia can become a food source for nitrifying bacteria such as Nitrosomonas, Nitrosococcus, and Nitrobacter. Once established, these bacteria can affect water quality by lowering pH and exerting a chlorine demand. Even if properly formed, as water moves through the distribution system, chloramines can degrade over time, releasing ammonia. Many states require a Nitrification Action Plan (NAP) for systems using chloramines. A NAP documents a utility’s approach to chloramination control and defines its monitoring scheme to pro-actively look for nitrification occurrences. A well-prepared NAP will include the following components:

1. Methods to control chloramination formation, with operational targets and efficiency metrics.
2. A regular system of water quality sampling and analyses to quantify concentrations of nitrate and nitrite, indicators that nitrifying bacteria are present and a threat.
3. Incremental actions to correct nitrification in a distribution system.
4. A regulatory reporting plan.
5. A public awareness plan.