“…Some aquifers contained in Cretaceous-age formations in southwestern and south-central Minnesota are known to have naturally high concentrations of chloride, as much as 1,500 mg/L (Kroening and Ferrey, 2013). Upward flux of groundwater from aquifers in older formations, such as the Red River-Winnipeg aquifer contained in the Ordovician-age Red River and Winnipeg Formations in northwestern Minnesota, has been known to increase salinity in groundwater in the overlying sediments (Ruhl and Adolphson, 1986), though this type of flow system is not represented at the piezometer nests of this study.…”