Evidence for dilution of deep, confined ground water by vertical recharge of isotopically heavy Pleistocene water

New analyses of the isotopic composition of water, ¹⁴ C-dating of dissolved inorganic carbon, and order-of-magnitude Darcy calculations suggest that a dilute body of water, trending north-south in the Cambrian-Ordovician aquifer of Iowa, was emplaced as vertical recharge of Pleistocene-age water from the base of the Des Moines lobe of late Wisconsin time. The recharge occurred through more than 300 m of overlying Silurian to Mississippian age rocks. I suggest that 1) the climate at the end of the last glaciation was mild and 2) a ground-water stable isotope signature similar to that of modern precipitation in an aquifer's recharge area is not a priori evidence for relatively recent recharge. -from Author