Saltstone Disposal Facility Closure Cap Configuration and Degradation Base Case: Institutional Control to Pine Forest Scenario

Program Plan for Revision of the Z-Area Saltstone Disposal Facility Performance Assessment

“…Modeling will represent the latest closure concept (Phifer and Nelson 2003). Any changes to the closure strategy or closure system identified through the PA Revision process will be incorporated in the next revision to the closure plan.…”

Saltstone Disposal Facility Mechanically Stabilized Earth Vault Closure Cap Degradation Base Case: Institutional Control To Pine Forest Scenario

“…vaults 1 and 4) for the base case land use scenario (i.e. institutional control to pine forest scenario) and documented in Phifer and Nelson (2003). The closure cap configuration was modified from a compacted kaolin barrier layer concept to a geosynthetic clay layer (GCL) barrier layer concept.…”

“…A very small area of holes essentially controlled the hydraulic performance of the GCL. It is assumed that the infiltration remains at 14.1 inches/year until approximately year 97,000, at which point the thickness of the upper backfill above the erosion barrier is equal to the assumed evapotranspiration zone depth of 22 inches (Phifer and Nelson 2003). After year 97,000 it is assumed that infiltration through the upper GCL increases linearly from 14.1 inches/year to a maximum of 18.1 inches/year in year 280,000.…”

“…(MMES 1992;Cook et al 2000;Cook et al 2002) As part of the current SDF Performance Assessment (PA) revision, the closure cap configuration was reevaluated and closure cap degradation mechanisms and their impact upon infiltration through the closure cap was evaluated for the existing SDF concrete vaults for the base case land use scenario (i.e. institutional control to pine forest scenario) and documented in Phifer and Nelson (2003). The degradation mechanisms developed included pine forest succession, erosion, and colloidal clay migration.…”

“…These degradation mechanisms resulted in changes in the hydraulic properties of the closure cap layers and resulting increases in infiltration through the closure cap over time. Phifer and Nelson (2003) additionally recommended that the SDF closure cap barrier layer be changed from a compacted kaolin layer to a geosynthetic clay layer (GCL). It was recommended that the revised SDF closure cap consist of the following major components from the ground surface to the top of the vault roof (i.e., top to bottom), as shown in Figure 2.0-1 (Phifer and Nelson 2003):…”