Evaluation of Population-Weighted Risk Reduction for Several Disinfection By-Product Control Strategies

The purpose of this study is to develop a modeling framework to assess the impact of drinking water distribution system water-age dynamics on population-weighted disinfection by-product (DBP) risks. This approach was demonstrated by utilizing methodology from a water treatment plant model and incorporating the relative health indicator (RHI) as metric for quantifying cumulative trihalomethane and haloacetic acid risks. Distribution system network hydraulic modeling revealed that water-age dynamics can impact population-weighted DBP exposures. Using treatment modeling, it was demonstrated that DBP precursor removal at the treatment plant provides greater public health protection, as demonstrated by lower population-weighted RHI values, than granular activated carbon or aeration applied to lower DBP concentrations within the distribution system. When these population-weighted RHI reductions were normalized to the treatment process flowrates, the risk reduction of distribution system technologies tended to be equivalent to those applied at the treatment plant. It was also demonstrated that moderate population-weighted RHI reductions can be achieved for scenarios in which booster chlorination is implemented for secondary disinfection rather than as a DBP compliance strategy.