Radionuclide Distribution Coefficients for Sediments Collected from Borehole 299-E17-21: Final Report for Subtask 1a

Over 360 distribution coefficients (KJ for cesium, iodine, selenium, Strontium, technetium, and uranium were measured in fiscal year 1998 using 20 sediments collected fkom borehole 299-El 7-21 on the Hanford Site as part of the Immobilized Low-Activity Waste-Performance Assessment (ILAW-PA). Additionally, the pH and cation-exchange capacity (a measure of the total quantity of cations that a sediment can adsorb) of these sediment samples were measured. The sediment samples originated from the Hanford formation (informal name). Statistical analyses, using Student's t-test and correlation were conducted with the measured values. There were no significant differences between layers 1 and 2 for the selenium, strontium, technetium, and uranium & values (statistics could not be applied to evaluate layer 3 v whereas the con- servative estimate was the miniium value, except for the conservative uranium&estimate that was based on the second-to-lowest value because of the presence of an unusually low value that was not consistent with other values from this borehole or previous reported values. Overall, the estimates are consistent with values used for the ILAW-PA, with some notable excep- tions. The conservative & estimates for technetium and uranium are approximately the same as those used for the ILAW-PA. The conservative ~alues for cesium, selenium, and strontium were appreciably more conservative than necessary. The conservative iodine value is appreciably less than that used in the ILAW-PA and was based on a literature review of & values measured using Hanford Site sediments. The cause for the lower iodine &values measured in borehole 299-E 17-21 sediments is not known, though the sediments used in this study clearly had appreciably lower concentrations of fme materials than the Hanford Site sediments previously used in iodine sorption measurements. These differences in &values underscore the importance of basing& estimates for the ILAW-PA on measurements using site-specific sediments.