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

Phifer, M.A.

Savannah River Site (S.C.)

关键词: Removal;    Forests;    Storage;    Transport;    Land Use;   

DOI  :  10.2172/822342
RP-ID  :  WSRC-TR-2003-00436
RP-ID  :  AC09-96SR18500
RP-ID  :  822342

美国|英语

来源: UNT Digital Library

【 摘 要 】

The Performance Assessment (PA) for the Saltstone Disposal Facility (SDF) is currently under revision. As part of the PA revision and as documented herein, the closure cap configuration has been reevaluated and closure cap degradation mechanisms and their impact upon infiltration through the closure cap have been evaluated for the institutional control to pine forest, land use scenario. This land use scenario is considered the base case land use scenario. This scenario assumes a 100-year institutional control period following final SDF closure during which the closure cap is maintained. At the end of institutional control, it is assumed that a pine forest succeeds the cap's original bamboo cover. Infiltration through the upper hydraulic barrier layer of the closure cap as determined by this evaluation will be utilized as the infiltration input to subsequent PORFLOW vadose zone contaminant transport modeling, which will also be performed as part of the PA revision. The impacts of pine forest succession, erosion, and colloidal clay migration as degradation mechanisms on the hydraulic properties of the closure cap layers over time have been estimated and the resulting infiltration through the closure cap has been evaluated. The primary changes caused by the degradation mechanisms that result in increased infiltration are the formation of holes in the upper GCL by pine forest succession and the reduction in the saturated hydraulic conductivity of the drainage layers due to colloidal clay migration into the layers. Erosion can also result in significant increases in infiltration if it causes the removal of soil layers, which provide water storage for the promotion of evapotranspiration. For this scenario, infiltration through the upper GCL was estimated at approximately 0.29 inches/year under initial intact conditions, it increased to approximately 11.6 inches/year at year 1000 in nearly a linear fashion, and it approached an asymptote of around 14.1 inches/year at year 1800 and thereafter. At year 1800, it was estimated that holes covered approximately 0.3 percent of the GCL due to root penetration, and that this resulted in an infiltration near that of typical background infiltration (i.e. as though the GCL were not there at all). This demonstrated that a very small area of holes essentially controlled the hydraulic performance of the GCL.