Evaluating rain gardens as a method to reduce the impact of sewer overflows in sources of drinking water Laurène Autixier a,b, ⁎, Alain Mailhot c , Samuel Bolduc c , Anne-Sophie Madoux-Humery a,b,d , Martine Galarneau e , Michèle Prévost b,d , Sarah Dorner a,b a Canada Research Chair in Source Water Protection, École Polytechnique Montréal, P.O. Box. 6079, Succ. Centre-ville, Montréal, Québec H3C 3A7, Canada b Civil, Geological and Mining Engineering, École Polytechnique Montréal, C.P.6079, Station Centre-ville, Montréal, Québec H3C 3A7, Canada c INRS Centre Eau Terre Environnement, 490, rue de la Couronne Québec, Québec G1K 9A9, Canada d NSERC Industrial Chair on Drinking Water, École Polytechnique Montréal, P.O. Box. 6079, Station Centre-ville, Montréal, Québec H3C 3A7, Canada e City of Laval, Engineering Services, P.O. Box 422 Station Saint-Martin, Laval, Québec H7V 3Z4, Canada HIGHLIGHTS • A model simulating combined sewer overflow (CSO) characteristics was used. • The implementation of rain gardens was modeled and evaluated for 7 rainfall events. • Rain gardens can reduce the volume of runoff and volume of CSOs. • Reduction of CSO volumes was small for large rainfall events. • Stormwater management objectives may run counter to source water protection. abstract article info Article history: Received 4 June 2014 Received in revised form 6 August 2014 Accepted 8 August 2014 Available online 3 September 2014 Editor: D. Barcelo Keywords: Combined sewer overflows Best management practices Rain gardens Stormwater Source water protection The implications of climate change and changing precipitation patterns need to be investigated to evaluate mitigation measures for source water protection. Potential solutions need first to be evaluated under present climate conditions to determine their utility as climate change adaptation strategies. An urban drainage network receiving both stormwater and wastewater was studied to evaluate potential solutions to reduce the impact of combined sewer overflows (CSOs) in a drinking water source. A detailed hydraulic model was applied to the drainage basin to model the implementation of best management practices at a drainage basin scale. The model was calibrated and validated with field data of CSO flows for seven events from a survey conducted in 2009 and 2010. Rain gardens were evaluated for their reduction of volumes of water entering the drainage network and of CSOs. Scenarios with different levels of implementation were considered and evaluated. Of the total impervious area within the basin directly connected to the sewer system, a maximum of 21% could be alternately directed towards rain gardens. The runoff reductions for the entire catchment ranged from 12.7% to 19.4% depending on the event considered. The maximum discharged volume reduction ranged from 13% to 62% and the maximum peak flow rate reduction ranged from 7% to 56%. Of concern is that in-sewer sediment resuspension is an important process to consider with regard to the efficacy of best management practices aimed at reducing extreme loads andconcentrations. Rain gardens were less effective for large events, which are of greater importance for drinking water sources. These practices could increase peak instantaneous loads as a result of greater in-sewer resuspension during large events. Multiple interventions would be required to achieve the objectives of reducing the number, total volumes and peak contaminant loads of overflows upstream of drinking water intakes. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Combined sewer overflow (CSO) waters are a mixture of untreated sanitary waters and stormwaters (SWs) that are contaminated (Eriksson et al., 2007; Field et al., 2004; Kayhanian et al., 2003; Passerat et al., 2011; Wanielista, 1978). The problem of contamination Science of the Total Environment 499 (2014) 238–247 ⁎ Corresponding author at: Canada Research Chair in Source Water Protection, École Polytechnique Montréal, P.O. Box. 6079, Succ. Centre-ville, Montréal, Québec H3C 3A7, Canada. Tel.: +1 514 340 4711x4563. E-mail addresses: laurene.autixier@polymtl.ca (L. Autixier), alain.mailhot@ete.inrs.ca (A. Mailhot), anne-sophie.madoux-humery@polymtl.ca (A.-S. Madoux-Humery), m.galarneau@ville.laval.qc.ca (M. Galarneau), michele.prevost@polymtl.ca (M. Prévost), sarah.dorner@polymtl.ca (S. Dorner). http://dx.doi.org/10.1016/j.scitotenv.2014.08.030 0048-9697/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv