Predicting Arsenic Intrusion in a Drinking Water Distribution System: Implications for Decontamination Strategies

摘要

Although arsenic contamination is generally considered to be an unintended consequence of groundwater disturbance, intentional or accidental introduction into drinking water is a public health concern. The toxicity of arsenic is directly related to its oxidation state; therefore, both arsenate (As(V)) and arsenite (As(III)) need to be tracked within a water distribution system in order to predict public health impacts. This paper expands upon earlier work of co-authors in which a mathematical model for the adsorption of arsenic to pipe walls in water distribution systems was developed. The arsenic model predicts arsenate, arsenite, and free chlorine concentrations in the bulk water, and adsorbed arsenic concentrations on the pipe walls. Model parameters are based on bench scale data obtained from experiments performed at EPA's Test and Evaluation Facility. The bench scale experimental results along with pilot scale experimental data from a Distribution System Simulator (DSS) pipe loop are presented. The arsenic model developed from the experimental study can be used to predict the fate and transport of contaminants within real-world water distribution systems. In addition, the arsenic model can be used to evaluate decontamination strategies (e.g., flushing and pH-modification) intended to remove arsenic from the walls of pipes or other distribution system infrastructure. Simulation studies on real-world networks are performed to compare flushing times, and locations and to investigate the benefits of different decontamination strategies in terms of the reduction of public health impacts. The EPANET-MSX software is used for the simulation study. The value of using this modeling approach in order to plan water utility decontamination activities for a wider variety of contaminants in different water distribution networks is discussed.