Ra isotope activity ratio in groundwater has been recently suggested as a tool for residence time determination. 226Ra/223Ra should buildup to secular equilibrium within 5-6 half-lives of the long lived 226Ra (1000’s years). Some saline groundwater samples from a deep carbonate aquifer under the coastal plain of Israel have significantly lower than secular equilibrium ratios. This is attributed to recent (<1000 years) seawater intrusion, which further implies fast seawater circulation of up to >10m yr-1. Similar low ratios and inferred low residence times were observed in sub-permafrost groundwater in Svalbard. Notably, in both cases, some of the water showed 226Ra/223Ra significantly higher than the equilibrium ratios (226Ra/223Ra up to 150). Recent work on saline ground ice and hosting sediments in Svalbard suggests that while the short-lived 223Ra (half-life: 11.4 days) is mainly dependent on recoil and desorption from the wall-rock surface, the long-lived 226Ra also builds-up by diffusion from inside the rocks, which if time allows may result in higher than equilibrium ratios.