E-Area Performance Assessment Interim Measures Assessment FY2003

Projected impacts on disposal limits of various studies have been estimated. Interim measures to compensate for the impacts are needed for the Engineered Trench and the Intermediate Level Vault. Interim measures are due to projected decreases in the radionuclide disposal limits derived from the groundwater pathway as a result of the Aquifer Source Node study and consideration of potential artificial dilution caused by the large size of the grid elements in the Intermediate Level Vault groundwater model. Recently, it became evident that, in the development of the groundwater model for the Slit Trenches, the selection of aquifer source nodes (i.e., the spatial elements of the saturated zone model into which the flux of radionuclides from the unsaturated zone model is introduced) was not optimum6. Optimizing the source nodes would likely result in increases in the resulting groundwater concentrations, which would suggest that the radionuclide disposal limits should be reduced. However, other studies may result in increases in disposal limits 7. Therefore, a decision was made to develop and implement an annual summary of the potential impact of technical studies and other information on radionuclide disposal limits and whether mitigating measures should be imposed pending completion and implementation of the studies.more » This report is the first such summary.« less