Developing Novel Techniques for In Situ Nitrate Sampling, Vertical Profiling, and Real-time Remote Groundwater Quality Monitoring

English Abstract:

Certain hydrogeological settings in southern Ontario are particularly vulnerable to nitrate contamination of groundwater. Nitrate can leach into aquifers during recharge events, where it is subject to transport under spatially and temporally variable ambient flow conditions. Advancements in monitoring and data collection capabilities can improve understanding of these transport processes. Groundwater quality measurements are traditionally obtained by purging wells and analyzing samples ex situ. This “snapshot” data can disrupt the natural subsurface flow system and is not always detailed enough to determine critical water quality conditions. This research involved the application of innovative sensors to develop alternative groundwater sampling methods. Three unique methods were developed: flow cell spot sampling, depth-discrete downhole geochemical profiling and real time remote groundwater quality monitoring. While nitrate was the contaminant of focus, field parameters including temperature, DO, ORP, EC, and turbidity were also monitored. Research sites ranged from supply wells located in shallow overburden aquifers to deep fractured bedrock boreholes. Flow cell spot sampling results were compared to traditional sampling methods and were very strongly correlated (R² = 0.99). Depth-discrete profiling was used to identify groundwater quality zones corresponding to different formations. Real time remote monitoring methods were conducted by deploying sensor equipment downhole. Groundwater quality parameters were obtained every 15 minutes for several months, greatly improving the temporal resolution compared to traditional sampling. Data was transmitted in real time over the HSPA network, which allowed for remote monitoring, effectively reducing labour associated with traditional methods. The detailed datasets obtained will support future nitrate transport modelling initiatives and complement field projects in which in situ, detailed nitrate measurements are desired.