Tracer techniques in studying ground water flow and its dispersion in bedrock

Tracer techniques has been used for in-situ studies related to studies of t he final disposal of nuclear waste in Finland. Criteria for selection of th e measurement target and preliminary testing is presented. Ground water flo w rates through a packed off sections of boreholes have been measured using tracer dilution method. The results of a breakthrough test can be used to verify flow models as well as to determine parameters for the flow models. A matrix diffusion model and dispersion effected by velocity differences ar e considered. Radioactive isotopes Br-82 and Tc-99m and inactive sodium flu orescein (C20H10Na2O5) have been used as tracers.