ENGINEERED SOILS FOR LOW-LEVEL RADIOACTIVE-WASTE DISPOSAL FACILITIES - EFFECTS OF ADDITIVES ON THE ADSORPTIVE BEHAVIOR AND HYDRAULIC CONDUCTIVITY OF NATURAL SOILS

The siting of low-level radioactive waste disposal facilities requires locations having suitable soil materials beneath the proposed facilit y. These soils should be selected or designed to control water infiltr ation and ponding and enhance adsorption of radionuclides. This paper has investigated the effect of four soil additives on the hydraulic co nductivity and adsorption characteristics of two natural soils, a glac ial till and a marine clay. The additives studied in this paper were a ndisol, bentonite, clinoptilolite and hematite. The results of the hyd raulic conductivity testing indicated that remolding and recompacting the soils produced a more homogenous soil having lower hydraulic condu ctivities. Comparison of the hydraulic conductivity and adsorptive beh avior of the background soils, the additives, and mixtures of backgrou nd soils and additives indicated that andisol and clinoptilolite provi ded the most improvement with respect to increasing adsorption capacit y for iodide and strontium, respectively, with little effect on the hy draulic conductivity. The extent of adsorption and the effects of the additives on adsorption were highly pH dependent. The impact of the ad ditives was most significant at acidic pH for both strontium and iodid e adsorption because at high pH iodide adsorption was minimal for any of the materials tested and all of the background soils adsorbed a sig nificant amount of strontium at high pH. These results suggest that en gineered soils, comprised of a mixture of soil and additives, when use d below a low-level radioactive waste disposal facility can enhance th e ability of a site to retard off-site migration of radionuclides.