title: The effects of combined sewer overflow events on riverine sources of drinking water.
abstract: This study was set out to investigate the impacts of Combined Sewer Overflows (CSOs) on the microbiological water quality of a river used as a source of drinking water treatment plants. Escherichia coli concentrations were monitored at various stations of a river segment located in the Greater Montreal Area including two Drinking Water Intakes (DWIs) in different weather conditions (dry weather and wet weather (precipitation and snowmelt period)). Long-term monitoring data (2002-2011) at DWIs revealed good microbiological water quality with E. coli median concentrations of 20 and 30 CFU/100 mL for DWI-1 and DWI-2 respectively. However, E. coli concentration peaks reached up to 510 and 1000 CFU/100 mL for both DWIs respectively. Statistical Process Control (SPC) analysis allowed the identification of E. coli concentration peaks in almost a decade of routine monitoring data at DWIs. Almost 80% of these concentrations were linked to CSO discharges caused by precipitation exceeding 10 mm or spring snowmelt. Dry weather monitoring confirmed good microbiological water quality. Wet weather monitoring showed an increase of approximately 1.5 log of E. coli concentrations at DWIs. Cumulative impacts of CSO discharges were quantified at the river center with an increase of approximately 0.5 log of E. coli concentrations. Caffeine (CAF) was tested as a potential chemical indicator of CSO discharges in the river and CAF concentrations fell within the range of previous measurements performed for surface waters in the same area (∼20 ng/L). However, no significant differences were observed between CAF concentrations in dry and wet weather, as the dilution potential of the river was too high. CSO event based monitoring demonstrated that current bi-monthly or weekly compliance monitoring at DWIs underestimate E. coli concentrations entering DWIs and thus, should not be used to quantify the risk at DWIs. High frequency event-based monitoring is a desirable approach to establish the importance and duration of E. coli peak concentrations entering DWIs.
authors: NSERC Industrial Chair on Drinking Water, Civil, Geological and Mining Engineering, École Polytechnique de Montréal, Montréal, Québec, Canada. Electronic address: anne.madoux@polymtl.ca.
authors: Anne-Sophie
authors: AS
authors: Madoux-Humery
authors: Canada Research Chair on Source Water Protection, Civil, Geological and Mining Engineering, École Polytechnique de Montréal, Montréal, Québec, Canada.
authors: Sarah
authors: S
authors: Dorner
authors: Chemistry Department, University of Montreal, Montréal, Québec, Canada.
authors: Sébastien
authors: S
authors: Sauvé
authors: Chemistry Department, University of Montreal, Montréal, Québec, Canada.
authors: Khadija
authors: K
authors: Aboulfadl
authors: City of Laval, Engineering Services, Laval, Québec, Canada.
authors: Martine
authors: M
authors: Galarneau
authors: Écologie des Systèmes Aquatiques, Université Libre de Bruxelles, Bruxelles, Belgium.
authors: Pierre
authors: P
authors: Servais
authors: NSERC Industrial Chair on Drinking Water, Civil, Geological and Mining Engineering, École Polytechnique de Montréal, Montréal, Québec, Canada.
authors: Michèle
authors: M
authors: Prévost
mesh_terms: D002110:Caffeine / Q000032:analysis; D060766:Drinking Water / Q000382:microbiology*; D004926:Escherichia coli / Q000302:isolation & purification; D005843:Geography; D011786:Quality Control; D011792:Quebec; D011891:Rain; D045483:Rivers / Q000382:microbiology*; D012722:Sewage / Q000382:microbiology*; D012914:Snow
chemical_list: D060766:Drinking Water; D012722:Sewage; D002110:Caffeine
keywords: Caffeine; Combined sewer overflows; Drinking water intakes; Escherichia coli; Fecal indicator bacteria