PUMPING-INDUCED GROUNDWATER FLUCTUATIONS AS AN INDICATOR OF PUBLIC SUPPLY WELL VULNERABILITY

Data from several monitoring wells adjacent to public supply wells in South-Central Wisconsin show reverse water-level fluctuations (RWFs). These fluctuations are a phenomenon that occurs when water levels in wells that are open to one aquifer rise briefly in response to pumping from another aquifer. Although previous research originally reported RWFs at a single location in the area, this study added pumping and monitoring well data from five additional sites within two municipalities. This study also examined additional variables that may contribute to these water level responses and to determine how they may affect contaminant transport.

Pressure transducers in each monitoring well collected water-level data at 1-minute intervals during a 30-day period in order to monitor the response to public supply well pumping. Analysis of water-level data allowed for implementation of an automated method to isolate and characterize each RWF event in terms of magnitude and duration. Identification of RWFs in monitoring wells from multiple locations show that they are occurring over a much larger portion of the aquifer system than previously reported. Comparison between municipal supply well and monitoring well data identified correlations between well responses and pumping cycles. Additionally, the observed magnitude and duration of RWFs were related to distance between monitoring well depth and the confining layer depth. Knowledge of how these and other variables affect monitoring well responses across multiple sites may lead to a better understanding of how to mitigate public supply well vulnerability to near surface contaminants.