Data for Radium Mobility and the Age of Groundwater in Public-drinking-water Supplies from the Cambrian-Ordovician Aquifer System, North-Central USA: Table 1. Dissolved gas modeling results, environmental tracer concentrations (tritium, tritiogenic helium-3, sulfur hexafluoride, carbon-14, and radiogenic helium-4), and results for the mean age of groundwater by calibration of lumped parameter models to tracer concentrations.

High radium (Ra) concentrations in potable portions of the Cambrian-Ordovician (C-O) aquifer system were investigated using water-quality data and environmental tracers ( 3H, 3Hetrit, SF6 , 14C and 4Herad) of groundwater age from 80 public-supply wells (PSWs). Groundwater ages were estimated by calibration of tracers to lumped parameter models and ranged from modern (1 Myr) in the most downgradient, confined portions of the potable system. More than 80 and 40 percent of mean groundwater ages were older than 1000 and 50,000 yr, respectively. Anoxic, Fe-reducing conditions and increased mineralization develop with time in the aquifer system and mobilize Ra into solution resulting in the frequent occurrence of combined Ra (Rac = 226Ra [...]