Under the Stage 1 DBPR, how is compliance for TTHM and HAA5 determined?

Under the Stage 1 Disinfectants and Disinfection Byproducts Rule (DBPR), compliance for Total Trihalomethanes (TTHM) and Haloacetic Acids (HAA5) is determined by calculating a running annual average. This approach ensures that water systems consistently monitor and assess the levels of these disinfection byproducts over a year, rather than just a single sample point.

By averaging results over a 12-month period, it accounts for variations in disinfection byproduct levels that can occur due to seasonal changes, water source variations, and operational practices. This method promotes accountability and ensures that treatment is effective over time, protecting public health by minimizing exposure to potentially harmful contaminants present as byproducts of the disinfection process.

The running annual average method is integral in regulatory compliance because it reduces the likelihood of an isolated spike in contaminant levels being misinterpreted as compliant when the overall average might exceed allowable limits. This systematic monitoring reinforces the goal of the DBPR, which is to safeguard drinking water quality.