Disinfection Byproduct Occurrence at Large Water Systems After Stage 2 DBPR

Disinfection byproducts (DBPs), including total trihalomethanes (TTHM) and the sum of five haloacetic acids (HAA5) are regulated by the US Environmental Protection Agency Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR). This study compiled DBP and related water quality parameter data for 395 public drinking water systems serving populations greater than 100,000 across 44 US states from 1980 to early 2015. Assessing DBP occurrence data from two years before (2010-2012) and after (2012-2014) Stage 2 DBPR implementation shows improved capture of higher DBP exposure locations within water distribution systems due to the initial distribution system evaluation. After Stage 2 DBPR implementation, TTHM and HAA5 concentrations have mean values of 30.5 mu g/L and 19.6 mu g/L and 95th percentile values of 71.2 mu g/L and 46.5 mu g/L, respectively. Comparing this data set with the 1997-1998 Information Collection Rule data set suggests a 20 mu g/L reduction in average TTHM occurrence for the highest 5% of systems nationally from 1997-1998 to 2010-2014.