Theoretical calculations together with a review of data from Sweden, Switzerland and Canada indicate that given sufficient isolation time and U and Th in the aquifer matrix, deep subsurface production of 3H, 4He, 36Cl, 39Ar, 40Ar, 85Kr, 129I, and 222Rn can overshadow the normal atmospheric component of these nuclides in recharging groundwater. Although direct evidence is lacking, calculations suggest that small but measurable subsurface production of 3H and 14C could also take place in aquifers having high U and Th concentrations. Some groundwater which has been recharged during the past 40 years will have 3H, 3He, 36Cl, 85Kr, and 129I concentrations which are dominantly anthropogenic. Dating methods with the least complications in interpretation appear to be 3H- 3He for postbomb waters and 81Kr for waters in the range of 5¿104 to 1¿106 a. ¿ American Geophysical Union 1993