Monitoring groundwater quality and quantity is increasingly important as growing usage stresses many regional aquifers. Manual sampling provides high-quality data but is not scalable to the monitoring needs of multi-aquifer systems with large numbers of wells. This is the case in the Twin Cities Metropolitan Area of Minnesota. As a result, it is difficult to capture short-term, sub-annual variations in water quality in metropolitan areas using conventional manual sampling. Such short-term variations can help establish links between anthropogenic activities at the surface and their time-delayed expression in water quality at depth. We recommend an automated network of sensors be established in the region to monitor groundwater quality in real time. Here, we demonstrate the diagnostic ability of a pilot network of instrumented wells on the University of Minnesota campus that are within 1 km2 and screened in two different aquifers. In situ sensors have gathered more than 2 years of sub-hourly data on temperature, water elevation, and specific conductance. High-frequency measurements of these simple physical parameters from 2021 to 2023 resolved episodic fluctuations in chloride concentrations that range from less than 300 mg/L to more than 500 mg/L, the effects of transient pumping related to local construction de-watering on groundwater flow, and steadily increasing groundwater temperatures inside a major urban area ranging from 0.07 to 0.14°C/yr. This pilot demonstration of real-time groundwater monitoring is scalable in Minnesota by state agencies with statutory responsibility for groundwater quality.

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