Optimizing short time-step monitoring and management strategies using environmental tracers at flood-affected bank filtration sites

Janie Masse-Dufresne; Paul Baudron; Florent Barbecot; Philippe Pasquier; Benoit Barbeau

doi:10.1016/j.scitotenv.2020.141429

Optimizing short time-step monitoring and management strategies using environmental tracers at flood-affected bank filtration sites

Sci Total Environ. 2021 Jan 1:750:141429. doi: 10.1016/j.scitotenv.2020.141429. Epub 2020 Aug 3.

Authors

Janie Masse-Dufresne¹, Paul Baudron², Florent Barbecot³, Philippe Pasquier⁴, Benoit Barbeau⁵

Affiliations

¹ Polytechnique Montréal, Department of Civil, Geological and Mining Engineering, C.P. 6079, succ Centre-ville, Montreal, QC H3C 3A7, Canada. Electronic address: janie.masse-dufresne@polymtl.ca.
² Polytechnique Montréal, Department of Civil, Geological and Mining Engineering, C.P. 6079, succ Centre-ville, Montreal, QC H3C 3A7, Canada. Electronic address: paul.baudron@polymtl.ca.
³ Geotop-UQAM, Chair in Urban Hydrogeology, Department of Earth and Atmospheric Sciences, C.P. 8888, succ. Centre-ville, Montreal, QC H3C 3P8, Canada. Electronic address: barbecot.florent@uqam.ca.
⁴ Polytechnique Montréal, Department of Civil, Geological and Mining Engineering, C.P. 6079, succ Centre-ville, Montreal, QC H3C 3A7, Canada. Electronic address: philippe.pasquier@polymtl.ca.
⁵ Polytechnique Montréal, Department of Civil, Geological and Mining Engineering, C.P. 6079, succ Centre-ville, Montreal, QC H3C 3A7, Canada. Electronic address: benoit.barbeau@polymtl.ca.

PMID: 32853932
DOI: 10.1016/j.scitotenv.2020.141429

Abstract

Bank filtration is a popular pre-treatment method to produce drinking water as it benefits from the natural capacity of the sediments to attenuate contaminants. Under flood conditions, bank filtration systems are known to be vulnerable to contamination, partly because flow patterns may evolve at short timescales and result in a rapid evolution of the origin and travel times of surface water in the aquifer. However, high frequency monitoring for water quality is not common practice yet, and water quality management decisions for the operation of bank filtration systems are typically based on weekly to monthly assays. The aim of this study is to illustrate how monitoring strategies of environmental tracers at flood-affected sites can be optimized and to demonstrate how tracer-based evidence can help to define adequate pumping strategies. Data acquisition spanned two intense flood events at a two-lake bank filtration site. Based on bacteriological indicators, the bank filtration system was shown to be resilient to the yearly recurring flood events but more vulnerable to contamination during the intense flood events. The origin of the bank filtrate gradually evolved from a mixture between the two lakes towards a contribution of floodwater and one lake only. Automatized measurements of temperature and electrical conductivity at observation wells allowed to detect changes in the groundwater flow patterns at a daily timescale, while the regulatory monthly monitoring for indicator bacteria did not fully capture the potential short timescale variability of the water quality. The recovery to pre-flood conditions was shown to be accelerated for the wells operating at high rates (i.e., ≥1000 m³/day), partly because of floodwater storage in the vicinity of the less active wells. These results establish new perspectives to anticipate water quality changes through selected pumping schemes, which depend on and must be adapted to site-specific water quality issues.

Keywords: Electrical conductivity; Environmental tracer; Pumping schemes; Quality precursors; Stable isotopes; Temperature.