Permeability-depth relationships in crystalline rocks with applications to low-level waste repositories

Abstract

In this thesis the relationship between permeability and depth in crystalline rocks, and the estimation of inflow rates into a hypothetical underground repository for low-level radioactive waste at various depths is examined. As a result of literature review and an analysis of hydraulic conductivity as a function of depth from packer tests at Auburn dam site, mean and median hydraulic conductivity were found to decrease logarithmically with depth. The highest and lowest mean hydraulic conductivity vs. depth distributions were used in a finite difference model to compute maximum and minimum inflow rates into a repository below the water table at different depths beneath the surface. A rough approximation of the maximum inflow rate into a repository above the water table was also made using a water balance approach for various locations in the United States. The inflow rates in the unsaturated zone were one to four orders of magnitude lower than those in the saturated zone. Under saturated conditions and steady-state flow, the inflow rate decreased markedly with depth for a shallow water table and remained constant or increased slightly with depth for a deep water table.