Effects of rainfall events on waste-rock surface-water conditions and CO₂ effluxes across the surfaces of two waste-rock piles

The influence of rainfall events on the surface-water conditions of waste rock and the resultant CO₂ gas effluxes from waste-rock piles are of value in the development of a long-term management plan for these piles. However, data for the direct measurement of CO₂ effluxes through field-scale waste-rock piles are lacking. This study investigated the influence of a short-term, multi-day (29 July to 5 August 2002) heavy rainfall event on waste-rock water conditions and CO₂ effluxing from two large waste-rock piles at the Key Lake uranium mine in northern Saskatchewan. The study also investigated spatial and temporal variation in CO₂ effluxes in these waste-rock piles over a 2-year period (summer 2000 – summer 2002). Results showed that the impact of a heavy rainfall event on surface-water conditions and CO₂ effluxes from these waste-rock piles is of relatively short duration. Results also showed that the CO₂ effluxes were relatively uniform, both spatially and temporally (average covariance (CV) is 28%–39%), over the 2-year test period. This information can provide an important tool in the development of a long-term management plan for mine waste-rock piles. Key words: CO₂ efflux, waste-rock piles, rainfall events, unsaturated zone.