Special Analysis: 2004 General Revision of Slit and Engineered Trench Limits

This Special Analysis revises the Slit Trench and Engineered Trench inventory limits. Changes have been made in the methods of analyses and in the implementation of those methods. General changes applicable to multiple pathways/scenarios are discussed in this section, while changes specific to individual pathways/scenarios are discussed in their applicable sections. This report provides limits for each nuclide for each pathway/scenario in a single table to help implement the approach introduced in the ''timed sum-of-fractions'' report. The pathways/scenarios include the following: (1) Groundwater; (2) Inadvertent Intruder; (3) Air; (4) Radon. In the timed sum-of-fractions report, the time intervals were selected to be 0-100 years, 100-1000 years, and 1000-10,000 years. The time intervals for this report were refined to 0-12 years, 12-100 years, and 100-1000 years to account for the separation of the tritium groundwater peak from those of other radionuclides. This report includes nuclides not previously included in the process analysis. Some of these nuclides are included because they have been disposed in Slit or Engineered Trenches and the latest screening analysis indicates that they survived the screening process. Other nuclides are only included because they survived the screening process and they have been disposed in other disposal units. Inventory limits for Slit Trenches and Engineered Trenches were recalculated while imposing a multitude of changes. The most important changes both tended to increase limits, such as changing the time of compliance from 10,000 years to 1000 years and tended to decrease limits, such as modifying the aquifer source node selection. The net effect for the groundwater pathway reduced some limits for nuclides that dominate the sum-of-fractions