AWWA JAW60848

Current attempts to establish causal links between adverse health effects and the concentrations of disinfection byproducts (DBPs) in drinking water are based on infrequent measurements at the point of entry (POE) to, and a few points in, the distribution system. In this article the authors demonstrate that a chloraminated distribution system can be sampled relatively simply to obtain the median concentrations of DBPs in the tap water of a large population served by a single supply. The authors report that considerable short-term temporal variability in the DBP levels (measured in terms of trihalomethanes, haloacetic acids, and total organic halide) at the POE to a chloraminated distribution system appears to be related to the control of the addition of ammonia at the treatment plant. Samples collected every few hours over several consecutive days from the POE and from several distribution system points showed that this temporal variability at the POE most likely was dampened in the distribution system due to a combination of innate storage within the system and dynamic mixing behavior induced by variations in flow and demand. Although the variations in measured DBP concentrations in the system were relatively small and appear to be normally distributed, the variations in measured DBP concentrations at the POE were much larger. This suggests that more accurate characterization of weekly DBP concentrations throughout the chloraminated distribution system for purposes of exposure assessment can be obtained from the analysis of a single daytime-collected grab sample at a representative point in the distribution system rather than from the POE to the distribution system. Includes 25 references, tables, figures.