Modeling Water Age and Disinfection Byproduct Formation in Drinking Water Distribution Systems in East Tennessee

Chlorine disinfection of drinking waters is responsible for the standard of health we enjoy today and the eradication of waterborne disease. Chlorine also reacts with natural organic matter (NOM) to form disinfection byproducts (DBPs) which have been linked to cancer as well as reproductive and developmental issues. The exact mechanism for formation of regulated DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs), is unknown. The literature has identified relationships between DBP formation and, most notably, characteristics of NOM, chlorine contact time, temperature, pH [negative log of hydrogen ion concentration], and chlorine dose. This study develops models both specific to individual utilities, and general to utilities with surface water sources using NaClO [sodium hypochlorite] for disinfection within the geographic region of East Tennessee. The study utilizes existing data from four utilities collected for compliance with regulations. Calibrated hydraulic models of the four distribution systems are employed to accurately determine water age (chlorine contact time) in the distribution system, often a limitation of field scale models. Multivariate power functions predict THMs and HAAs for individual utilities and across utilities with similar raw water characteristics and treatment processes. R² [coefficient of determination] ranges from 0.52 to 0.80. Developed models account for actual distribution system conditions, including water age, and predict THM and HAA levels for the four utilities with a higher R² value than applicable existing lab scale and field scale models. Results arm utilities with strategies to develop specific DBP models using existing data, control DBP levels, improve quality of drinking water, and achieve compliance with regulations.