Column and batch experiments were conducted in fiscal year 1998 at Pacific Northwest National Laboratory' to evaluate the effect of varying concentrations of NaOH on the sorptive, physical, and hydraulic properties of two media: a quartz sand and a composite subsurface sediment from the 200-East Area of the Hanford Site. The NaOH solutions were used as a simplified effluent from a low-activity glass waste form. These experiments were conducted over a limited (0-to 10-month) contact time, with

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... spect to the 10,000-to 100,000-year scenarios described in the Immobilized Low-Activity Waste-Performance Assessment (ILAW-PA). Whe? these two solids were put in contact with the NaOH solutions, dissolution was evident by a substantial increase in dissolved Si concentrations in the leachates. Incremental increases in NaOH concentrations, resulted in corresponding increases in Si concentrations. A number of physical and hydraulic properties also changed as the NaOH concentrations were changed. It was observed that quartz sand was less reactive than the composite sediment. Further, moistureretention measurements were made on the quartz sand and composite sediment, which showed that the NaOH-treated solids retained more water than the non-NaOH-treated solids. Because the other chemical, physical, and hydraulic measurements did not change dramatically after the high-NaOH treatments, the greater moisture retention of the high-NaOH treatments was attributed to a "salt effect" and not to the formation of small particles during the dissolution (weathering). The distribution coefficients (Kds) for Cs and Sr were measured on the NaOH-treated sediments, with decreases from -3,000 to 1,000 and 1,300 to 300 mL/g noted, respectively, at the 0.01-to 1.0-M NaOH levels. There was no apparent trend for the Sr I<d values with contact time. The lack of such a trend suggests that dissolution of sediment particles is not controlling the drop in &; rather, it is the competition of the added Na in the various treatment solutions. It is clear from these experiments that the background chemistry of the waste-glass leachate is likely to have a significant effect on the hydrology and radionuclide geochemistry in the near-field environment of the ILAW. These experiments provided an important first approximation of several chemical and physical processes. Future research, together