RADIOISOTOPE DYNAMICS - THE ORIGIN AND FATE OF NUCLIDES IN GROUNDWATER

The use of radionuclides as clocks for groundwater dating and as probe s to investigate the geometry and spatial extent of the contact area b etween rocks and water is reviewed. Subsurface production rates for Rn -222, Ar-37, Kr-85, Ar-39, Cl-36, He-3, He-4 and Ar-40 in various rock types are listed. Measured Rn fluxes from the surface of sandstone gr ains and from pieces of granite point to scale-dependent diffusion coe fficients. The temporal evolution of subsurface-produced Rn-222-, Ar-3 7-, Kr-85- and Ar-39-activities in groundwaters yields radionuclide es cape factors between 0.1% and 9% for the Stripa granite (Sweden) and b etween 1% and 4% for the Milk River sandstone (Canada). The combinatio n of H-3, Kr-85, Ar-39, C-14, Cl-36, He-4 in the UK Triassic sandstone aquifer allows groundwater dating up to 40 000 a. Very old groundwate rs can be studied using Cl, Cl-36 and He-4 evolution as demonstrated i n the Milk River aquifer in Canada. (C) 1997 Published by Elsevier Sci ence Ltd. All rights reserved.