Combining passive sampling with suspect and non-target screening (NTS) to monitor groundwater quality

The BTO project “Early Warning Systems for the quality monitoring of water resources for drinking water production” focuses on evaluating new techniques that can potentially improve current early warning systems (EWS) used to monitor the quality of ground- and surface water used for drinking water production. From this literature review, passive sampling was identified as a promising method to improve early detection of a wide range of substances in sources for drinking water, in particular groundwater (Been & Beernink, 2019). Passive sampling is per se not a monitoring technique but rather a (time-integrated) sampling approach. The latter point is what makes it particularly interesting for monitoring purposes as it allows to monitor the presence of potential contaminants in drinking water sources over longer periods of time, hence also at lower concentrations, rather than providing only a snapshot of the chemical composition, as is the case with conventional grab sampling approaches. Given the limited spatial and temporal monitoring data, passive sampling represents an interesting addition to complete our current view about occurrence of contaminants in drinking water sources.
Groundwater is the most important source for drinking water in the Netherlands and also on a global scale essential as a source for drinking water production (Giordano et al., 2009; Vewin, 2017). Groundwater quality can be affected by e.g. salinization (e.g. in coastal zones), agricultural activities and other users of the subsurface (e.g. geothermal energy) (van der Aa et al., 2014; van Loon et al., 2019). To verify suitable groundwater quality and as an early warning signal for deterioration of the groundwater quality monitoring of the groundwater is needed. Conventionally, grab samples are taken from A) monitoring wells in the proximity of the groundwater abstraction site and B) from the raw water mix that enters the treatment facility on a scheduled basis (e.g. each 2 months). Large data gaps are therefore present in the monitoring system (both in time and spatially), and it is likely that not all pollutants are being measured (Been & Beernink, 2019).

Suspect en non-target screening (NTS) is een bekende techniek om te identificeren welke stoffen (features) aanwezig zijn in watermonsters. Tijdens een pilot op pompstation Lith bleek dat er 20 keer meer stoffen in het grondwater zijn aangetroffen door NTS te combineren met passive sampling. De combinatie van passive sampling en NTS kan daarom een nuttige aanvulling vormen op de huidige grondwatermonitoringsprogramma’s van drinkwaterbedrijven. Deze combinatie van technieken maakt het namelijk mogelijk om in een vroeg stadium te identificeren welke stoffen potentieel problematisch zijn voor de toekomstige ruwwaterkwaliteit. Dit biedt meer ruimte om maatregelen tijdig in gang te zetten. De geïdentificeerde stoffen kunnen bovendien worden toegevoegd aan de reguliere monitoring middels conventionele doelstofanalyse.