title: Modelling the regional variability of the probability of high trihalomethane occurrence in municipal drinking water.
abstract: The regional variability of the probability of occurrence of high total trihalomethane (TTHM) levels was assessed using multilevel logistic regression models that incorporate environmental and infrastructure characteristics. The models were structured in a three-level hierarchical configuration: samples (first level), drinking water utilities (DWUs, second level) and natural regions, an ecological hierarchical division from the Quebec ecological framework of reference (third level). They considered six independent variables: precipitation, temperature, source type, seasons, treatment type and pH. The average probability of TTHM concentrations exceeding the targeted threshold was 18.1%. The probability was influenced by seasons, treatment type, precipitations and temperature. The variance at all levels was significant, showing that the probability of TTHM concentrations exceeding the threshold is most likely to be similar if located within the same DWU and within the same natural region. However, most of the variance initially attributed to natural regions was explained by treatment types and clarified by spatial aggregation on treatment types. Nevertheless, even after controlling for treatment type, there was still significant regional variability of the probability of TTHM concentrations exceeding the threshold. Regional variability was particularly important for DWUs using chlorination alone since they lack the appropriate treatment required to reduce the amount of natural organic matter (NOM) in source water prior to disinfection. Results presented herein could be of interest to authorities in identifying regions with specific needs regarding drinking water quality and for epidemiological studies identifying geographical variations in population exposure to disinfection by-products (DBPs).
authors.affiliation: École supérieure d'aménagement du territoire et développement regional, Université Laval, 1624 Pavillon F.A. Savard, Université Laval, Québec, Québec, Canada.
authors.forename: Geneviève
authors.initials: G
authors.lastname: Cool
authors.affiliation: École supérieure d'aménagement du territoire et développement regional, Université Laval, 1624 Pavillon F.A. Savard, Université Laval, Québec, Québec, Canada.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Lebel
authors.affiliation: School of Engineering, University of British-Columbia, Okanagan, Canada.
authors.forename: Rehan
authors.initials: R
authors.lastname: Sadiq
authors.affiliation: École supérieure d'aménagement du territoire et développement regional, Université Laval, 1624 Pavillon F.A. Savard, Université Laval, Québec, Québec, Canada. manuel.rodriguez@esad.ulaval.ca.
authors.forename: Manuel J
authors.initials: MJ
authors.lastname: Rodriguez
mesh_terms: D004203:Disinfection / Q000379:methods; D060766:Drinking Water / Q000737:chemistry*; D004784:Environmental Monitoring; D054879:Halogenation; D008962:Models, Theoretical; D011336:Probability; D011792:Quebec; D013696:Temperature; D022882:Trihalomethanes / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification / Q000379:methods; D060753:Water Quality; D014881:Water Supply
chemical_list: D060766:Drinking Water; D022882:Trihalomethanes; D014874:Water Pollutants, Chemical
keywords: Climate; Drinking water; Ecosystems; Multilevel modelling; Regional variability; Trihalomethanes