Hydrogeologic field study of the Koongarra Uranium Deposit in the Northern Territory of Australia

Abstract

Water level, aquifer test, and slug-test data indicate that the Koongarra uranium deposit is within a low permeability, semi-confined, fractured-schist aquifer. Water levels demonstrate semi-diurnal and diurnal fluctuations related to earth tides and evapotranspiration stresses. Hydraulic test data were analyzed with homogenous isotropic and homogenous anisotropic models which allowed parameter estimation for sub-regions of the study area. Dominant anisotropy is subparallel to lithologic layering and the reverse fault. Slug tests reveal regions controlled by low storage but highly conductive fractures and isolated regions of low conductivity. Hydraulic connection of the weathered zone with the underlying schist is dependent on clay content and fractures. Environmental isotopes indicate ground water has been isolated from the atmosphere for at least 40 years and possibly several thousand years in some locations. Water budget calculations indicate the majority of recharge must be from direct infiltration through the weathered profile to account for the calculated ground-water fluxes.