AWWA JAW61252

The proposed Stage 2 Microbial/Disinfection Byproducts Rules are intended to reduce peak concentrations of disinfection byproducts (DBPs) in distribution systems and ensure safe drinking water for all consumers. Under this rule, water utilities conducting their initial distribution system evaluations (IDSEs) must choose sampling sites that capture peak DBP concentrations. As this study shows, however, selection of monitoring locations is complicated by the fact that trihalomethane (THM) and haloacetic acid (HAA) concentrations vary over time and space in a distribution system. Data were collected from five distribution systems that had undergone DBP sampling for a variety of reasons, including research studies, operational assessments, and the monitoring required for regulatory compliance. Analysis of these data indicated that HAAs degraded in the distribution system, most frequently when chlorine or chloramine residuals were low. THM concentrations were generally high at these same sample locations. The findings presented here should provide an impetus for additional study of DBP fate and occurrence in distribution systems as well as more extensive sampling efforts. The reduction in HAA concentrations observed in this study might have gone unnoticed in the typical utility sampling program. In addition to considering more extensive sampling, water suppliers may want to implement study findings in the design of their IDSE studies or other distribution system investigations. Includes 22 references, tables.