Evaluation of EPICOR-II Resin/Liner lysimeter investigation data using ``MIXBATH`` a one-dimensional transport code

The computer code MIXBATH has been applied to compare model predictions with six years of leachate collection data from five lysimeters located at Oak Ridge and five located at Argonne National Laboratories. The goal of this study was to critique the applicability of these data for use as a basis for the long-term prediction of release and transport of radionuclides contained in Portland type I-II cement and Dow vinyl ester-styrene waste forms loaded with EPICOR-II prefilter ion exchange resins. MIXBATH was useful in providing insight into information needs for long-term performance assessment. In most cases, the total activity released from the lysimeters over the test period was indistinguishable from background, indicating a need for longer-term data collection. In cases where there was both sufficient information available and activity released, MIXBATH was able to predict releases within an order of magnitude of those measured. Releases are extremely sensitive to the soil partition coefficient and waste form diffusion coefficient, and these were identified as the key data needs for long-term performance assessment.