Stage 2 Disinfectants and Disinfection Byproducts Rule uses sampling sites based on what evaluation approach?

• A. Worst-case sites throughout the distribution system
• B. Furthest points in the distribution system
• C. Lifetime distribution system evaluation
• D. Running annual average evaluations

Answer: (C)

Stage 2 Disinfectants and Disinfection Byproducts Rule uses sampling sites based on a lifetime distribution system evaluation. This approach looks at how the distribution system behaves over time, considering factors like water age, hydraulics, and seasonal changes, to pick representative locations where water quality reflects what customers actually receive. By using the system’s lifetime behavior, the sites chosen provide locational running annual averages that capture variability across the whole system rather than focusing on a single extreme point or simply averaging across the entire system. This makes the sampling plan more representative of typical exposure and DBP formation throughout the distribution system.