RECENT ADVANCES IN DATING YOUNG GROUNDWATER - CHLOROFLUOROCARBONS, H-3 HE-3 AND KR-85/

Chlorofluorocarbons, H-3/He-3 and Kr-85 are tracers of atmospheric ori gin that can be used to date groundwater over periods from 0 to 40 yea rs. In suitable aquifers, measured groundwater ages can be used to est imate groundwater flow paths, and vertical and horizontal flow velocit ies. In simple, piston flow systems they can be used to estimate groun dwater recharge rates with an accuracy of 20% or less, better than can be achieved with traditional hydraulic-based methods. Groundwater dat ing methods have also been used to reconstruct past releases of contam inants to aquifers.