Speciation of /sup 99/Tc and /sup 60/Co: Correlation of laboratory and field observations

The speciation of /sup 99/Tc and /sup 60/Co in groundwater and soils contaminated with leachates from retired waste-disposal trenches is discussed. The behavior of /sup 99/Tc in soil is a complex interaction between soil-associated, reduced species of Tc and the very soluble Tc0/sub 4-bar/ anion. An association between reduced Tc species and soil organic matter is evident. Humic substances solubilized with a chelating resin contained about 8% of the soil Tc, with most of it bound in a nondialyzable form except when NaOCl was present. Added /sup 95/m/sub -/Tc0/sub 4-bar/ did not adsorb to this humic material. Density-gradient separations also confirmed the presence of a light (organic) soil fraction enriched in Tc. An anion exchange resin equilibration indicated that about 20% of the bound Tc came into solution (oxidized) at a rate of 0.015 d/sup -1/ under conditions favoring oxidation. The species of /sup 60/Co in contaminated groundwater is discussed in the context of a review of past work