The generation and quality of streamflow on inactive uranium tailings near Elliot Lake, Ontario

Abstract

This study was undertaken to investigate the physical and chemical interactions between groundwater and surface water in an area of inactive uranium mill tailings near Elliot Lake, Ontario. The study area had a shallow water table and was drained by a single channel. Streamflow chemistry and discharge and the hydraulic response of the groundwater system were monitored for several runoff events during the period of September 1981 through May 1982. The hydrographs measured for each event were separated into groundwater and surface-water components using the mass-balance technique with Cl − and 18O as conservative tracers. The mechanisms of streamflow generation and their effect on runoff quality were evaluated on the basis of the hydrograph separations, the observed groundwater response, and the characteristics of the precipitation events. The results indicate that groundwater constitutes a significant amount of the stormflow generated in the study area. The magnitude of this contribution was dependent upon the intensity and duration of rainfall and on the initial depth to the water table. The capillary fringe played an important role in the processes of streamflow generation, both in causing a large water-table rise which increased groundwater flow to the stream, and in forming an expanding seepage face which enhanced overland flow. During runoff events the stream contained high concentrations of several dissolved inorganic species. The groundwater contribution was a major source of these constituents. The findings of this study indicate that groundwater can be a major component of streamflow during runoff events in inactive tailings areas, and as a result, can have a major influence on runoff quality. The groundwater contribution to streamflow represents an important pathway of contaminant migration to the biosphere which can be anticipated to persist for long periods of time.