[en] Laboratory scale models have been constructed of the Pu--Am disposal areas at Los Alamos Scientific Laboratory and the migration of radionuclides determined. The laboratory model accounted for the extent and characteristics of the Pu migration quite well but did not describe as closely the features of the Am migration, probably owing to the differences in the source terms. Vertical distributions of Pu from the Chalk River Nuclear Laboratory (CRNL) disposal site have been determined on cores of the sandy clay supplied by CRNL. Iodine-129 and technetium-99, nuclides formed in the fission process, would exist as anions; I^-, IO₃^-, and TcO₄^- because of the oxidizing conditions in processing. It was found that the migration of these ions was very little retarded by rocks such as LASL tuff and Salem limestone. On the other hand, selected minerals containing copper and sulfur have been found to react strongly to remove these ions from solution and may be potential ''getter'' materials for the fixation of these ions. A study of neptunium chemistry has shown that Np(IV) and Np(V) are the most likely oxidation states of this element to exist in ground water. While Np(IV) is easily immobilized because of its extreme insolubility, Np(V) does not bind strongly to many strata. However, it has been shown in this report that minerals containing calcium carbonate or phosphate remove Np(V) from solution in ground waters. Groundwater containing Fe(II) can reduce Np(V) to Np(IV) thus converting it to a relatively immobile species. In the modeling experiments described with I^-, IO₃^-, and TcO₄^- ions as well as in the previous studies with Pu, it has been frequently observed that the distribution of the radioactive materials does not correspond to the gaussian distribution predicted by an equilibrium chromatographic calculation