Compared to Stage 1 Disinfectants and Disinfection Byproducts Rule (DBPR), what major change was made when Stage 2 DBPR was promulgated?

• A. each monitoring location has to comply with the running annual average
• B. the HAA5 maximum contaminant level was reduced to 60 mg/L
• C. to remove specific percentages of TOC based on source water alkalinity
• D. if total organic carbon substances are above 2.0 mg/L, the use of chlorine disinfectants at the beginning of the treatment process has to be reduced or eliminated

Answer: (A)

Stage 2 DBPR changed how compliance is calculated by requiring the running annual average to be met at each individual monitoring location, not just at a system-wide level. This means every site within the distribution system must show an average level of byproducts over the year that stays at or below the MCL, which helps protect people who live farther downstream or in areas with higher byproduct formation. The other options don’t reflect the actual changes introduced by Stage 2: the reported MCL values, TOC-related requirements, or chlorine-dosing rules described do not match Stage 2 changes.