title: Cumulative effects of fecal contamination from combined sewer overflows: Management for source water protection.
abstract: The quality of a drinking water source depends largely on upstream contaminant discharges. Sewer overflows can have a large influence on downstream drinking water intakes as they discharge untreated or partially treated wastewaters that may be contaminated with pathogens. This study focuses on the quantification of Escherichia coli discharges from combined sewer overflows (CSOs) and the dispersion and diffusion in receiving waters in order to prioritize actions for source water protection. E. coli concentrations from CSOs were estimated from monitoring data at a series of overflow structures and then applied to the 42 active overflow structures between 2009 and 2012 using a simple relationship based upon the population within the drainage network. From these estimates, a transport-dispersion model was calibrated with data from a monitoring program from both overflow structures and downstream drinking water intakes. The model was validated with 15 extreme events such as a large number of overflows (n > 8) or high concentrations at drinking water intakes. Model results demonstrated the importance of the cumulative effects of CSOs on the degradation of water quality downstream. However, permits are typically issued on a discharge point basis and do not consider cumulative effects. Source water protection plans must consider the cumulative effects of discharges and their concentrations because the simultaneous discharge of multiple overflows can lead to elevated E. coli concentrations at a drinking water intake. In addition, some CSOs have a disproportionate impact on peak concentrations at drinking water intakes. As such, it is recommended that the management of CSOs move away from frequency based permitting at the discharge point to focus on the development of comprehensive strategies to reduce cumulative and peak discharges from CSOs upstream of drinking water intakes.
authors.affiliation: Department of Civil, Geological and Mining Engineering, École Polytechnique de Montréal, 2900, boul. Édouard-Montpetit, Montréal, QC, H3T 1J4, Canada. Electronic address: isabelle.jalliffier-verne@polymtl.ca.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Jalliffier-Verne
authors.affiliation: Department of Chemical Engineering, École Polytechnique de Montréal, 2900, boul. Édouard-Montpetit, Montréal, QC, H3T 1J4, Canada. Electronic address: mourad.heniche@polymtl.ca.
authors.forename: Mourad
authors.initials: M
authors.lastname: Heniche
authors.affiliation: Department of Civil, Geological and Mining Engineering, École Polytechnique de Montréal, 2900, boul. Édouard-Montpetit, Montréal, QC, H3T 1J4, Canada. Electronic address: anne-sophie.madoux-humery@polymtl.ca.
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Madoux-Humery
authors.affiliation: Engineering Department, City of Laval, 1333, boulevard Chomedey, Rez-de-chaussée, C.P. 422 Succ. Saint-Martin, Laval, QC, H7V 3Z4, Canada. Electronic address: m.galarneau@ville.laval.qc.ca.
authors.forename: Martine
authors.initials: M
authors.lastname: Galarneau
authors.affiliation: Écologie des Systèmes Aquatiques, Université Libre de Bruxelles, Campus Plaine, CP 221, 1050, Brussels, Belgium. Electronic address: pservais@ulb.ac.be.
authors.forename: Pierre
authors.initials: P
authors.lastname: Servais
authors.affiliation: Department of Civil, Geological and Mining Engineering, École Polytechnique de Montréal, 2900, boul. Édouard-Montpetit, Montréal, QC, H3T 1J4, Canada. Electronic address: michele.prevost@polymtl.ca.
authors.forename: Michèle
authors.initials: M
authors.lastname: Prévost
authors.affiliation: Department of Civil, Geological and Mining Engineering, École Polytechnique de Montréal, 2900, boul. Édouard-Montpetit, Montréal, QC, H3T 1J4, Canada. Electronic address: sarah.dorner@polymtl.ca.
authors.forename: Sarah
authors.initials: S
authors.lastname: Dorner
mesh_terms: D060766:Drinking Water / Q000382:microbiology*; D004784:Environmental Monitoring / Q000379:methods*; D004926:Escherichia coli / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology*; D012722:Sewage / Q000382:microbiology*; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods; D060753:Water Quality
chemical_list: D060766:Drinking Water; D012722:Sewage
keywords: Combined sewer overflows; Drinking water; Escherichia coli; Hydrodynamic model; Source water protection; Urban water management