Enhancing water quality surveillance and risk assessment for shallow groundwater wells with real-time online monitoring, stable water isotopes, and microbial community data

Groundwater quality surveillance programmes and risk assessments typically rely on periodic manual sampling and laboratory analyses targeting a specific set of conventional parameters – often making them too sporadic, slow, and narrowly focused to detect water quality deficiencies in real time. To explore alternatives, we conducted enhanced monitoring of untreated groundwater quality over 12 months (February 2019–February 2020) in four shallow groundwater wells supplying potable water in Finland. We supplemented periodic manual sampling with real-time online monitoring of physicochemical and hydrological parameters, analysis of stable water isotopes from untreated groundwater and nearby surface waters, and amplicon sequencing of the 16S rRNA gene and 16S rRNA from groundwater samples. At one well, iron-related fouling of the turbidity sensor challenged implementation of real-time online monitoring, and stable water isotopes indicated problematic surface water intrusion. At two others, electrical conductivity and temperature values showed daily cyclicality, which should be considered in modelling applications. We conducted a risk assessment for each well based on all data, and developed an early warning system (EWS) by automating real-time online monitoring data collection, transfer, and analysis (using electrical conductivity and turbidity as indirect water quality indicators). Our work shows how real-time online monitoring, stable water isotope analysis and 16S rRNA amplicon sequencing can be used to enhance water quality surveillance and risk assessment for shallow groundwater wells.