On small islands such as the Magdalen Islands (Québec, Canada), freshwater is scarce—and vulnerable to saltwater intrusion. Observation wells are installed to monitor these fragile aquifers, but could they unintentionally make the problem worse?
A study published in Hydrogeology Journal https://doi.org/10.1007/s10040-026-03053-y investigates how deep, long-screen observation wells can affect nearby pumping wells in coastal aquifers. The numerical SALTFLOW model was used to test different pumping rates and distances between the pumping and observation wells. Results show that observation wells can disturb the freshwater–saltwater interface by increased mixing between fresh and saline water and creating a brackish zone of higher salinity around nearby pumping wells.
Higher pumping rates and shorter well separation distances intensified these effects, highlighting the need for careful design and placement of observation wells to protect coastal groundwater resources.
Schematic diagram of the study site on Grande Entrée Island, Magdalen Islands (Québec, Canada), showing the location of the simulated cross-section and the positions of the existing pumping well and the adjacent observation well used in the SALTFLOW model.
