Comparing TOTAL HAA and TOTAL THM CONCENTRATIONS using ICR data

Abstract

The US Environmental Protection Agency's Information Collection Rule (ICR) provided a rich source of occurrence data for total trihalomethanes (TTHMs) and six of the nine bromine‐ and chlorine‐containing haloacetic acids (HAAs), i.e., HAA6. A limited number of utilities participating under the ICR measured the remaining three HAAs—bromodichloroacetic acid, dibromochloroacetic acid, and tribromoacetic acid, collectively referred to as HAA3; however, extensive occurrence data for these HAA species are still lacking. An examination of the first 12 months of available ICR disinfection by‐product (DBP) data found that these three HAA species constitute a significant fraction of total HAA (HAA9) concentrations in finished drinking waters. A model was developed to estimate HAA3 occurrence using measured concentrations of trichloroacetic acid and individual TTHM species. The model estimated HAA3 concentrations reasonably well, and after estimated HAA3 concentrations were added to ICR HAA6 results, the model allowed for generation of a national distribution of total HAA occurrence. The median HAA9 level for this national distribution was approximately equal to the observed median ICR TTHM concentration. This finding suggests that THM/HAA relationships in US drinking waters need to be reevaluated with respect to DBP exposure and regulation.