Disinfection by-products (DBPs) are known to have spatial variability in chlorinated drinking water distribution systems. This may cause difficulties in identifying sites to investigate high DBP levels for regulatory or exposure assessment purposes. Trihalomethanes (THMs) and haloacetic acids (HAAs) are the most commonly reported DBP classes and are regulated in various countries and strategies have been proposed to select the site(s) expected to have the highest formation potential for monitoring. Under the United States regulatory monitoring (Stage 2 disinfectants and DBP rule), the site selected to represent high THM levels should be, for example, either located at the extremity of the distribution system, have the longest water residence time, be located downstream a booster chlorination facility. For HAAs, the site representing high levels should also be a location with a long water residence time but where free residual chlorine is, in general, above 0.2 mg/L (especially during summer). Currently, there is no guidance on selecting locations for other DBPs. In this study, the spatial variability of non-regulated DBPs (halonitromethanes, haloacetonitriles, haloacetaldehydes, haloketones and others) in several chlorinated distribution systems of the Province of Quebec (Canada) is investigated. The data used for this study is based on research sampling programmes conducted during the past six years that considered numerous sampling locations within each distribution system (including upstream and downstream re-chlorination facilities). We will present an assessment of our analyses on how the choice of monitoring locations could influence the monitoring results for non-regulated DBPs. Then we will propose preliminary guidance on selecting sites for these new DBPs for regulatory-based surveys or exposure assessment studies.

Spatial variability of non-regulated DBPs in distribution systems: Impacts on the monitoring strategy

248th National Meeting (2014)

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