Flow in a brine-affected aquifer at a uranium mill tailings site near Moab, Utah, USA

Abstract

Uranium and ammonia contamination occurs in moderately saline to briny groundwater down-gradient of a 16-million-ton tailings pile on the west side of the Colorado River near Moab, Utah. Some of the water salinity was caused by historical leaching of the tailings, but the brine is mostly attributed to natural dissolution of deep evaporite sediments. It has been suggested that tailings-derived contaminants flow below the river and impact a wetlands preserve east of the river, but hydraulic data and density-dependent flow and transport modeling indicate that sub-river flow is unlikely. Moreover, water chemistry data suggest that uranium and ammonia in groundwater beneath the wetlands are naturally caused and not derived from tailings leachate.